NO342866B1

NO342866B1 - Active heave compensator

Info

Publication number: NO342866B1
Application number: NO20161247A
Authority: NO
Inventors: Tord Martinsen; Andre Skare Berg
Original assignee: Safelink As
Priority date: 2016-07-29
Filing date: 2016-07-29
Publication date: 2018-08-20
Also published as: NO20161247A1

Abstract

Active heave compensator (100) comprising a hydraulic actuator (10), comprising of a first cylinder (1) having an upper end and a lower end, a first piston rod (13) connected to a first piston (12) and extending downwardly therefrom through the lower end of the first cylinder (11), adapted for reciprocation with respectthereto, connection means (14) mounted at the upper and lower end of the hydraulic actuator (10) adapted for connecting the active heave compensator (100) to a floating object, like a vessel (102) mounted crane, and a payload (101), a first volume (V1), filled With hydraulic fluid, located between the first piston (12) and the lower end of the first cylinder (11), a second volume (V2), filled with gas at any pressure including zero, located between the first piston (12) and the upper end of the first cylinder (11), a double acting gas accumulator (30), comprising of a fourth cylinder (31), a ring shaped piston (32) mounted concentrically within the fourth cylinder (31) and adapted for reciprocation with respectthereto, where the lower end of the ring shaped piston (32) is on the same side as the lower end of the fourth cylinder (31) when ring shaped piston (32) is at zero stroke, a third inner cylinder (33) mounted concentrically within the fourth cylinder (31) and fixed to the upper end of the fourth cylinder (31) with a leak tight connection, a fourth inner cylinder (35) mounted concentrically inside the fourth cylinder (31) and connected to the upper end of the ring shaped piston (32) with a leak tight connection, a cylinder end (34) mounted concentrically with the fourth cylinder (31) at the upper end of the fourth inner cylinder (35) with a leak tight connection, a Fifth inner cylinder (36) mounted concentrically with the fourth cylinder (31) at the lower end of the fourth cylinder (31) in a leak tight manner, where the assemblyconsisting of the ring shaped piston (32), the fourth inner cylinder (35) and the cylinder end (34) is adapted to reciprocate inside the fourth cylinder (31), inside the third inner cylinder (33) and outside the fifth inner cylinder (36) in a leak tight manner, a sixth volume (V6), filled with hydraulic fluid, located between the cylinder end (34), the inside of the fourth inner cylinder (35), the fifth inner cylinder (36) and the lower end of the first cylinder (31), a seventh volume (V7), filled with hydraulic fluid, located between cylinder end (34), the outside of the fourth inner cylinder (35), the inside of the third inner cylinder (33) and the upper end of the firstActive heave compensator (100) comprising a hydraulic actuator (10) comprising a first cylinder (1) having an upper end and a lower end, a first piston rod (13) connected to a first piston (12) and extending downwardly therefrom through the lower end of the first cylinder (11), adapted for reciprocation with respectthereto, connection means (14) mounted on the upper and lower end of the hydraulic actuator (10) adapted for connecting the active heave compensator (100) to a floating object, like a vessel (102) mounted crane, and a payload (101), a first volume (V1) filled with hydraulic fluid located between the first piston (12) and the lower end of the first cylinder (11), a second volume (V2) filled with gas at any pressure including zero located between the first piston (12) and the upper end of the first cylinder (11), a double acting gas accumulator (30) comprising a fourth cylinder (31), a ring shaped piston (32) mounted concentrically within the fourth cylinder (31) a nd adapted for reciprocation with respectthereto, where the lower end of the ring shaped piston (32) is on the same side as the lower end of the fourth cylinder (31) when ring shaped piston (32) is at zero stroke, a third inner cylinder (33) mounted concentrically within the fourth cylinder (31) and fixed to the upper end of the fourth cylinder (31) with a leak tight connection, a fourth inner cylinder (35) mounted concentrically inside the fourth cylinder (31) and connected to the upper end of the ring shaped piston (32) with a leak tight connection, a cylinder end (34) mounted concentrically with the fourth cylinder (31) at the upper end of the fourth inner cylinder (35) with a leak tight connection , a Fifth inner cylinder (36) mounted concentrically with the fourth cylinder (31) at the lower end of the fourth cylinder (31) in a leak tight minor, where the assembly consistency of the ring shaped piston (32), the fourth inner cylinder (35) and the cylinder end (34) is adapted to recipr ocate inside the fourth cylinder (31), inside the third inner cylinder (33) and outside the fifth inner cylinder (36) in a leak tight less, a sixth volume (V6) filled with hydraulic fluid located between the cylinder end ( 34), the inside of the fourth inner cylinder (35), the fifth inner cylinder (36) and the lower end of the first cylinder (31), a seventh volume (V7), filled with hydraulic fluid, located between cylinder end ( 34), the outside of the fourth inner cylinder (35), the inside of the third inner cylinder (33) and the upper end of the first

