NO342595B1

NO342595B1 - Rotary inline heave compensator

Info

Publication number: NO342595B1
Application number: NO20160909A
Authority: NO
Inventors: Tord Martinsen
Original assignee: Safelink As
Priority date: 2016-05-27
Filing date: 2016-05-27
Publication date: 2018-06-18
Also published as: NO20160909A1

Abstract

Rotary inline heave compensator (RIHC) (1) comprising minimum one drum (10), minimum one first actuator (20), consisting of a cylinder (21) and a piston (22) located inside the cylinder (21) and adapted for reciprocation with respectthereto, minimum one rack (31) and pinion (32), linking together the drum (10) and the first actuator (20) piston (22), and converts the rotational motion of the drum (10) and pinion (32) to linear motion of the rack (31) and actuator piston (22), bearing means (12) for the drum (10) to allow rotation of the drum (10), structure means (40) linking the bearing means (12) to the first actuator (20), which are immovable relative to each other, minimum one first accumulator (50) which contains a piston (52) that separates hydraulic fluid from gas, fluidly connectedthe first actuator (20) at either the rod side or the piston side of the first actuator (20), minimum one rope means (13) connected to the drum (10) in one end and a connection means (14) in the other end, adapted for securing the rope means (13) to at least one of: a vessel (3) at the sea surface and a payload (2), minimum one second connection means (14, 41) attached to either of; a rope means (13) or a fixed point on the RIHC (1), adapted for securing the rope means (13) or the RIHC (1) to at least one of: a vessel (3) at the sea surface and a payload (2).Rotary inline heave compensator (RIHC) (1) comprising at least one drum (10), minimum one first actuator (20), consisting of a cylinder (21) and a piston (22) located inside the cylinder (21) and adapted for reciprocation with respectthereto, at least one rack (31) and pinion (32), linking together the drum (10) and the first actuator (20) piston (22), and converts the rotational motion of the drum (10) and pinion (32) linear motion of the rack (31) and actuator piston (22), bearing means (12) for the drum (10) to allow rotation of the drum (10), structure means (40) linking the bearing means (12) to the first actuator (20), which is immovable relative to each other, at least one first accumulator (50) which contains a piston (52) which separates hydraulic fluid from gas, fluidly connectedthe first actuator (20) at either the rod side or the piston side of the first actuator (20), minimum one rope means (13) connected to the drum (10) in one end and a connection means (14) in the other end, adapted for securing the rope means (13) to at least one of: a vessel (3) at the sea surface and a payload (2), at least one second connection means (14, 41) attached to either of; a rope means (13) or a fixed point on the RIHC (1), adapted for securing the rope means (13) or the RIHC (1) to at least one of: a vessel (3) at the sea surface and a payload (2).

Description

ROTARY INLINE HEAVE COMPENSATOR

The rotary inline heave compensator (RIHC) is an installation tool designed to compensate vertical heave motion during sensitive installations of payloads in an offshore environment. The vertical heave source is typically generated by an installation vessel motion and/or crane tip motion and/or a secondary vessel, such as a barge, but not limited only thereto. The RIHC is designed to operate in air and in water. The RIHC is an inline tool that is based on the principles of spring isolation and may be used with active cylinder control in order to generate an efficient compensation effect.

Thus, the present invention relates to a rotary inline heave compensator provided with connection means adapted for securing the compensator to at least one of; a vessel at the sea surface and a payload.

BACKGROUND OF THE INVENTION

Many prior art passive (PHC) and active (AHC) heave compensators exist, like e.g. US 20080251980, US 20150362039, US 20080105433. The main difference between the invention and traditional PHC units is that the invention uses a drum fitted with one or more rope means as the length extension means, while a traditional PHC uses a hydraulic actuator as the length extension means. Compared to AHC, one of the differences between the prior art and the invention is for example that the RIHC is a mobile compensator for inline use with a passive backup system to go subsea with the payload being installed. Traditional active compensators often do not have a passive backup system and always stay topside on a vessel.

US 3743249 A describes an apparatus for maintaining a constant tension in a cable. The apparatus comprises a cylinder/piston assembly, a drum, spirally shaped to keep the tension in the cable independent of the position of the piston, and a rack and a pinion as a means for converting longitudinal displacements of the piston into rotation of the cable drum.

GB 2187159 A, describes a lifting apparatus with sheave blocks and compensators connected to one of the sheave blocks to prevent transmission of motions, as wave motions, from the block to carried load. A fluid actuated booster piston-cylinder assembly is interconnected with the compensator to permit greater loads to be carried for the same range of movement of the compensator.

