Multi function heave compensator

Abstract

A heave compensator with adjustable dampening properties includes a length extension device having an inner space divided by a slide-able piston into a vacuum chamber and a liquid filled chamber, a gas accumulator divided by a slide-able piston into a gas filled chamber and a liquid filled chamber, and a gas tank having an expansion chamber. The liquid and gas chamber are fluidly connected to each other with valve controlled conduits. Further, the device includes pressure and temperature sensors that register pressure and temperature in the gas and liquid phases. The device further includes a control unit having a signal receiving unit, a writeable computer memory, a data processing unit, and a signal transmitting unit. The data processing unit contains computer software that calculates suited amounts of gas and gas pressure in the gas accumulator and/or gas tank based on the information of which lifting operation is going to be performed. The data processing unit further engages activation means such that the suited amount of gas and gas pressure are achieved and maintained during the different phases of the lifting operation.

Claims

1. A device for compensating for heave movements between a lifting device and a load lifted by the lifting device, the device comprising: an elongated length extension device comprising: a closed upper end; a lower end having an opening for a piston rod and a liquid outlet; an inner space divided by a slide-able first piston into an upper vacuum chamber and a first lower liquid filled chamber; a piston rod of length at least equal to the length of the length extension device, wherein a first end of the piston rod is attached to the first piston, and wherein the piston rod stretches through the first liquid filled chamber and further out through the opening in the lower end of the length extension device; means arranged at a second end of the piston rod for releasable attachment of the load; and means arranged at the upper end of the length extension device for releasable attachment of the lifting device; an elongated cylindrical gas accumulator comprising: an upper end having a first adjustable gas outlet, the first adjustable gas outlet having a first valve; a lower end having a liquid outlet; and an inner space divided by a slide-able second piston into an upper chamber and a second lower liquid filled chamber, an adjustable liquid transferring device fluidly connected to the liquid outlet of the lower end of the length extension device and the liquid outlet of the lower end of the cylindrical gas accumulator, the adjustable liquid transferring device having a second valve; an activator for selective opening or closing of one or both of the first valve and the second valve; a first and second pressure and temperature sensor for measuring a temperature and/or pressure of the liquid in at least one of the first lower liquid filled chamber and the second lower liquid filled chamber and the gas in the upper chamber of the cylindrical gas accumulator, respectively; a position sensor for measuring the position of the first piston; and a control unit comprising: a signal receiver unit and data storage memory for registering the measured temperatures and/or pressures of the liquid in one of or both of the first lower liquid filled chamber and the second lower liquid filled chamber, the gas in the upper gas filled chamber of the cylindrical gas accumulator, and the position of the first piston; a signal treatment unit for calculating a real equilibrium position of the first piston from the registered temperatures and/or pressures and the registered positions of the first piston; a data processing unit for calculating an amount of gas that needs to be ventilated out of the first adjustable gas outlet in order to obtain an intended equilibrium position of the first piston; and a signal transmission unit engaging the activator of the first valve and/or the second valve such that the intended amount of gas exits through the first adjustable gas outlet and such that the first piston obtains the intended equilibrium position.

2. The device according to claim 1, further comprising: a gas tank comprising: an upper end having a second adjustable gas outlet, the second adjustable gas outlet having a third valve; a closed lower end; and an expansion chamber; a third pressure and temperature sensor for measuring the temperature and/or pressure of the gas in the expansion chamber of the gas tank; a gas transferring device fluidly connected to the first adjustable gas outlet and the second adjustable gas outlet, the gas transferring device having a third adjustable gas outlet that opens to an environment surrounding the device, wherein the third adjustable gas outlet has a fourth valve; and the activator may selectively open or close one or both of the third valve and the fourth valve, wherein the signal receiver unit receives signals from the first, second, and third pressure and temperature sensor and the position sensor, wherein the data processing unit contains computer software with instructions, wherein the computer software calculates the amount of gas present in the upper gas filled chamber and/or the expansion chamber by use of a gas equation of state and the registered temperatures and/or pressures, wherein the signal transmission unit transmits guidance signals to the activator of one or more of the first, second, third, or fourth valve, and wherein the data processing unit of the control unit contains one or more computer software modules each having a set of instructions that calculate, according to a wanted compensation functionality, a wanted amount of gas in the upper chamber of the cylindrical gas accumulator and/or the expansion chamber of the gas tank, and which activates the signal transmission unit such that the wanted amount of gas in the upper chamber of the cylindrical gas accumulator and/or the expansion chamber of the gas tank is obtained.

3. The device according to claim 2, wherein: the length extension device is an elongated cylinder having an elongated inner space, wherein: the means for attachment of the length extension device to the lifting device comprises a hook located on the outside of the first end of the length extension device; the piston rod is arranged in parallel with the centre axis of the length extension device; and the opening in the second end of the length extension device is adapted to form a fluid tight closure around the piston rod; the gas accumulator is an elongated cylinder having the inner space that is elongated and divided by the slide-able piston of the gas accumulator into the upper chamber that is a first gas filled chamber and the second lower liquid filled chamber; and the first, second, and third pressure and temperature sensors are a combined pressure and temperature sensor, or a separate pressure sensor and separate temperature sensor.

