NO20160771A1

NO20160771A1 - Semi active inline heave compensator

Info

Publication number: NO20160771A1
Application number: NO20160771A
Authority: NO
Inventors: Tord Martinsen
Original assignee: Safelink As
Priority date: 2016-05-08
Filing date: 2016-05-08
Publication date: 2017-11-09
Also published as: NO347769B1

Description

INLINE SEMI ACTIVE HEAVE COMPENSATOR

The inline semi active heave compensator (ISAHC) 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 like a bange, but not limited only thereto. The ISAHC is designed to operate in air or in water. The ISAHC 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-damping device if the active component fails.

BACKGROUND OF THE INVENTION

Many prior art active heave compensators exist, like the one described in e.g. US 2010/0057279 A1. One of the differences between the prior art and the invention is for example that the ISAHC is a mobile compensator for inline use with a passive backup system to go subsea with the payload being installed, while traditional active compensators often do not have a passive backup system and always stay topside on an installation vessel.

The main disadvantages of the prior art are: high capital binding in permanent 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 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 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, reduced wear of the steel wire rope, low energy consumption. However, the compensator uses some of the available lifting height, and it is required to pre-set the compensator before usage. Furthermore, when using a battery pack for the compensator, there could be some limited usable compensation time per lift.

The ISAHC is based on a previous patent application, inline active heave compensator (IAHC), with variations in hydraulic transportation means location and space requirements as well as improved compensation efficiency. This application mainly focuses on the elements not covered in the previous application.

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 ISAHC is a semi active heave compensator for inline usage topside and subsea. It has numerous advantages compared to traditional semi active heave compensators.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1-2 are schematic illustrations of two versions or embodiments of the ISAHC according to the present invention in which the major component parts of the ISAHC are speciflcally identified. Figure 1 illustrates a version orembodiment of an inline semi active heave compensator (ISAHC

(100)) where the means for hydraulic fluid transportation (17) is connected between the oil side of the first cylinder (1) and the oil side of the second cylinder (8). This removes the need for a separate accumulator for the active part of the compensator. The downside to this is that the means for hydraulic fluid transportation (17) has to operate at high pressure, which has two consequences; One, its unfeasible to use a pressure intensifier to increase flow rate, which in turn requires large flow for langer designs, in practice this means several means for hydraulic fluid transportation (17) in parallel, which will increase cost; Two, a significant amount of oil will leak from the drain port of the means for hydraulic fluid transportation (17) while its pressurized, this can be countered by a secondary pump to transport it back and by using valves in the conduit means (7, 28) to disconnectthe means for hydraulic fluid transportation (17) from the hydraulic pressure (not shown) when it's not in use. Main use of this design seems to be for smaller compensators, where one pump gives high enough flow, combined with valves to disconnect the hydraulic pressure.

Figure 2 illustrates a version or embodiment of an inline semi active heave compensator (ISAHC

(100)) where a pressure intensifier (24, 25, 26,27) is used to increase the flow rate of the means for hydraulic fluid transportation (17). The flow is increased by a factor equal to the square of the diameter ratio between the fourth piston (26) and the second piston rod (26), which can be in the range 1.1-40. The fourth piston can also be used to indirectly determine the position of the first piston (2) using a third piston position sensor (19). The compensator (100) is fitted with a means for distance measurement (31), suitable for measuring the distance to the seabed (106), which can be helpful in improving efficiency of the compensator (100). The compensator (100) is also fitted with a means for communication (30), which is suited for communicating with the crane on the vessel

(102), mainly giving MRU readings (MRU located in crane tip) and winch speed to the compensator

(100) computer so that it can react faster to operator action (i.e. spooling of wire rope) and increase efficiency. This version of the compensator (100) is well suited for large designs and applications where rapid response is required. Figure 3 shows a placement of the ISAHC in a subsea lift, wherein it is located right above a payload, which is symbolized with a rectangle. Figure 4 is an illustration of a prior art active heave compensator, permanently installed topside.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 illustrates a version or embodiment of an inline semi active heave compensator (ISAHC