US 2015/129529 A1 describes a marine lifting apparatus with active heave compensation including a main chassis, a drive assembly with a lifting column comprising a gear rack, a pinion, and a motor. A control circuitry is commanding the drive assembly to cause the lifting column to translate on the heave motion detected by a sensor.

The main disadvantages of the prior art are: high capital binding in permanently installed (i.e. not mobile) equipment which is often only needed a few weeks per year, high installation costs, high maintenance costs (especially related to fatigue in crane steel wire rope), poor splash zone crossing performance due to fast dynamics, poor performance for short wave periods due to fast dynamics, poor resonance protection, high power demand and lack of existing models for heavy lifts.

The invention has the following advantages compared to the prior art; lower cost for same capacity, as good performance for long wave periods and better performance for short wave periods, excellent splash zone crossing performance, well-suited for resonance protection, significantly reduced wear of the steel wire rope, low energy consumption. In addition, the use of lifting height is significantly reduced compared to cylinder based compensators, like inline PHC units. The “stroke” length can also be very long due to possible gear ratio and the possibility to rotate the drum several revolutions.

However, the compensator still uses some of the available lifting height (compared to AHC, but it uses much less than a traditional PHC), and it is required to be roughly pre-set before usage. Furthermore, when using a battery pack for the compensator, there compensation time per lift is limited by the capacity of the battery pack (this is negated if an umbilical is used).

SUMMARY OF THE INVENTION

The main features of the present invention are given in the independent claim. Additional features of the invention are given in the dependent claims.

The RIHC is basically a passive heave compensator, which traditionally is an inline tool, with an optional added active component to increase the performance. The energy source for the compensator can be either a large battery pack or an energy source on the vessel connected to the compensator via an umbilical.

According to one embodiment of the invention a RIHC comprises minimum one drum,

minimum one first actuator, consisting of a cylinder and a piston located inside the cylinder and adapted for reciprocation with respect thereto, minimum one rack and pinion, linking together the drum and the first actuator piston, and converts the rotational motion of the drum and pinion to linear motion of the rack and first actuator piston. The embodiment further comprises bearing means for the drum to allow rotation of the drum, structure means linking the bearing means to the first actuator, which are immovable relative to each other, minimum one first accumulator, fluidly connecting the first actuator at either the rod side or the piston side, minimum one rope means connected to the drum in one end and a connection means in the other end and minimum one second connection means attached to either of; a rope means or a fixed point on the compensator.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows how the drum with rope means, the rack and pinion and the actuator pistons are connected. Most other details are left out.

Figure 2 shows a more detailed version of the RIHC, with a two drum design, accumulators and tanks are not shown.

Figure 3 shows a top view of a two drum RIHC, without accumulators and tanks.

Figure 4 shows a schematic of a passive RIHC.

Figure 5 shows a schematic of an active RIHC.

Figure 6 shows a RIHC drum with variable diameter.

Figure 7 shows a placement of the RIHC in a topside lift, wherein it is located right above a payload located on a barge.

Figure 8 shows a placement of the RIHC in a subsea lift, wherein it is located right above a payload, which is symbolized with a rectangle.

Figure 9 is an illustration of a prior art compensator, permanently installed topside.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following section will describe how an active version of a rotary inline heave compensator, RIHC (1), according to the present invention works during different phases of an offshore subsea lift. It is assumed that a payload (2) is initially on a barge (4) next to an installation vessel (3), as shown in figure 7. This payload (2) has to be retrieved by the vessel (3). Then the payload (2) needs to cross the splash zone. Next there is a long descent of the payload (2) into deeper waters. And finally landing of the payload (2) on the seabed (5), as shown in figure 8. Here the payload (2) should be at rest relative to the seabed (5). An accelerometer (90) can measure the position of the compensator (1), which position is affected by the movement of the vessel (3). Drum angle sensor(s) (80) can measure the movement of the payload (2). If the payload (2) is not at rest, the means for hydraulic fluid transportation (180), which is a pump, will either push or brake the piston (152) in the second actuator (150), so that the net movement of the payload (2) will be zero. Communication means (110) transfers signals from the vessel about crane winch spooling to the compensator (1), so that such effects can be quickly incorporated into the actions of the means for hydraulic fluid transportation (180).