Description

The active heave compensator (AHC) is an installation tool designed to compensate heave motion during sensitive lifts in an offshore environment. The heave is typically induced by swells that causes floating objects, like installation vessels and barges, to move vertically up and down. The AHC is designed to operate in air or in water. The AHC is an inline tool that combines the principles of spring isolation with active cylinder control in order to generate an efficient compensation effect. The tool can operate like a traditional gas-over-hydraulic fluid spring-dampening device if the active component fails. During offshore construction high and heavy structures are to be lowered by expensive working ships with big cranes of high carrying capacity. The structures have to be lifted from fixed or floating objects and be placed on either fixed or floating locations, topside or subsea. Irregular movements of working ships, barges and supply vessels generated by swell and wind can be increased a lot by the crane boom, so that even with average swell it is difficult or impossible to carry by the crane sensitive structures during violent ship and crane movements and to lower them subsea. Since daily costs of operation with working ships are very high, each delay causes enormous additional costs. Therefore, a strong demand exists to perform respective works also in less favourable weather and with average swell without damaging the structures to be moved. The prior art compensation devices, such as crane mounted active heave compensators, have a very high capital cost and have several weaknesses, where the biggest ones are; poor mobility, poor splash zone crossing performance, fatigue problems with wire rope, many lack passive backup systems, high power demand and lack of models for heavy lifts.

EP 2982638 A1 describes a heave compensator where pressure in liquid filled chamber beneath the load bearing first piston is controlled by transportation of liquid from another chamber with liquid filled chamber beneath a second piston and gas above piston, transportation of liquid is controlled by a sensing arrangement measuring equilibrium position of first piston and controlling a valve between the two fluid filled chambers.

US 5209302 A describes a compensation system for marine vessels with heave and compensating sensors, a microprocessor and a responsive operator to act upon the compensation elements of the system.

NO 20140672 A describes a self-adjusting heave compensator with an actuator with vacuum above load bearing first piston and oil filled chamber beneath load bearing first piston fluidly connected with a first gas over fluid accumulator which is further fluidly connected with gas chamber of second gas over fluid accumulator. First accumulator is also fluidly connected with respectively low and high pressure gas chambers controlled by valves. Actuator piston is controlled by a position sensor, measuring equilibrium position to the piston and thereby regulate in order to increase or decrease pressure in system,

US 3946559 A describes a heave compensating device with a passive load-supporting system comprising a heave compensating cylinder with a piston and a piston rod connected to a load, the top of the cylinder is connected to a fixed support, i.e. on a floating platform. Cylinder is in lower chamber fluidly connected to a dashpot cylinder with a piston. The other end of the dashpot cylinder is connected to an air cylinder constituting a closed air system. A pressure sensor device is in operative connection with both ends of the dashpot cylinder and controls a pump which has a piston connection to the dashpot cylinder.