4. The device according to claim 2, wherein at least one of the liquid outlet of the lower end of the length extension device, the first adjustable gas outlet, the second adjustable gas outlet, or the third adjustable gas outlet has a by-pass conduit across the first, second, third, or fourth valve of the conduit equipped with a pressure compensating valve that are engaged individually by the activator via the signal transmission unit of the control unit.

5. The device according to claim 2, the device further comprising: a fifth valve with activator located downstream from the fourth valve on the third adjustable gas outlet.

6. The device according to claim 2, wherein the signal treatment unit further comprises: a filter that reduces or removes signal noise in the signals from one or more of the first, second, third, and fourth pressure and temperature sensor; and a filter that filters out cyclic movements in the signal from the position sensor and estimates the equilibrium position of the first piston.

7. The device according to claim 2, wherein the control unit further comprises: a signal transmitter/receiver that enables transmission of acoustic, electric, or electromagnetic guidance signals to and from the data processing unit of the control unit of the device; and an external guidance unit, an operator, or a remotely operated vehicle (ROV).

8. The device according to claim 7, wherein the signal transmitter/receiver is a radio transmitter/receiver.

9. The device according to claim 2, wherein: the expansion chamber of the gas tank is pre-stored with sufficient amount of gas under high pressure to at least be able to push the first piston of the length extension device up to the first end of the length extension device when the pressure in the expansion chamber of the gas tank and the upper chamber of the cylindrical gas accumulator are equalized by allowing the gas to flow freely between the expansion chamber of the gas tank and the upper chamber of the cylindrical gas accumulator; and the data processing unit additionally comprises: a quick lift computer program module containing data instructions, wherein when the data instructions of the quick lift computer program are executed in the data processing unit, the data processing unit performs a method comprising: receiving a signal for executing the quick lift computer program module; and opening the first valve and the third valve.

10. The device according to claim 9, wherein the data processing unit further comprises: a weight compensating computer program module containing data instructions, wherein when the data instructions of the weight compensating computer module are executed in the data processing unit, the data processing unit performs the method further comprising: controlling that the first, the second, and the third valves are closed and that the second valve is open; continuously registering the signal from the position sensor and the second pressure and temperature sensor; awaiting an execution signal for the weight compensating computer program, and when the execution signal is received, awaiting a predetermined time, and then calculating the equilibrium position of the first piston from the registered position data from the position sensor, and employing this value together with the pressure and temperature values from the second pressure and temperature sensor in the following equation: $m_i^{\mathrm{acc}}=\frac{P_i^{\mathrm{acc}}\left(V_{\mathrm{acc}}-A_o{S}_i\right)}{T_i^{\mathrm{acc}}{R}_{N2}}$ to calculate the desired amount of gas in the cylindrical gas accumulator (m.sub.sp.sup.acc) and thereafter continuously calculating the present amount of gas in the cylindrical gas accumulator (m.sub.k.sup.acc);  opening the first valve and the fourth valve;  calculating Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc; and  when |Δm.sub.sp|<K, where K is a predetermined stop criterion, closing the first valve and the fourth valve.

11. The device according to claim 10, wherein the data processing unit further comprises: a landing compensation computer program module containing data instructions, wherein when the data instructions of the landing compensation computer program module are executed in the data processing unit, the data processing unit performs a method comprising: upon receiving a signal from an operator to initiate the landing compensation computer program module, determining the desired pressure (p.sub.sp.sup.acc) of the gas phase in the expansion chamber of the gas tank by reading the actual pressure (p.sub.k.sup.acc) in the cylindrical gas accumulator registered by second pressure and temperature sensor, and setting p.sub.sp.sup.acc=ƒ.Math.p.sub.k.sup.acc, where ƒε<0, 1>; continuously reading the signal from the position sensor; controlling that the first valve is closed, and thereafter opening the third and the fourth valves; closing the fourth valve when the desired pressure (p.sub.sp.sup.acc), of the gas phase is obtained; and upon receiving a signal from the operator to execute the landing compensation computer program module, opening the first valve.

12. The device according to claim 11, wherein ƒε<0.5, 0.95>, ƒΣ<0.6, 0.9> or ƒε<0.7, 0.8>.

13. The device according to claim 2, wherein the data processing unit further comprises: a lowering compensation computer program module containing data instructions, wherein when the data instructions of the lowering compensation computer program module are executed in the data processing unit, the data processing unit performs a method comprising: controlling that the second valve is open and that the first, third, and fourth valves are closed; continuously reading the signal from the position sensor; determining the desired pressure of the gas phase in the expansion chamber of the gas tank according to a predetermined estimate of the sensible weight of the load at the intended water depth; calculating the pressure of the liquid in the first lower liquid filled chamber needed to balance the tensile force on the first piston due to the sensible weight of the load, opening the third and fourth valves; and when the signal from the third pressure and temperature sensor shows that the pressure in the expansion tank of the gas tank has reached the desired pressure, closing the fourth valve.