The RIHC (1) can comprise a sensing arrangement or means, such as for example at least one drum angle sensor (80), shown with alternative placements in figure 5, e.g. on the drum (10), in the first actuator (20), in the second actuator (150), in the first accumulator (50) or in the pressure intensifier (170). Based on direct or indirect measurements from at least one of these sensors (80), along with measurements from an accelerometer (90) and/or a water pressure sensor (100) and/or communication means (110), the RIHC (1) will be able to calculate how a means for hydraulic fluid transportation (180) should operate to transport hydraulic fluid between a hydraulic fluid volume in the pressure intensifier (170) and another hydraulic fluid volume in the second accumulator (130) in order to continuously have a net zero relative motion between at least one of the connection means (14) and the seabed (5).

When the payload (2) at the barge (4) is connected to the RIHC (1), the torque acting on the drum (10) is increased to almost carry the load (about 90 % of static weight) of the payload (2). When desired by the crane operator, a fast pressure increase can be performed to quickly lift (i.e. faster than normal crane speed) the payload (2) from the barge (4) in order to reduce risk of contact between the barge (4) deck and the payload (2) after lift-off, the pressure increase is performed by injecting gas from a second tank (70) or by using the means for hydraulic fluid transportation (180). The barge (4) is then relocated, and the payload (2) is ready to cross the splash zone. During the splash zone crossing phase, the RIHC (1) is operating in a passive mode, with no active control of the drum (10), except for equilibrium adjustments (wanted equilibrium angle (or “stroke”) is pre-set) due to environmental disturbances, such as increased buoyancy and/or changing temperature. After crossing the splash zone, the stiffness of the RIHC (1) is reduced by connecting a first tank (60). This is crucial to provide good resonance protection. During the lowering phase, the pump (180) can be used to charge an energy source (144), adapted for supplying the RIHC (1) with power, by utilizing the hydraulic fluid flow in the RIHC (1). The equilibrium angle (or “stroke”) of the drum (10) is maintained by a means for gas transportation (140) that adjusts the pressure of the different gas volumes in the RIHC (1). The landing phase mode is either activated based upon water depth or activated by an ROV (the ROV turns a switch on the RIHC (1)). During this phase, the heave motion of the payload (2) will be close to zero, and it can safely be installed. The heave motion is partly compensated by the passive spring (i.e. a gas volume in the first accumulator (50), and a gas volume in the first tank (60)), and partly by the means for hydraulic fluid transportation (180), transferring fluid in and out of the second actuator (150) via the pressure intensifier (170).

The sketches or figures shown are intended to show the principles of the invention, wherein numerous variations with a number of accumulators and tanks can be utilized in order to get the same results. The component description is identified in Table 1.

Figure 1 illustrates how the drum (10) rotation is transferred into linear motion via a rack (31) and pinion (32). The rack (31) is connected to pistons (22, 152) at each end. The two rope means (13) shown are connected to the crane hook and to the payload (2) respectively. The weight of the payload (2) generates torque on the drum (10) which is transferred as a linear force to the rack (31) via the pinion (32). “Stroke” is increasing when the drum (10) is rotating counter clockwise and reducing when it is rotating clockwise. The actuators (20, 150) can be with or without stuffing box, in any case they compensate water pressure as they have an equal area on either rod (rack (31)) or piston (22, 152) or both. Pressure from a passive and active system is applied to the actuators (20, 150) to counteract the force from the drum (10) torque.

Figure 2 illustrates a two drum (10) version of the RIHC (1), seen from the side, while figure 3 shows a two drum (10) version seen from the top. Accumulators, tanks and other parts are not shown. The two drum version makes it easy to get the centre of gravity in the middle of the compensator (1) and it will not change with drum (10) angle. Two actuators (20, 150) are used per drum (10), however it seems feasible to use just two actuators (20, 150) in total if an extra pinion (32) is used to get the correct rotational direction (i.e. the drums should rotate opposite of each other). The rope means (13) from the drums (10) are connected together using construction means (15) and have connection means (14) fitted so that i.e. shackles can be connected. Construction means (40) forms a stiff connection between the actuators (20, 150) and the bearing means (12) used to support the drum (10) axles (11). If long “stroke” is not needed, then it’s possible to connect either the crane hook or payload (2) to the alternative connection means (41).