(100)). This will now be described in detail. The ISAHC (100) is normally rigged to a work wire coming from the vessel (102) at eitherthe second means of connection (4), where the second means of connection (4) is facing down, or the first means of connection (5), where the first means of connection (5) is facing up. The means of connection (either4 or 5) not connected to the vessel

(102) is connected to the payload (101). If necessary ordesired, any one of the connection means (4, 5) can be connected to both the vessel (102) and the payload (101). The connection means (4, 5) can be at least one of: a padeye and a clevis, but not limited only thereto. The first cylinder (1) contains a first piston (2). A first piston rod (3) extends from the first piston (2) located within the first cylinder (1) through the lower end (4) thereof. The first cylinder (1) contains a first volume, filled with hydraulic fluid, located between the first piston (2) and the lower end (4) of the first cylinder (1). The first cylinder (1) also contains a second volume, with no content (vacuum), located between the first piston (2) and the upper end (5) of the first cylinder (1). A first piston position sensor (6) may be present in the first cylinder (1). The first piston position sensor (6) can be used to directly calculate the position of at least one of: the first piston (2) and the first piston rod (3), relative to at least one of the upper and lower ends of the first cylinder (1).

The second cylinder (8) contains a second piston (9) separating a third volume, filled with hydraulic fluid, located between the lower end of the second cylinder (8) and the second piston (9), as well as a fourth volume, filled with gas, located between the upper end of the second cylinder (8) and the second piston (9). A second piston position sensor (10) can be used to indirectly calculate the position of at least one of: the first piston (2) and the first piston rod (3), relative to at least one of the upper and lower ends of the first cylinder (1). The gas pressure in the fourth volume in the second cylinder (8) effectively pressurizes the first volume in the first cylinder (1) via conduit means (7, 28) connecting the lower sides of the first (1) and the second (8) cylinder, as well as the third volume in the second cylinder (8). A means for hydraulic fluid transportation (17) is connected between the oil side of the first cylinder (1) and the oil side of the second cylinder (8). Valves may also be present in the conduit means (28, 7), this is not shown in the figure. An energy source (16) powers the means for hydraulic fluid transportation, and may be a large battery pack or an umbilical. An accelerometer (29) and/or a pressure sensor for external pressure (not shown), combined with a position sensor (6,10) is used to control the means for hydraulic fluid transportation (17).

Figure 2 illustrates another version or embodiment of an inline semi active heave compensator (ISAHC (100)). This will now be described in detail. The ISAHC (100) is normally rigged to a work wire coming from the vessel (102) at eitherthe second means of connection (4), where the second means of connection (4) is facing down, or the first means of connection (5), where the first means of connection (5) is facing up. The means of connection (either4 or 5) not connected to the vessel

(102) is connected to the payload (101). If necessary ordesired, any one of the connection means (4, 5) can be connected to both the vessel (102) and the payload (101). The connection means (4, 5) can be at least one of: a padeye and a clevis, but not limited only thereto. The first cylinder (1) contains a first piston (2). A first piston rod (3) extends from the first piston (2) located within the first cylinder (1) through the lower end (4) thereof. The first cylinder (1) contains a first volume, filled with hydraulic fluid, located between the first piston (2) and the lower end (4) of the first cylinder (1). The first cylinder (1) also contains a second volume, filled with hydraulic fluid, located between the first piston (2) and the upper end (5) of the first cylinder (1). A first piston position sensor (6) may be present in the first cylinder (1). The first piston position sensor (6) can be used to directly calculate the position of at least one of: the first piston (2) and the first piston rod (3), relative to at least one of the upper and lower ends of the first cylinder (1).