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 AHC consists of a hydraulic actuator connected to one or more advanced gas accumulators, which further is connected to one or more gas tanks. The advanced gas accumulator allows for very efficient use of commercially available hydraulic pumps that are used to gain actively control the hydraulic actuator. Further, the AHC has two different ways to compensate for external water pressure, a compact and efficient passive system and an active system. Other influences like temperature variations and load variations are also handled by the active compensation system, which is able to increase or reduce gas pressure in tanks and accumulators individually by use of control valves and gas boosters. Automatic control of the hydraulic actuator is used to compensate for heave motion. The automatic control is controlled by a computer that calculates the control signal based on measurements from several sensors, where the most important ones are the piston position sensor, the accelerometer and the wire rope speed sensor. Information about the wire rope speed is transferred to the compensator with wireless signals while the compensator is in air and with acoustic transmission while it is submerged. The compensator can operate in several different modes with variable stiffness and damping with or without active control of the hydraulic actuator and with or without active control of the pressure levels in the various gas volumes. The compensator is energy efficient due to the fact that passive part of the compensator carries the entire load of the payload weight and the actively controlled hydraulic pumps only have to compensate for gas compression effects and friction, which typically is about 15 % of the force compared to static force. Energy regeneration is also used so that only friction and oil leakage and mechanical losses in the hydraulic pump contributes to the energy consumption. For AHC units with active depth compensation the power consumption is further lowered due to reduced friction at deep waters. Further, acoustic communication subsea and wireless communication topside allows for control and monitoring of the compensator, on-board sensors allows the user to verify performance after a lift is concluded.

The invention has the following advantages compared to the prior art; mobile construction, 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, reduced wear of the steel wire rope, low energy consumption.

The main features of this patent application, which is not covered in detail by previous applications:

- The use of a double acting gas accumulator, which utilizes normal hydraulic pumps at a much higher level than prior art (as the pump can apply full pressure in two directions at relatively low flow rates) and removes the need for large dedicated accumulators

- The depth compensator, which is much more compact and light than prior art (can typically use one small depth compensator, compared to usually two large ones for prior art)

- Use of acoustic communication with the vessel to reduce lag in crane operator commands.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an embodiment of the AHC with passive depth compensation.

Figure 2 shows an embodiment of the AHC with active depth compensation.

Figure 3 shows a placement of the AHC in a subsea lift, wherein it is located right above a payload, which is symbolized with a rectangle.

Figure 4 shows a placement of the AHC in a topside lift, wherein it is located right above a payload located on a barge.

Figure 5 is an illustration of a prior art active heave compensator, permanently installed topside.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following section will describe how an active heave compensator (100) or AHC for short, according to the present invention works during different phases of an offshore subsea lift. It is assumed that a payload (101) is initially on a barge (103) next to an installation vessel (102), as shown in figure 4. This payload (101) has to be retrieved by the vessel (102). Then the payload (101) needs to cross the splash zone. Next there is a long descent of the payload (101) into deeper waters, and finally landing of the equipment (101) on a seabed (106), as shown in figure 3.

There are different requirements to functionality during the different phases of the lifting operation. During the first phase, which is lifting of a payload (101) that is located a floating barge (103) from a floating vessel (101), it is beneficial if the active heave compensator (100) can compensate motion in such a way that the relative motion between the lower part of the compensator (100) and the barge (103) deck is zero. This functionality requires that three things are known:

1. Velocity of the barge deck

2. Velocity of the crane hook

3. Winch speed (i.e. wire rope spooling velocity)

The first requirement is handled by a wireless MRU (104) placed on the barge (103) deck, preferably close to the payload (101). The second requirement is either handled by an accelerometer inside the active heave compensator (100), or by a MRU (105) located on the vessel (102) or in the crane. The final requirement is normally given by the crane computer, and is transferred wirelessly to the active heave compensator (100).

Based on the information above the computer inside the active heave compensator (100) is able to control the hydraulic actuator (10) in such a way that the relative motion between the lower part of the active heave compensator (100) and the barge (103) deck is close to zero while the crane winch is not spooling out wire rope. During spooling the computer inside the active heave compensator (100) will take this into account to not cause any lag for the crane operator.