Figure 4 shows a schematic for a passive RIHC (1). For simplicity only one drum (10) is shown, but more than one may be used. Clockwise rotation of the drum (10) causes one or more rope means (13) to be spooled off the drum (10) when force is applied to the connection means (14). A pinion (32) is connected to the drum (10) and converts rotational motion of the drum (10) to linear motion of the rack (31). The rack (31) in turn is connected to two pistons (22, 152) located inside two actuators (20, 150). Piston side on one actuator should be connected to rod side on the other actuator. This can be done in two ways, the way shown in figure 4 is suitable for clockwise rotation of the drum (10) (to increase torque), while the opposite way is suitable for counter clockwise rotation of the drum (10) (to increase torque). A conduit means connects the two actuators (150, 20) to the first accumulator (50) via a valve means (160). The valve means (160) is used to block or partially block the flow of hydraulic fluid from the actuators (20, 150) to the first accumulator (50). The first accumulator (50) contains a piston (52) which separates hydraulic fluid from gas. Conduit means further connects the gas side of the first accumulator (50) to a first tank (60) via valve means (161, 162), which may be independently closed, partially closed or fully open. The first tank (60) can be used as a gas storage vessel or to increase the gas volume of the first accumulator (50). A second tank (70) is used to store high pressure gas.

A means for gas transportation (140), consisting of a pressure intensifier (141), connected to a pump (142), connected to a motor (143), connected to an energy source (144), is used to transport gas between the first accumulator (50), the first tank (60), the second tank (70) and the surroundings. The means for gas transportation (140) enables transport of gas even when there is a negative differential pressure. Valve means (165, 164, 163) are used to control gas flow in and out of the means for gas transportation (140). Drum angle sensor(s) (80), which may be located in one or both of the actuators (20, 150), the first accumulator (50) or on the drum (10) is used to measure the “stroke” of the compensator (1) as a function of the angle of the drum (10).

Figure 5 shows a schematic for an active RIHC (1). For simplicity only one drum (10) is shown, but more than one may be used. Clockwise rotation of the drum (10) causes one or more rope means (13) to be spooled off the drum (10) when force is applied to the connection means (14). A pinion (32) is connected to the drum (10) and converts rotational motion of the drum (10) to linear motion of the rack (31). The rack (31) in turn is connected to two pistons (22, 152) located inside two actuators (20, 150). The piston side of one actuator is connected to the first accumulator (50) via a valve means (160). The valve means (160) is used to block or partially block the flow of hydraulic fluid from the actuators (20, 150) to the first accumulator (50). The first accumulator (50) contains a piston (52) which separates hydraulic fluid from gas. Conduit means further connects the gas side of the first accumulator (50) to a first tank (60) via valve means (161, 162), which may be independently closed, partially closed or fully open. The first tank (60) can be used as a gas storage vessel or to increase the gas volume of the first accumulator (50). A second tank (70) is used to store high pressure gas. The rod or piston side or both of the other actuator (in this example 150) is connected to a pressure intensifier (170) via conduit means. The pressure intensifier consists of two cylinder (173, 174), a piston (172) and a rod (171). It is used to increase the flow rate of the means for hydraulic fluid transportation (180) by a ratio equal to the area ratio of the piston (172) and rod (171). The means for hydraulic fluid transportation (180) is connected to a second accumulator (130), which contains both oil and gas separated by a piston (132), via conduit means. The means for hydraulic fluid transportation (180) is powered by a motor (181) that gets energy from an energy source (144), which may be a battery pack or an energy source located on the vessel (3). The means for hydraulic fluid transportation (180) is controlled based on measurements from the drum angle sensor (80), the accelerometer (90) and/or the water pressure sensor (100) and/or the communication means (110). The communication means (110) transfers information about crane motion and/or crane winch spooling to the compensator (1).

Figure 6 shows a drum (10) with variable diameter versus rotational angle. The variable diameter can reduce the need for gas volume significantly as almost constant torque can be achieved by varying the moment arm in the same way as the gas pressure varies during compression. The result is close to constant torque versus rotational angle, which significantly increases the performance of the passive system and reduces the energy need for the active system.

Figure 7 shows the RIHC (1) while being used to lift a payload (2) from a barge (4). A first MRU (6), short for motion reference unit, is placed in the crane tip. The first MRU (6) can transfer its measurements to the RIHC (1) either via umbilical or via wireless signals (e.g. when topside). A second MRU (7) can be placed close to the payload (2), or other payloads, to be lifted off a floating object topside, such as e.g. a barge (4). The second MRU (7) can transfer its measurements to the RIHC (1) via e.g. wireless signals. The two MRU units (6, 7) allow the RIHC (1) to accurately compensate for heave motions of two vessels (i.e. the barge (4) and the vessel (3) when the RIHC (1) is topside). Crane hoisting speed is not disturbed as it can be effectively calculated based on the available measurements. As mentioned the MRUs (6, 7) can transfer the measurements to the RIHC (1) wirelessly or via an umbilical, but not limited only thereto.