14. The device according to claim 2, wherein the data processing unit further comprises: a depth compensation computer program module containing data instructions, wherein when the data instructions of the depth compensation computer program are executed in the data processing unit, the data processing unit performs a method comprising: controlling that the first, third, and fourth valves are closed and that the second valve is open; continuously registering the signal from the fourth pressure and temperature sensor and utilizing the signal to estimate the water depth; continuously reading the signal from the position sensor and the second pressure and temperature; and when the water depth has increased with a predetermined interval and the pressure of the surrounding water is less than 50% of the gas pressure inside the cylindrical gas accumulator, execute: awaiting a predetermined time, and then calculating the equilibrium position of the first piston from the registered position data from the position sensor and employing this value together with the pressure and temperature values from the second pressure and temperature sensor in the equation: $m_i^{\mathrm{acc}}=\frac{P_i^{\mathrm{acc}}\left(V_{\mathrm{acc}}-A_o{S}_i\right)}{T_i^{\mathrm{acc}}{R}_{N2}}$ to calculate the desired amount of gas in the cylindrical gas accumulator (m.sub.sp.sup.acc) and thereafter continuously calculate the amount of gas being present in the cylindrical gas accumulator (m.sub.k.sup.acc);  opening the first valve and the fourth valve and continuously calculating Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc; and  when |Δm.sub.sp|<K, where K is a predetermined stop criterion, closing the first valve and the fourth valve; or when the water depth has increased with a predetermined interval and the pressure of the surrounding water is larger than 50% of the gas pressure inside the cylindrical gas accumulator, execute: awaiting a predetermined time, and then calculating the equilibrium position of the first piston from the registered position data from the position sensor, and employing this value together with the pressure and temperature values from the second pressure and temperature sensor in the equation: $m_i^{\mathrm{acc}}=\frac{P_i^{\mathrm{acc}}\left(V_{\mathrm{acc}}-A_o{S}_i\right)}{T_i^{\mathrm{acc}}{R}_{N2}}$ to calculate the desired amount of gas in the cylindrical gas accumulator (m.sub.sp.sup.acc), and thereafter continuously calculating the present amount of gas in the cylindrical gas accumulator (m.sub.k.sup.acc);  opening the first valve and the third valve and continuously calculating Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc; and  when |Δm.sub.sp|<K, where K is a predetermined stop criterion, closing the first valve and the third valve.

15. The device according to claim 2, wherein the data processing unit further comprises: a reduction of spring resistance computer program module containing data instructions, wherein when the data instructions of the reduction of spring resistance computer program module are executed in the data processing unit, the data processing unit performs a method comprising: continuously registering the signal from the third pressure and temperature sensor and utilizing the signal to estimate the water depth; and when the water depth has reached a predetermined depth, opening the first valve and the third valve.

16. The device according to claim 2, wherein the data processing unit further comprises: a lock and release computer program module, wherein when the lock and release computer program module is executed in the data processing unit, the data processing unit performs a method comprising: upon receiving a locking signal from an operator, closing the second valve; and upon receiving a release signal from the operator, opening the second valve.

17. The device according to claim 2, wherein the data processing unit further comprises: a rapid landing compensation computer program module containing data instructions, wherein when the data instructions of the rapid landing compensation computer program module are executed in the data processing unit, the data processing unit executes: awaiting receiving signal to preparation of rapid landing compensation from an operator; upon receiving the signal to execute preparation of the rapid landing compensation, opening the first and third valves such that gas under high pressure flows from the expansion chamber of the gas tank and into the upper chamber of the cylindrical gas accumulator and the first piston is pushed towards the upper end of the length extension device; after a predetermined time period, closing the second and third valves; regulating thereafter the pressure in the cylindrical gas accumulator to the desired by continuously registering the signal from the position sensor and the second pressure and temperature sensor and using the registered position data from the position sensor to calculate the equilibrium position of the first piston, and utilizing this value together with the pressure and temperature values from the second pressure and temperature in an equation: $m_i^{\mathrm{acc}}=\frac{P_i^{\mathrm{acc}}\left(V_{\mathrm{acc}}-A_o{S}_i\right)}{T_i^{\mathrm{acc}}{R}_{N2}}$ to calculate the desired amount of gas (m.sub.sp.sup.acc) and thereafter continuously calculating the present amount of gas inside the cylindrical gas accumulator (m.sub.k.sup.acc); opening thereafter the fourth valve and continuously calculating Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc; when |Δm.sub.sp|<K, where K is a predetermined stop criterion, close the first and fourth valves; awaiting receiving signal to execute the rapid landing compensation from the operator, upon receiving the signal from the operator to execute the rapid landing compensation, opening the second valve.