The second cylinder (8) contains a second piston (9) separating a third volume, filled with hydraulic fluid, located between the lower end of the second cylinder (8) and the second piston (9), as well as a fourth volume, filled with gas, located between the upper end of the second cylinder (8) and the second piston (9). A second piston position sensor (10) can be used to indirectly calculate the position of at least one of: the first piston (2) and the first piston rod (3), relative to at least one of the upper and lower ends of the first cylinder (1).The gas pressure in the fourth volume in the second cylinder (8) effectively pressurizes the first volume in the first cylinder (1) via conduit means (7) connecting the lower sides of the first (1) and the second (8) cylinder, as well as the third volume in the second cylinder (8).

The third cylinder (25) contains a third piston (26) and a fifth volume, filled with hydraulic fluid, located between the third piston (26) and the upper end of the third cylinder (25), as well as a sixth volume, filled with low pressure gas, located between the third piston (26) and the lower end of the third cylinder (25). A second piston rod (26) is connected to the third piston (26) and extends through the lower end of the third cylinder (25) into a fourth cylinder (24). The fourth cylinder (24) contains a seventh volume, filled with hydraulic fluid, located around the second piston rod (26) and the fourth cylinder (24). A third piston position sensor (19) may be present in the third cylinder (25) or fourth cylinder (26). The third piston position sensor (19) can indirectly measure the position of the first piston (2). The area ratio between piston (27) and rod (26) acts like a pressure intensifier, which effectively multiplies the oil flow coming from the means for hydraulic fluid transportation (17). This is needed due to high required flow rate at low pressure, while commercially available reversible pumps give high pressure at low flow.

The fifth cylinder (22) contains a fourth piston (20). The fifth cylinder (22) contains an eighth volume, filled with gas, located between the fourth piston (20) and the lower end of the fifth cylinder (22), as well as a ninth volume, filled with hydraulic fluid, located between the fourth piston (20) and the upper end of the fifth cylinder (22). The gas pressure in the eighth volume in the third cylinder (22) effectively pressurizes hydraulic fluid in the ninth volume in the fifth cylinder (22). The fifth volume is connected to the second volume via conduit means (21), and they have the same pressure;

The pressure in the hydraulic fluid in the seventh volume in the fourth cylinder (24) is not necessarily equal to the pressure of the hydraulic fluid in the ninth volume in the fifth cylinder (22), because the means for hydraulic fluid transportation (17) can transport hydraulic fluid between the two volumes, via conduit means (18,23) and create a positive or a negative pressure deviation between them. Valves may also be present in the conduit means (18, 23), this is not shown in the figure. An energy source (16) powers the means for hydraulic fluid transportation, and may be a large battery pack or an umbilical connected to the vessel (102). An accelerometer (29) and/or a pressure sensor for external pressure (not shown), and/or a means for distance measurement (31), and/or a means for communication (30) with the MRU located in the crane tip (not shown), combined with a position sensor (6,10,19) is used to control the means for hydraulic fluid transportation (17).

The gas pressures in all gas volumes may be adjusted by a means forgås transportation (not shown).

It is possible to con neet multiple cylinders in parallel and series to achieve the same basic functionality (not shown).

It is also possible to control the means for hydraulic fluid transportation (17) håving in mind that the net force on the payload should be constant. This can be achieved by regulating the pressure on the upper side of the first piston (2). When the pressure on the lower side of the first piston (2) increases due to gas compression, the pressure on the upper side of the first piston (2) will simultaneously increase, so that the net force will be zero.

The means for hydraulic fluid transportation (17) can be at least one reversible hydraulic pump driven by an electric motor.

The hydraulic fluid can normally be a mineral oil or a glycol-water fluid, but not limited only thereto.