At least one of the cylinders can be constituted or presented as a group of a predetermined number of cylinders. The predetermined number of cylinders can be arranged in a parallel connection in order to increase the effective volume of at least one volume of the gas and/or hydraulic fluid volumes.

Figure 8 shows the RIHC (1) while being used to lower a payload (2) from a vessel (3) to the seabed (5).

Table 1

Claims

1. Rotary inline heave compensator (1) provided with connection means (14,41) adapted for securing the compensator (1) to at least one of; a vessel (3) at the sea surface and a payload (2)

characterized in that the compensator (1) comprises

minimum one drum (10);

minimum one actuator (20), consisting of a cylinder (21) and a piston (22) located inside the cylinder (21) and adapted for reciprocation with respect thereto;

minimum one rack (31) and pinion (32), linking together the drum (10) and the actuator (20) piston (22), and converts the rotational motion of the drum (10) and pinion (32) to linear motion of the rack (31) and actuator piston (22);

bearing means (12) for the drum (10) to allow rotation of the drum (10);

structure means (40) linking the bearing means (12) to the cylinder (21) of the actuator (20), which are immovable relative to each other;

minimum one accumulator (50) which contains a piston (52) that separates hydraulic fluid from gas, fluidly connected to the actuator (20) at either the rod side or the piston side of the actuator (20);

minimum one rope means (13) connected to the drum (10) in one end and the connection means (14) in the other end, adapted for securing the rope means (13) to at least one of: the vessel (3) at the sea surface and the payload (2);

minimum one second connection means (14, 41) attached to either of; the rope means (13) or a fixed point on the RIHC (1), adapted for securing the rope means (13) or the RIHC (1) to at least one of: the vessel (3) at the sea surface and the payload (2).

2. Rotary inline heave compensator (1) according to claim 1, further comprising:

valve means (160), used to block or partially block the flow of hydraulic fluid from the actuator (20) to the accumulator (50);

conduit means connecting the gas side of the accumulator (50) to a tank (60) via valve means (161, 162), which may be independently closed, partially closed or fully open;

the minimum one tank (60) that can be used as a gas storage vessel or to increase the gas volume of the accumulator (50);

a minimum one second tank (70) for high pressure gas;

a means for gas transportation (140), consisting of a pressure intensifier (141), connected to a pump (142), connected to a motor (143), connected to an energy source (144), to transport gas between the first accumulator (50), the tank (60), the second tank (70) and the surroundings;

drum angle sensors (80).

3. Rotary inline heave compensator (1) according to claim 2, where the drum angle sensor (80) is located in one or both of the actuator (20) and a minimum one second actuator (150), the accumulator (50) or on the drum (10).

4. Rotary inline heave compensator (1) according to one of the claims 1-3 , comprising: a minimum one second actuator (150), consisting of a cylinder (151) and a piston (152), where the piston (152) is connected to the rack (31), and adapted for reciprocation with respect thereto.

5. Rotary inline heave compensator (1) according to one or more of claims 1-4, comprising two actuators (20,150) where a second actuator (150) comprises a cylinder (151) and a piston (152), where the piston (152) is connected to the rack (31), and adapted for reciprocation with respect thereto and

conduit means connecting the second actuator (150) to the actuator (20).

6. Rotary inline heave compensator (1) according to one or more of claims 1-5, further comprising:

minimum one accelerometer (90).

7. Rotary inline heave compensator (1) according to one or more of claim 1-6, further comprising:

minimum one pressure sensor for seawater pressure (100).

8. Rotary inline heave compensator (1) according to one or more of claims 2-7, further comprising:

a second accumulator (130), consisting of a cylinder (131) and piston (132), connected to a means for gas transportation (140) via conduit means.

9. Rotary inline heave compensator (1) according to one or more of claims 2-8, further comprising:

valve means (165, 164, 163, 166) to control gas flow in and out of a means for gas transportation (140).

10. Rotary inline heave compensator (1) according to one or more of claims 1-9, further comprising:

communication means (110) transferring information from the vessel (3) to the compensator (1).

Rotary inline heave compensator (1) according to one or more of claims 7-10, further comprising:

a minimum one pressure intensifier (170) connected to a second actuator (150) via conduit means and to a second accumulator (130) via conduit means, consisting of two cylinders (173, 174), a piston (172) and a rod (171);

minimum one pump (180), connected to the pressure intensifier (170) and the second accumulator (130) via conduit means.

Rotary inline heave compensator (1) according to one or more of claim 1-11, wherein the drum (10) has a variable diameter with angle.