18. The device according to claim 1, the device further comprising: at least two gas tanks fluidly connected to the gas filled upper chamber of the cylindrical gas accumulator by a gas manifold connecting a gas outlet of each of the at least two gas tanks to the first adjustable gas outlet.

19. The device according to claim 1, the device further comprising: at least two length extension devices, wherein the means for mechanical connection between the first slide-able piston of each of the at least two length extension devices and the suspended load are mechanically connected together to form a single unit equipped with the means for releasable attachment of the load.

20. The device according to claim 1, the device further comprising: a fourth pressure and temperature sensor that measures the pressure and/or temperature of an environment surrounding the device.

Description

LIST OVER FIGURES

(1) FIG. 1 is a schematic drawing seen from the side of an example embodiment of a heave compensator according to the invention.

(2) FIG. 2 is a schematic drawing seen from the side of a second example embodiment of a heave compensator according to the invention.

(3) FIG. 3 is a box diagram showing an example embodiment of the components of the control unit 110, and how they are connected together.

DESCRIPTION OF AN EXAMPLE EMBODIMENT OF THE INVENTION

(4) The present invention will be described in greater detail by way of example embodiments. The example embodiments are based on the heave compensator described in FIGS. 2 and 3, and shows examples of how the control unit 110 of the heave compensator obtains the different functionalities in practice. However, these should not be interpreted in a restricting sense; the present invention also comprises additional possible configurations (number of length extension devices, gas accumulators, and/or gas tanks) and other possible ways of adjusting the gas pressure in the system to obtain the intended effect.

Example Embodiment 1, Quick Lift

(5) This functionality is advantageous during lift of loads from a floating cargo vessel by a crane on another vessel, ashore etc., where wave induced motions of the cargo vessel involves a risk of re-contact between the load and vessel at the initial phase of the lift. The Quick lift is obtained by allowing piston 9 to be lowered towards the second end 3 of the length extension device and then allowing gas under a high pressure from the gas tank to flow into the gas accumulator to push piston 9 upward towards the first end 2 of the length extension device, and in this manner contributing to lift the load faster than the lifting crane may obtain alone. In this case, it is advantageous to balance two considerations, the need for avoiding re-contact by obtaining a sufficiently rapid safe lifting height of the load and the need for avoiding too heavy tensile strains on the load and/or the lifting device during the lift. It is thus advantageous if the heave compensator may execute the Quick lift without compromising too much of its ability to compensate for heave movements. This is obtained in practice by preventing the piston 9 to but against/come into contact with the lower end 3 of the length extension device such that heave movements may be compensated by a smooth and springy movement of piston 9.

(6) In practice, this may be achieved by pre-storing sufficient amount of gas in the upper chamber 22 of the gas accumulator 16 such that when the sensible weight of the load begins to pull piston 9 towards the lower end 3 and thus decreasing the volume of chamber 22, that a sufficient strong pressures arises in the chamber 22 to counteract the pressure in the liquid phase when the full sensible weight of the load is pulling on piston 9, when the piston 9 is pulled to a pre-determined distance above the lower end 3. The distance above the lower end 3 of which the piston 9 may be pulled down to, depends on the heave compensator being employed, the weight of the load, and/or the tensile stress tolerance of the lifting device etc. The pre-determined distance above the lower end 3 may i.e. be in the range from 0.1 to 0.3 times the length of the length extension device.

(7) It may also be advantageous to prevent the piston 9 is not pushed all the way up to such that it buts against the first end 2 to maintain the heave compensating ability during the Quick lift phase. This may be obtained by adapting the amount of pre-stored gas inside the expansion tank 29 such that when the gas is permitted to flow into the upper chamber 22 of the gas accumulator 16, it forms a gas pressure in chamber 22 which is able to push piston 9 up to a pre-determined distance below the first end 2 of the length extension device 1. The pre-determined distance below end 2 may i.e. be in the range from 0.1 to 0.3 times the length of the length extension device.

(8) The amount of pre-stored gas in the upper chamber 22 and in the expansion tank 29 become thus a function of the sensible weight of the load towards piston 9, such that the weight of the load should be known within an accuracy of i.e. ±10% in order to determine how much gas which needs to be pre-stored in the gas accumulator and in the gas tank. Further, since the gas from the gas tank is to flow into the gas accumulator to push piston 9 towards the upper end 2, the pressure in the pre-stored gas in the expansion tank 29 needs to be higher than the pressure of the pre-stored gas in the upper chamber 22. The amount of pre-stored gas in the expansion tank of the gas tank and in the upper chamber of the gas accumulator depends on the mass of the load, the Response Amplitude Operator (RAO) of the vessel, and the characteristics of the crane.