After successful connection and lifting of the payload (101) from the barge (103) deck, the payload (101) has to cross the splash zone (i.e. the border between air and sea), where different requirements apply. This phase is characterized by fast dynamics, where unpredictable forces from slamming and buoyancy occurs and is best suited for a passive heave compensator, which the active heave compensator (100) basically is. Active hydraulic actuator (10) control is turned off, stiffness and damping is adjusted to the best possible settings by use of control valves (CV). During the actual crossing of the splash zone the hydraulic actuator (10) piston rod (13) tends to move towards the inner position due to buoyancy forces acting on the payload (101). This effect is compensated by adjusting the internal gas pressure in one of the following ways:

1. Release gas to the surroundings

2. Transfer gas from the double acting gas accumulator (30) to a tank with lower pressure 3. Transfer gas from the double acting gas accumulator (30) to a tank with higher pressure by utilizing the gas booster (70)

The adjustment is performed automatically by the on-board computer based on changing piston rod (13) equilibrium position.

A certain distance after crossing the splash zone, the active heave compensator (100) will often switch to a softer setting with less damping. This is done to prevent resonance in the lifting arrangement. If the passive system alone is not enough, then the piston rod (13) can either be locked by closing control valves or actively controlled by the computer to prevent resonance.

During the transport from shallow waters to deeper waters two effects influence the equilibrium position of the piston rod (13). The first influence is that the water temperature often tends to decrease as the active heave compensator (100) is lowered into deeper waters. This affects the piston rod (13) equilibrium due to the fact that the gas pressure in all gas volumes are reduced due to lowered temperature. The active heave compensator (100) compensates this either by transferring gas under higher pressure from one of the tanks to the double acting gas accumulator (30) via control valves or from a tank under lower pressure to the double acting gas accumulator (30) via the booster (70) and control valves. The second and often most important effect is the increasing water pressure. The active heave compensator (100) comes in two versions that handles this issue in different ways:

1. The active heave compensator (100) shown in figure 1 has a passive depth compensator (20) that via suitable area ratios effectively cancels the water pressure effect by pressurizing the inside of the piston rod (13).

2. The active heave compensator (100) shown in figure 2 has an active depth compensation system that adjusts gas pressure on both sides of the first piston (12) so that the water pressure effect is cancelled. The system is controlled by the on-board computer and can in many cases provide better performance than the passive system shown in figure 1, however the passive system is more robust.

During the final phase of the lifting operation, which is the landing phase, the active hydraulic actuator (10) control is again activated, either by acoustic commands, water pressure triggering or by an ROV, to ensure that there is minimal relative velocity between the lower end of the active heave compensator (100) and the seabed (106). The on-board computer uses the on-board accelerometer, the piston rod (13) position sensor as well as acoustically transmitted signals from the vessel about wire rope spooling to control the hydraulic actuator (10) to a high degree of accuracy and without crane operator lag.

Figure 1 illustrates a passive depth compensated embodiment of an active heave compensator (100) with all major sub-components numbered. Figure 2 illustrates an active depth compensated embodiment of an active heave compensator (100) with all major sub-components numbered.

The next section describes the common elements between the two figures, while the next two describes the particular elements of figure 1 and figure 2.

The active heave compensator (100) comprises:

- a hydraulic actuator (10), comprising of a first cylinder (11) having an upper end and a lower end, a first piston rod (13) connected to a first piston (12) and extending downwardly therefrom through the lower end of the first cylinder (11), adapted for reciprocation with respect thereto, connection means (14) mounted at the upper and lower end of the hydraulic actuator (10) adapted for connecting the active heave compensator (100) to a floating object, like a vessel (102) mounted crane, and a payload (101)

- a first volume (V1), filled with hydraulic fluid, located between the first piston (12) and the lower end of the first cylinder (11)

- a second volume (V2), filled with gas at any pressure including zero, located between the first piston (12) and the upper end of the first cylinder (11)