Claims

1. Inline semi active heave compensator (100) comprising: a first cylinder (1) håving an upper end and a lower end; a first connection means (5) mounted at the upper end of the first cylinder (1) and adapted for connecting the first cylinder (1) to at least one of: a vessel (102) at sea surface and a payload (101); a first piston (2) located within the first cylinder (1) and adapted for reciprocation with respect thereto; a first piston rod (3) connected to the first piston (2) and extending downwardly therefrom through the lower end of the first cylinder (1); a second connector means (4) adapted for securing the first piston rod (3) to at least one of: the vessel (102) at the sea surface and the payload (101), and located at the lower end of the first cylinder (1); a first volume, filled with hydraulic fluid, located between the first piston (2) and the lower end of the first cylinder (1); a second volume, located between the first piston (2) and the upper end of the first cylinder (1); a second cylinder (8) containing a second piston (9); a third volume of hydraulic fluid located between the lower end of the second cylinder (8) and the second piston (9); a sensing arrangement (6 or 10 or 19) adapted for direct or indirect measuring the position of at least one of: the first piston (2) and the first piston rod (3), relative to at least one of: the lower and upper ends of the first cylinder (1); a means for hydraulic fluid transportation (17) adapted for transporting hydraulic fluid between two volumes; an accelerometer (29) integrated into the compensator (100) and adapted to measure movement of the compensator (100); where the means for hydraulic fluid transportation (17) is controlled based on the direct or indirect measurements from both the sensing arrangement (6 or 10 or 19) and the accelerometer (29).

2. Inline semi active heave compensator (100) according to claim 1, where the second volume is under vacuum; a means for hydraulic fluid transportation (17) adapted for transporting hydraulic fluid between the first and third volume, using conduit means (7, 28), and create a positive or a negative pressure deviation between the two volumes; valves may also be present in the conduit means (7, 28), to bypass the means for hydraulic fluid transportation (17) or to block it off.

3. Inline semi active heave compensator (100) according to claim 1, where the second volume is filled with hydraulic fluid.

4. Inline semi active heave compensator (100) according to claim 1 and 3, further comprising: a third cylinder (25) contains a third piston (26) and a fifth volume, filled with hydraulic fluid, located between the third piston (26) and the upper end of the third cylinder (25), as well as a sixth volume, filled with low pressure gas, located between the third piston (26) and the lower end of the third cylinder (25); the fifth volume is connected to the second volume via conduit means (21), and they have the same pressure; a second piston rod (26) is connected to the third piston (26) and extends through the lower end of the third cylinder (25) into a fourth cylinder (24); a fourth cylinder (24) contains a seventh volume, filled with hydraulic fluid, located around the second piston rod (26) and the fourth cylinder (24); a fifth cylinder (22) contains a fourth piston (20); a fifth cylinder (22) contains an eighth volume, filled with gas, located between the fourth piston (20) and the lower end of the fifth cylinder (22), as well as a ninth volume, filled with hydraulic fluid, located between the fourth piston (20) and the upper end of the fifth cylinder (22); the gas pressure in the eighth volume in the third cylinder (22) effectively pressurizes hydraulic fluid in the ninth volume in the fifth cylinder (22); a means for hydraulic fluid transportation (17) can transport hydraulic fluid between the seventh and ninth volume, via conduit means (18, 23) and create a positive ora negative pressure deviation between them; valves may also be present in the conduit means (18, 23), to bypass the means for hydraulic fluid transportation (17) or to block it off.

5. Inline semi active heave compensator (100) according to any one of claims 1 -4, further comprising: a motion reference unit (MRU) placed in a crane tip (not shown); a means for distance measurement (31), adapted for measuring distance between the compensator (100) and the seabed (106); a means for communication (30), adapted for providing MRU data to the compensator (100).

6 Inline semi active heave compensator (100) according to any one of claims 1 -5, wherein the means for hydraulic fluid transportation (17) is at least one reversible hydraulic pump being driven by an electric motor.

7. Inline semi active heave compensator (100) according to any one of claims 1 -6, further comprising an energy source (16) being at least one battery pack within the compensator (100).

8. Inline semi active heave compensator (100) according to any one of claims 1 -7, wherein an energy source (16) on the vessel (102) is connected to the compensator (100) via an umbilical.

9. Inline semi active heave compensator (100) according to any one of claims 1 -8, wherein at least one of the cylinders is constituted of a predetermined numberof cylinders 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.