(9) The initiating of the Quick lift, i.e. when the gas is to be permitted to flow into the gas accumulator, may advantageously “play along with the nature” by having an operator trigging the Quick lifting sequence when the carrying vessel is at a wave crest to ensure the maximum time window for lifting the load before the cargo vessel begins to move towards the load again at the next wave.

(10) If a Quick lift is to be executed, the desired amounts of gas are accumulated in the gas accumulator 16 and in the gas tank 29 of the heave compensator, and it is attached in its upper end 2 to the lifting device 7 and in its lower end (lower end 10 of the piston rod 8) to the load 11 as shown in FIG. 2. All valves on the gas outlets of the heave compensator are closed, and valve 17 of the liquid transferring device is open.

(11) The computer program module “Quick lift” is engaged by an external guidance signal transmitted from the operator via the radio transmitter/receiver of the control unit 110, and contains data instructions which, when executed in the data processing unit of the control unit 110, causes the following process steps to be executed in successive order: 1) Wait for a guidance signal from the operator. 2) Upon receiving of the guidance signal, open valves 24 and 30 to cause gas under high pressure flowing from the expansion tank 29 into the upper chamber 22.

(12) In a second aspect, the data processing unit 104 additionally comprises a Quick lift computer program module, containing data instructions which when executed in the data processing unit, performs a method comprising the following steps in successive order: a) awaiting signal for executing the Quick lift computer program module is received, and then b) open valves 24 and 30.

Example Embodiment 2, Weight Compensation

(13) This functionality is an automatic regulation of the equilibrium position of the piston of the length extension device intended to maintain a maximum stroke length regardless the sensible weight of the load when the load is freely suspended in air.

(14) After the execution of a Quick lift which raises the piston to an upper position in the length extension device, this functionality needs, in most lifting operations, only to lower the equilibrium position of the piston to approximately the middle of the length extension device. This example embodiment will thus describe this case. However, this is not to be interpreted as a limitation. It may also comprise the possibility of lifting the piston if it becomes below the desired equilibrium position, by letting gas flow from the gas tank (if it has sufficient high pressurised gas resources) into the gas accumulator.

(15) The computer program module “Weight compensation” is engaged by an external guidance signal transmitted from the operator via the radio transmitter/receiver of the control unit 110, and contains data instructions which, when executed in the data processing unit of the control unit 110 causes the following process steps to be executed in successive order: 1) Controlling that valve 17 is open and that valves 24, 30, and 33 are closed, and await a guidance signal from the operator. 2) Upon receiving the guidance signal, await a predetermined time and read the signal from sensors 19 and 27 and determine the pressure and temperature in the accumulator and the position of piston 9, and employ these data to calculate the amount (in mass) of gas present in the accumulator at the moment, m.sub.k.sup.acc, and the amount of gas required in the gas accumulator to obtain the desired equilibrium position of the piston, m.sub.sp.sup.acc. 3) Thereafter, open valves 24 and 32 to allow gas being discharged out of the gas accumulator. 4) Reading the pressure and temperature in the accumulator and the position of piston 9 continuously via sensors 19 and 27, and calculate continuously the amount of gas present in the gas accumulator, m.sub.k.sup.acc, and employ this value to calculate Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc. 5) When |Δm.sub.sp|<K, close valves 24 and 32 and stop the execution of the program module.

(16) The calculation of the amount gas present in the gas accumulator is performed by applying the gas equation of state for an ideal gas utilising the registered values of the gas pressure and temperature inside the gas accumulator and by calculating the volume of the upper chamber 22 in the gas accumulator by utilising the registered position of piston 9 to determine its position S.sub.k:

(17) $\begin{array}{cc}{m}_k^{\mathrm{acc}}=\frac{P_k^{\mathrm{acc}}\left(V_{\mathrm{acc}}-A_o{S}_k\right)}{T_k^{\mathrm{acc}}{R}_{N2}}& \left(1\right)\end{array}$

(18) Here m.sub.k.sup.acc is the amount of gas inside the accumulator at time k, p.sub.k.sup.acc is the pressure in the gas at time k, T.sub.k.sup.acc is the temperature of the gas at time k. R.sub.N2 is the gas constant, V.sub.acc is the complete volume of the gas accumulator, and A.sub.0S.sub.k is the volume of the liquid filled chamber 15 at time k. A.sub.0 is the area of the piston 21 of the accumulator. When the control unit 110 calculates the amount of gas required in the gas accumulator at the desired equilibrium position, it employs eqn. (1) with the value S.sub.sp instead of S.sub.k, where S.sub.sp is the desired volume of chamber 15. The stop criterion K is a predetermined constant, which may i.e. be 5% of desired amount of gas.