- a double acting gas accumulator (30), comprising of a fourth cylinder (31), a ring shaped piston (32) mounted concentrically within the fourth cylinder (31) and adapted for reciprocation with respect thereto, where the lower end of the ring shaped piston (32) is on the same side as the lower end of the fourth cylinder (31) when ring shaped piston (32) is at zero stroke, a third inner cylinder (33) mounted concentrically within the fourth cylinder (31) and fixed to the upper end of the fourth cylinder (31) with a leak tight connection, a fourth inner cylinder (35) mounted concentrically inside the fourth cylinder (31) and connected to the upper end of the ring shaped piston (32) with a leak tight connection, a cylinder end (34) mounted concentrically with the fourth cylinder (31) at the upper end of the fourth inner cylinder (35) with a leak tight connection, a fifth inner cylinder (36) mounted concentrically with the fourth cylinder (31) at the lower end of the fourth cylinder (31) in a leak tight manner, where the assembly consisting of the ring shaped piston (32), the fourth inner cylinder (35) and the cylinder end (34) is adapted to reciprocate inside the fourth cylinder (31), inside the third inner cylinder (33) and outside the fifth inner cylinder (36) in a leak tight manner - a sixth volume (V6), filled with hydraulic fluid, located between the cylinder end (34), the inside of the fourth inner cylinder (35), the fifth inner cylinder (36) and the lower end of the fourth cylinder (31)

- a seventh volume (V7), filled with hydraulic fluid, located between cylinder end (34), the outside of the fourth inner cylinder (35), the inside of the third inner cylinder (33) and the upper end of the fourth cylinder (31)

- an eighth volume (V8), filled with hydraulic fluid, located between the ring shaped piston (32), the outside of the fifth inner cylinder (36) and the lower end of the fourth cylinder (31) - a ninth volume (V9), filled with gas at any pressure, located between the inside the fourth cylinder (31), the upper end of the fourth cylinder (31), the outside of the third inner cylinder (33), the outside of the fourth inner cylinder (35) and the upper end of the ring shaped piston (32)

- a second gas accumulator (60), consisting of a seventh cylinder (61) and a fifth piston (62), adapted for reciprocation with respect thereto

- a fourteenth volume (V14), filled with hydraulic fluid, located between the upper end of the seventh cylinder (61) and the upper end of the fifth piston (62)

- an fifteenth volume (V15), filled with gas at any pressure, located between the lower end of the seventh cylinder (61) and the lower end of the fifth piston (62)

- a conduit means between the first volume (V1) and the eighth volume (V8)

- conduit means between the sixth volume (V6) and the seventh volume (V7) adapted with a first hydraulic pump (P1) adapted to transport oil under pressure between the respective volumes

- a conduit means between the fourteenth volume (V14) and the seventh volume (V7) adapted with a third control valve (CV3)

- a conduit means between the fourteenth volume (V14) and the sixth volume (V6) adapted with a second control valve (CV2)

- a sensing means adapted for measuring the position of the first piston (12)

- a sensing means adapted for measuring the motion of the active heave compensator (100) - one or more sensing means adapted for measuring the pressure in one or more volume - a computer adapted for controlling the first hydraulic pump (P1) and the control valves based on input from the sensing means

- a set of tanks (T1, T2, …,TN), adapted for gas storage, where the number of tanks is minimum one

- a set of conduit means between each tank (T1, T2, …,TN) and the ninth volume (V9), with a set of control valve means (CVA1, CVA2, …,CVAN) in each conduit means adapted for connecting each tank (T1, T2, …,TN) individually to the ninth volume (V9)

- a gas booster (40), consisting of a fifth cylinder (41) and third piston (42), adapted for reciprocation with respect thereto

- a first gas accumulator (50), consisting of a sixth cylinder (51) and fourth piston (52), adapted for reciprocation with respect thereto

- a tenth volume (V10), filled with gas under any pressure, located between the upper end of the fifth cylinder (41) and the upper end of the third piston (42)

- an eleventh volume (V11), filled with hydraulic fluid, located between the lower end of the fifth cylinder (41) and the lower end of the third piston (42)

- a twelfth volume (V12), filled with hydraulic fluid, located between the lower end of the sixth cylinder (51) and the lower end of the fourth piston (52)

- a thirteenth volume (V13), filled with hydraulic fluid, located between the upper end of the sixth cylinder (51) and the upper end of the fourth piston (52)

- conduit means between the eleventh volume (V11) and the twelfth volume (V12) adapted with a second hydraulic pump (P2) adapted for transporting hydraulic fluid under pressure between the respective volumes

- a set of conduit means between each tank (T1, T2, …,TN), the ninth volume (V9), the tenth volume (V10) and the surroundings, with a set of control valve means (CV4, CV5, CV6, CVB1, CVB2, …,CVBN) in each conduit means adapted for individually adjusting the pressure in all gas volumes, except the second volume (V2), the thirteenth volume (V13) and the fifteenth volume (V15)

- a control valve means (CV1) in the conduit means between the first volume (V1) and the eighth volume (V8), adapted for manipulating the flow area from zero to free flow

- communication means adapted to transfer signals between the vessel (102) and the active heave compensator (100), preferably with acoustic communication

- at least one wireless MRU (104, 105) adapted for transferring motion data to the active heave compensator (100)

- either a battery pack or an umbilical for energy supply

Wherein at least one of the components is constituted of a predetermined number of components arranged in a parallel or series connection in order to increase the effective capacity of that component of any type.

Figure 1 particular details:

- a first inner cylinder (15) is mounted concentrically inside the first cylinder (11) and connected with a leak tight connection to the upper end of the first cylinder - the piston rod (13) is hollow and has a sealing surface towards the inner cylinder (15) - a third volume (V3) is formed, filled with hydraulic fluid, located inside the piston rod (13), the first inner cylinder (15) and the upper end of the first cylinder

- further the active heave compensator (100) comprises

- a depth compensator (20) consisting of a second cylinder (21), a second inner cylinder (26) mounted concentrically with the second cylinder (21), connected to the upper end of the second cylinder (21) in a leak tight fashion, a second piston (22) located inside the second inner cylinder (26), a second piston rod (23) connected to the second piston (22) and adapted for reciprocation within the second inner cylinder (26), a third cylinder (24) mounted concentrically within the second cylinder (21) and connected to the second piston rod (23) via a cylinder-rod connector (25)

- an fourth volume (V4), filled with hydraulic fluid, located between the upper end of the second piston (22), the inside of the second inner cylinder (26) and the upper end of the second cylinder (21)

- a fifth volume (V5), filled with gas under any pressure, located between the inside of the first cylinder (21), the inside of the third cylinder (24), the inside of the second inner cylinder (26), the lower side of the second piston (22) and the rod-cylinder connector (25) - wherein the rod-cylinder connector (25) as well as the third cylinder (24) is exposed to external pressure which will generate a higher pressure in the fourth volume (V4)

Figure 2 particular details:

- a set of conduit means between each tank (T1, T2, …,TN) and the second volume (V2), with a set of control valve means (CVC1, CVC2, …,CVCN) in each conduit means adapted for individually connecting any tank to the second volume (V2)

- a set of conduit means between each tank (T1, T2, …,TN), the ninth volume (V9), the tenth volume (V10) and the surroundings, with a set of control valve means (CV4, CV5, CV6, CV7, CVB1, CVB2, …,CVBN) in each conduit means adapted for individually adjusting the pressure in all gas volumes, except the thirteenth volume (V13) and the fifteenth volume (V15).

Table 1

Claims

Claims

One active heave compensator (100) comprising

a hydraulic actuator (10) and an accumulator (30), where the actuator (10) comprises a first cylinder (11) having an upper end and a lower end, a first piston rod (13) connected to a first piston (12) and extending downwardly therefrom through the lower end of the first cylinder (11), adapted for reciprocation with respect thereto, connection means (14) mounted at the upper and lower end of the hydraulic actuator (10) adapted for connecting the active heave compensator (100) to a floating object, like a vessel (102) mounted crane, and a payload (101);

a first volume (V1), filled with hydraulic fluid, located between the first piston (12) and the lower end of the first cylinder (11);

a second volume (V2), filled with gas at any pressure including zero, located between the first piston (12) and the upper end of the first cylinder (11);