(19) In a third aspect, the data processing unit 104 additionally comprises a Weight compensating computer program module, containing data instructions which when executed in the data processing unit, performs a method which in addition to the method steps of the second aspect, also comprising the following steps in successive order: d) controlling that valve 17 is open and valves 24, 30, and 33 are closed, and register continuously the signal from the position sensor 19 and pressure and temperature sensor 27, e) awaiting an execution signal from the operator, and when receiving the execution signal, await a predetermined time, and then calculate the equilibrium position of piston 9 from the registered position data from position sensor 19 and employ this value together with the pressure and temperature values from the pressure and temperature sensor 27 in eqn. (1) to calculate the desired amount of gas in the gas accumulator, m.sub.sp.sup.acc, and thereafter calculate continuously the present amount of gas in the gas accumulator, m.sub.k.sup.acc, f) thereafter, open valves 24 and 33, and calculate Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc, and g) when |Δm.sub.sp|<K, where K is a predetermined stop criterion, close valves 24 and 33.

Example Embodiment 3, Lowering Preparation

(20) This functionality ensures a “pre-setting” of the pressure in the gas tank for enabling lowering the dampening characteristics at great water depths by increasing the available volume of the gas phase by allowing the gas to flow freely between the gas tank and gas accumulator. In order to enable free gas flow between the gas tank and gas accumulator, the gas pressure in the gas tank needs to be more or less the same as the gas pressure in the gas accumulator when valves 24 and 30 are opened, otherwise the pressure change in the gas accumulator may cause an unacceptable change of the equilibrium position of the piston of the length extension device. The actual size of the pressure difference that may be tolerated depends on the sensible weight of the load, the stroke length of the length extension device, the water depth when opening valves 24 and 30, and may be up to a few bars. In order to obtain this functionality, it is necessary to calculate/determine in advance which pressure that will be present in the gas accumulator when the valves 24 and 30 are being opened, and then to adjust the pressure of the gas tank to the same value before the heave compensator is lowered to great water depths and discharge of the gas becomes impossible due to the hydrostatic pressure of the water. This calculation may advantageously take into account the amount of gas that is to be transferred from the gas accumulator to the gas tank as a consequence of the steps of regulating the stroke length. The calculation of the desired gas pressure in the expansion tank 29 may be performed by estimating the sensible weight of the load at the intended water depth and then calculating which pressure needs to be obtained in the liquid in chamber 5 to counter the tensile force on piston 9.

(21) This functionality may advantageously be executed shortly after the load has obtained contact and been lowered a short distance into the water masses, but it may also be executed when the load is freely suspended in air, or after it has been lowered a bit longer distance into the water masses. The functionality may i.e. by the control unit 110 reading the signals from a fourth pressure and temperature sensor which measures the pressure of the surroundings of the device initiate the Lowering preparation when the heave compensator has reached e predetermined water depth, such as i.e. 100 m.

(22) In a fourth aspect, the data processing unit 104 additionally comprises a Lowering compensation computer program module, containing data instructions which when executed in the data processing unit, performs a method comprising the following steps in successive order: d0) controlling that valve 17 is open and valves 24, 30, and 33 are closed, d1) continuously reading the signal from the third pressure and temperature sensor 31, d2) determining the desired pressure of the gas phase in the expansion chamber 29 according to a predetermined estimate of the sensible weight of the load at the intended water depth, and calculate the pressure of the liquid in chamber 5 needed to balance the tensile force on piston 9 due to the sensible weight of the load, d3) opening valves 30 and 33, and d4) when the signal from the third pressure and temperature sensor 31 shows that the pressure in the expansion tank 29 has reached the desired pressure, close valve 33.

Example Embodiment 4, Depth Compensation

(23) This functionality has the intention of regulating the equilibrium position of the piston of the length extension device in accordance with increasing hydrostatic pressures around the heave compensator when it is lowered into the water masses. This functionality may typically be triggered for each 50th meter water depth, and may advantageously be fully automatic due to practicalities associated with transmitting readable guidance signals from the surface down into deep water masses. This automechanism may be obtained by continuously feeding the data processing unit of the control unit 110 with pressure and eventual temperature data from the fourth pressure and temperature sensor which registers the temperature and pressure of the surroundings of the heave compensator, and utilising these data to determine when to execute the compensation of the equilibrium position of the piston. The regulation of the equilibrium position is obtained in the same manner as in example embodiment 2, with the exception that the gas being discharged from the gas accumulator is transferred to the gas tank when the hydrostatic pressure of the surrounding water masses makes it difficult/impossible to ventilate the gas out through outlet 32. In practice, this will be the case when the hydrostatic pressure of the water masses has reached about 50% of the gas pressure in the gas accumulator.

(24) In a fifth aspect, the data processing unit 104 additionally comprises a Depth compensation computer program module, containing data instructions which when executed in the data processing unit, performs a method comprising the following steps in successive order: A) controlling that valve 17 is open and valves 24, 30, and 33 are closed, B) continuously registering the signal from the fourth pressure and temperature sensor and utilising the signal to estimate the water depth, C) continuously reading the signal from position sensor 19 and pressure and temperature sensor 27, and D1) when the water depth has increased with a predetermined interval and the pressure of the surrounding water is less than 50% of the gas pressure inside the gas accumulator, execute steps from i) up to and including iii): i) await a predetermined time, and then calculate the equilibrium position of piston 9 from the registered position data from position sensor 19, and employ this value together with the pressure and temperature values from the pressure and temperature sensor 27 in eqn. (1) to calculate the desired amount of gas in the gas accumulator, m.sub.sp.sup.acc, and thereafter calculate continuously the present amount of gas in the gas accumulator, m.sub.k.sup.acc, ii) thereafter, open valves 24 and 33, and calculate continuously Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc, and iii) when |Δm.sub.sp|<K, where K is a predetermined stop criterion, close valves 24 and 33 and return to step A), D2) when the water depth has increased with a predetermined interval and the pressure of the surrounding water is larger than 50% of the gas pressure inside the gas accumulator, execute steps from j) up to and including jjj): j) await a predetermined time, and then calculate the equilibrium position of piston 9 from the registered position data from position sensor 19, and employ this value together with the pressure and temperature values from the pressure and temperature sensor 27 in eqn. (1) to calculate the desired amount of gas in the gas accumulator, m.sub.sp.sup.acc, and thereafter calculate continuously the present amount of gas in the gas accumulator, m.sub.k.sup.acc, jj) thereafter, open valves 24 and 30, and calculate continuously Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc, and jjj) when |Δm.sub.sp|<K, where K is a predetermined stop criterion, close valves 24 and 30 and return to step A).

Example Embodiment 5, Reduction of Spring Resistance

(25) This functionality will usually be employed when a load is to be lowered to great water depths, and is usually triggered by the fourth pressure and temperature sensor of the device sensing that the desired water depth is obtained.

(26) In a sixth aspect, the data processing unit 104 additionally comprises a Reduction of spring resistance computer program module, containing data instructions which when executed in the data processing unit, performs a method comprising the following steps: A1) continuously registering the signal from the fourth pressure and temperature sensor and utilising the signal to estimate the water depth, and A2) when the water depth has reached a predetermined depth, open valves 24 and 30.

Example Embodiment 6, Lock and Release

(27) This functionality may be useful when a load is turned over the side of the cargo vessel and when there is a small distance between the load and vessel that induces a risk of contact. In such cases it may be an advantage to lock the piston of the length extension device to reduce the risk of a heave movement lowering the load downwards against the side of the vessel.

(28) This functionality may advantageously be combined with the Weight compensation functionality, and would normally be operator controlled by the operator sending a radio signal which is received by the radio receiver of the control unit 110, which locks the piston to prevent it from moving inside the length extension device. Release is obtained by the operator sending guidance signal which unlocks the piston. This may easily be obtained by closing and opening, respectively, valve 17 to prevent or allow liquid to flow in or out of chamber 5 of the length extension device.

(29) In a seventh aspect, the data processing unit 104 additionally comprises a Reduction of spring resistance computer program module, which when executed in the data processing unit, performs a method characterised in that in addition to the steps of third aspect, additionally comprises the following step: h) upon receiving a locking signal from the operator, close valve 17, and i) upon receiving a release signal from the operator, open valve 17.

Example Embodiment 7, Landing Compensation

(30) This functionality is in one sense the opposite of the Quick lift functionality in that the pre-stored gas pressure in the gas tank is lower than the pressure in the accumulator, as opposed to higher as in the Quick lift, such that when the Landing compensation is to be executed, it will cause a sudden decrease in the lifting force such the load is standing steady against the ground. This is a useful functionality for cases where a load is to be deployed on a solid ground, such as a quay etc. and there is a risk for heave movements causing the load to be re-lifted off the ground after making first contact and thereafter banging down onto the ground.

(31) In an eight aspect, the data processing unit 104 additionally comprises a Reduction of spring resistance computer program module, containing data instructions which when executed in the data processing unit, performs a method characterised in that in addition to the steps of third aspect, additionally comprises the following steps in successive order: h) upon receiving a signal from an operator to initiate the Landing compensation, determine the desired pressure, p.sub.sp.sup.exp, of the gas phase in the expansion chamber 29 by reading the actual pressure, p.sub.k.sup.acc, in the gas accumulator registered by the pressure and temperature sensor 27, and set p.sub.sp.sup.exp=ƒ.Math.p.sub.k.sup.acc, where ƒε<0, 1>, i) continuously reading the signal from the third pressure and temperature sensor 31, j) controlling that valve 24 is closed and thereafter open valves 30 and 33, and close valve 33 when the desired pressure, p.sub.sp.sup.exp, of the gas phase is obtained, and k) upon receiving a signal from the operator to execute the Landing compensation, open valve 24.