characterized in that the accumulator (30) is a double acting gas accumulator (30), comprising of a fourth cylinder (31), a ring shaped piston (32) mounted concentrically within the fourth cylinder (31) and adapted for reciprocation with respect thereto, where the lower end of the ring shaped piston (32) is on the same side as the lower end of the fourth cylinder (31) when ring shaped piston (32) is at zero stroke, a third inner cylinder (33) mounted concentrically within the fourth cylinder (31) and fixed to the upper end of the fourth cylinder (31) with a leak tight connection, a fourth inner cylinder (35) mounted concentrically inside the fourth cylinder (31) and connected with an end to the upper end of the ring shaped piston (32) with a leak tight connection, a cylinder end (34) mounted concentrically within the fourth cylinder (31) at the opposite end of the fourth inner cylinder (35) with a leak tight connection, a fifth inner cylinder (36) mounted concentrically with the fourth cylinder (31) at the lower end of the fourth cylinder (31) in a leak tight manner, where the assembly consisting of the ring shaped piston (32), the fourth inner cylinder (35) and the cylinder end (34) is adapted to reciprocate inside the fourth cylinder (31), inside the third inner cylinder (33) and outside the fifth inner cylinder (36) in a leak tight manner;

a sixth volume (V6), filled with hydraulic fluid, located between the cylinder end (34), the inside of the fourth inner cylinder (35), the fifth inner cylinder (36) and the lower end of the fourth cylinder (31);

a seventh volume (V7), filled with hydraulic fluid, located between cylinder end (34), the outside of the fourth inner cylinder (35), the inside of the third inner cylinder (33) and the upper end of the fourth cylinder (31);

an eighth volume (V8), filled with hydraulic fluid, located between the ring shaped piston (32), the outside of the fifth inner cylinder (36) and the lower end of the fourth cylinder (31); a ninth volume (V9), filled with gas at any pressure, located between the inside the fourth cylinder (31), the upper end of the fourth cylinder (31), the outside of the third inner cylinder (33), the outside of the fourth inner cylinder (35) and the upper end of the ring shaped piston (32);

a second gas accumulator (60), consisting of a seventh cylinder (61) and a fifth piston (62), adapted for reciprocation with respect thereto;

a fourteenth volume (V14), filled with hydraulic fluid, located between the upper end of the seventh cylinder (61) and the upper end of the fifth piston (62);

an fifteenth volume (V15), filled with gas at any pressure, located between the lower end of the seventh cylinder (61) and the lower end of the fifth piston (62);

a conduit means between the first volume (V1) and the eighth volume (V8);

conduit means between the sixth volume (V6) and the seventh volume (V7) adapted with a first hydraulic pump (P1) adapted to transport oil under pressure between the respective volumes;

a conduit means between the fourteenth volume (V14) and the seventh volume (V7) adapted with a third control valve (CV3);

a conduit means between the fourteenth volume (V14) and the sixth volume (V6) adapted with a second control valve (CV2);

a sensing means adapted for measuring the position of the first piston (12);

a sensing means adapted for measuring the motion of the active heave compensator (100); one or more sensing means adapted for measuring pressure;

a computer adapted for controlling the first hydraulic pump (P1) and the control valves based on input from the sensing means.
2. Active heave compensator (100) according to claim 1, further comprising:

a set of tanks (T1, T2, …,TN), adapted for gas storage, where the number of tanks is minimum one;

a set of conduit means between each tank (T1, T2, …,TN) and the ninth volume (V9), with a set of control valve means (CVA1, CVA2, …,CVAN) in each conduit means adapted for connecting each tank (T1, T2, …,TN) individually to the ninth volume (V9).
3. Active heave compensator (100) according to claim 1 or 2, further comprising:

a gas booster (40), consisting of a fifth cylinder (41) and third piston (42), adapted for reciprocation with respect thereto;

a first gas accumulator (50), consisting of a sixth cylinder (51) and fourth piston (52), adapted for reciprocation with respect thereto;

a tenth volume (V10), filled with gas under any pressure, located between the upper end of the fifth cylinder (41) and the upper end of the third piston (42);

an eleventh volume (V11), filled with hydraulic fluid, located between the lower end of the fifth cylinder (41) and the lower end of the third piston (42);

a twelfth volume (V12), filled with hydraulic fluid, located between the lower end of the sixth cylinder (51) and the lower end of the fourth piston (52);

a thirteenth volume (V13), filled with hydraulic fluid, located between the upper end of the sixth cylinder (51) and the upper end of the fourth piston (52);

conduit means between the eleventh volume (V11) and the twelfth volume (V12) adapted with a second hydraulic pump (P2) adapted for transporting hydraulic fluid under pressure between the respective volumes.