(32) The determination of the desired pressure, p.sub.sp.sup.exp, in the gas chamber may be obtained by setting it to a factor F, which is between 0 and 1 times the pressure, p.sub.k.sup.acc in chamber 22 of the gas accumulator at the initial phase of the function, preferably a factor between 0.5 and 0.95 times p.sub.k.sup.acc, between 0.6 and 0.9 times p.sub.k.sup.acc, or between 0.7 and 0.8 times p.sub.k.sup.acc.

(33) Alternatively, in cases where a faster Landing compensation is desired, it may be based on use of valve 17 on the liquid transferring device instead of the gas valves 24, 30. In this case, the heave compensator is being pre-stored with sufficient amount of gas before initiating the lifting operation in the expansion chamber 29 to be able to push the piston 9 towards the first end of the length extension device in the same and analogous manner as the pre-storing of gas for the Quick lift functionality described above. By execution of the rapid landing compensation, the heave compensator is firstly prepared by allowing the gas to flow into the gas accumulator to push piston 9 towards the first end 2 of the length extension device and then locking it in this position by closing valve 17. Thereafter, valve 30 is closed and valves 24 and 33 opened to discharge gas from the gas accumulator until it contains sufficient amount of gas to be maintain a stable equilibrium position when the piston is lowered towards the second end 3 of the length extension device in the same and analogous manner as the Quick lift functionality. When the desired amount of gas in the upper chamber 22 is obtained, valves 24 and 33 are closed. Preparation to rapid landing compensation may advantageously be controlled by the operator sending a radio signal which is received by the radio receiver of the control unit 10 and triggers this function.

(34) When the heave compensator has executed the preparation for the rapid landing compensation, the piston 9 will be locked in a relatively close distance from the first end of the length extension device, and the amount of gas in the upper chamber 22 is reduced to a level which is able to form a stable equilibrium position when the piston is lowered to a relatively short distance above the second end 3 of the length extension device. Then the actual rapid landing compensation may be obtained by only opening valve 17 to allow liquid to flow out of the length extension device and thus almost immediately reduce the tension forces on the load, the heave compensating device and the lifting device to a level ensuring that heave movements are unable to re-lifting the load from the ground it is to be deployed, and in the next moment banging down again on the ground and be damaged.

(35) In a ninth aspect, the data processing unit 104 additionally comprises a rapid landing compensation computer program module, containing data instructions which when executed in the data processing unit, causes the following process steps to be executed in successive order: awaiting receiving signal to preparation of rapid landing compensation from the operator, upon receiving a signal from an operator to execute preparation of rapid landing compensation, open valves 24 and 30 such that gas under high pressure flows from the expansion chamber 29 of the gas tank and into the upper chamber 22, and piston 9 is pushed towards the first end 2, after a predetermined time period, close valves 17 and 30, regulate thereafter the pressure in the gas accumulator to the desired by continuously registering the signal from the position sensor 19 and pressure and temperature sensor 27, and use the registered position data from sensor 19 to calculate the equilibrium position of piston 9, and utilise this value together with the pressure and temperature values from pressure and temperature sensor 27 in eqn. (1) to calculate the desired amount of gas, m.sub.sp.sup.acc, and thereafter continuously calculating the present amount of gas inside the gas accumulator, m.sub.k.sup.acc, opening thereafter valve 33 and calculate continuously Δm.sub.sp=m.sub.k.sup.acc−m.sub.sp.sup.acc, and when |Δm.sub.sp|<K, where K is a predetermined stop criterion, close valve 33, awaiting receiving signal to executing the rapid landing compensation from the operator, upon receiving the signal from the operator to execute the rapid landing compensation, open valve 24.

(36) The sufficient amount gas in the expansion tank of the gas tank depends on the mass of the load, the Response Amplitude Operator (RAO) of the vessel, and the characteristics of the crane. The term “sufficient amount of gas” is in this context to be understood as the gas tank need to have sufficient amount of gas under high pressure to be able to at least be able to push the piston of the length extension device up to the first end of the length extension device when the pressure between the expansion tank 29 and the upper chamber 22 is equalised by allowing the gas to flow freely between the expansion chamber 29 and the upper chamber 22. Sufficient amount of gas needs to be determined for each lifting operation, but is a task within the ordinary skills of a person skilled in the art.

(37) In all seven example embodiments, all regulations of liquid and/or gas flows in the heave compensator are described as opening or closing one or more of the first 17, second 24, third 30, and fourth 33 valve. It may however, also be applied a bypass conduit with a reduced through-flow capacity across one or more of these valves, and which may be opened or closed by a pressure compensating valve (not shown in the Figure). In such cases, the fluid flow (i.e. gas in the first 23, second 25, and/or third 32 gas outlet, and liquid in the first 13 liquid outlet) may be regulated by only opening/closing the respective pressure compensating valve, only opening the respective valve, or by a combined opening/closing of both the respective valves and pressure compensating valves. The pressure compensating valves have their own activation means which are activated by guidance signals sent by the signal transmitting unit of the control unit 110.