Active heave compensator (100) according to at least one of claim 1-3, further comprising: a set of conduit means between each tank (T1, T2, …,TN), the ninth volume (V9), the tenth volume (V10) and the surroundings, with a set of control valve means (CV4, CV5, CV6, CVB1, CVB2, …,CVBN) in each conduit means adapted for individually adjusting the pressure in all gas volumes, except the second volume (V2), the thirteenth volume (V13) and the fifteenth volume (V15).

Active heave compensator (100) according to at least one of claim 1-4, further comprising: a set of conduit means between each tank (T1, T2, …,TN) and the second volume (V2), with a set of control valve means (CVC1, CVC2, …,CVCN) in each conduit means adapted for individually connecting any tank to the second volume (V2);

a set of conduit means between each tank (T1, T2, …,TN), the ninth volume (V9) and the surroundings, with a set of control valve means (CV
4, CV
5, CV
6, CV
7, CVB1, CVB2, …,CVBN) in each conduit means adapted for individually adjusting the pressure in all gas volumes, except the thirteenth volume (V13) and the fifteenth volume (V15).

Active heave compensator (100) according to at least one of claim 1-5, further comprising: a control valve means (CV1) in the conduit means between the first volume (V1) and the eighth volume (V8), adapted for manipulating a flow area from zero to free flow.

Active heave compensator (100) according to at least one of claim 1-6, wherein

a first inner cylinder (15) is mounted concentrically inside the first cylinder (11) and connected with a leak tight connection to the upper end of the first cylinder;

the piston rod (13) is hollow and has a sealing surface towards the inner cylinder (15); a third volume (V3) is formed, filled with hydraulic fluid, located inside the piston rod (13), the first inner cylinder (15) and the upper end of the first cylinder;

further the active heave compensator (100) comprises:

a depth compensator (20) consisting of a second cylinder (21), a second inner cylinder (26) mounted concentrically with the second cylinder (21), connected to the upper end of the second cylinder (21) in a leak tight fashion, a second piston (22) located inside the second inner cylinder (26), a second piston rod (23) connected to the second piston (22) and adapted for reciprocation within the second inner cylinder (26), a third cylinder (24) mounted concentrically within the second cylinder (21) and connected to the second piston rod (23) via a cylinder-rod connector (25);

an fourth volume (V4), filled with hydraulic fluid, located between the upper end of the second piston (22), the inside of the second inner cylinder (26) and the upper end of the second cylinder (21);

a fifth volume (V5), filled with gas under any pressure, located between the inside of the second cylinder (21), the inside of the third cylinder (24), the inside of the second inner cylinder (26), the lower side of the second piston (22) and the rod-cylinder connector (25); wherein the rod-cylinder connector (25) as well as the third cylinder (24) is exposed to external pressure which will generate a higher pressure in the fourth volume (V4).
8. Active heave compensator (100) according to at least one of claim 1-7, further comprising:

communication means adapted to transfer signals between the vessel (102) and the active heave compensator (100), preferably with acoustic communication.
9. Active heave compensator (100) according to at least one of claim 1-8, further comprising:

at least one wireless MRU (104, 105) adapted for transferring motion data to the active heave compensator (100).
10. Active heave compensator (100) according to at least one of claim 1-9, wherein the active heave compensator (100) is powered either by a battery pack or an umbilical.
11. Active heave compensator (100) according to any one of claims 1-10, wherein at least one of the components is constituted of a predetermined number of components arranged in a parallel or series connection in order to increase the effective capacity of that component of any type.