Crane load stabilization using a tugger line

Abstract

Tugger line system (3) for stabilization of a load suspended in an offshore crane system, comprising: a tugger line (5) to be engaged with the load (L); a winch (6) fixed or fixable in the offshore crane system (4) and configured to reel the tugger line in or out from the winch so as to vary a working length of the tugger line; and a damper assembly (8) engaged or engageable with the tugger line between the winch and the load, wherein the damper assembly, when engaged, is configured to passively attenuate fluctuations of tension in the tugger line, said fluctuations being induced by movement of the load with respect to the winch.

Description

[0001] P 137407PC00

[0002] Title: Crane load stabilization using a tugger line

[0003] FIELD

[0004] The invention relates to a tugger line system for stabilization of a load suspended in an offshore crane system, as well as to: a combination of the tugger line system and the offshore crane system; an offshore vessel or structure comprising the combination; uses; a method of stabilizing a load suspended in an offshore crane system; a damper assembly for the tugger line system; and a method of providing the tugger line system.

[0005] BACKGROUND

[0006] Offshore installation of offshore wind turbines can be challenging, in particular due to size and weight of the monopile and / or other components, sea and weather conditions, and a desire for cost efficiency. A particular challenge concerns stabilization of the monopile suspended in an offshore crane system, e.g. on a vessel at a desired offshore installation location. Similar considerations apply to other types of loads in offshore crane systems. More stable loads are easier and safer to handle and put less strain on the crane system. At the same time, it is generally desired to move loads to their desired positions relatively quickly and to limit weight and complexity of the crane system.

[0007] For load stabilization during crane operations, it is known to use tugger lines engaged with the load, wherein a winch can be controlled to reel the tugger line in or out from the winch so as to vary a working length of the tugger line. Essentially, a maximum distance between the winch and the load can be imposed in this way. However, it has been found that loads may still sway in response to disturbances. In view thereof, further improvement is desired. SUMMARY

[0008] An object is to improve load stability during offshore crane operations. An object is to facilitate relatively effective and efficient installation of offshore wind turbines.

[0009] An aspect provides a tugger line system for stabilization of a load suspended in an offshore crane system. The tugger line system comprises: a tugger line to be engaged with the load; and a winch fixed or fixable in the offshore crane system, in particular to a load bearing part thereof, and configured to reel the tugger line in or out from the winch so as to vary a working length of the tugger line. The tugger line system comprises a damper assembly engaged or engageable with the tugger line between the winch and the load, wherein the damper assembly, when engaged, is configured to passively attenuate fluctuations of tension in the tugger line. Said fluctuations are in particular induced by movement of the load with respect to the winch.

[0010] Advantageously, such a damper assembly can reduce swinging of the load, in particular in combination with the functionality of the winch. Surprisingly, while the passive attenuation of tension fluctuation may be considered to somewhat attenuate the traditional position control from the winch, it has been found that overall load stability tends to improve.

[0011] In this respect, it is considered that in a known tugger line system without the damper assembly, the load may swing towards the winch by some transient disturbance, after which the load may swing back away from the winch until reaching a maximum distance imposed by the winch. At that time, the load may stop and reverse, resulting in cyclic or oscillatory swinging and thus ongoing load instability. By contrast, by passively attenuating fluctuations of tension using the damper assembly, peak tensions can effectively be reduced, and thereby the oscillatory swinging can be reduced. It is considered that the damper assembly can dissipate energy from such swinging motions, thereby promoting stability. Meanwhile, the traditional functionality of the combination of the tugger line and the winch can essentially be maintained. In other words, the addition of the damper assembly need not interfere with the normal operation of the tugger line. As the damper assembly is configured to perform the attenuation passively, control of the tugger line need not be complicated by the addition of the damper assembly.

[0012] In the present context, the passive attenuation of fluctuations of tension in the tugger line can be regarded as a form of passive damping, i.e. damping that does not require active control or an external power source. Nevertheless, it shall be appreciated that in some embodiments an external power source or active control may be associated with the damper assembly. For example, the damper assembly may be configured to be activated or deactivated or otherwise adjusted using active control, or an external power source may be used to prepare the damper assembly for use. During use, energy for the passive attenuation is essentially extracted from the process to be attenuated, e.g. in the present case swinging of the load. In contrast, active attenuation or damping involves active control and an external power source, wherein for example in response to a sensed disturbance a controller is configured to activate generation of a counter force using an external power source. In other words, active attenuation or damping involves an externally powered attenuation or damping action taken in response to a detection indicating a swinging of the load, while passive attenuation or damping inherently opposes such swinging.

[0013] Optionally, the damper assembly, when engaged, is configured to bias the tension in the tugger line to below a predefined tension threshold.

[0014] In this way, the passive attenuation can be particularly effectively configured to promote load stabilization. In this respect, it is noted that some level of tension is generally desired during use of a tugger line, whereas excessive tension tends to be associated with erratic motions. For example, when the load swings away from the winch, tension in the tugger line may peak when the load reaches an imposed maximum distance from the winch. At that time, the high tension tends to pull the load back towards the winch, thereby continuing the undesired swinging. When the tension is biased to below the predefined tension threshold, i.e. away from said threshold towards lower tension, such continued swinging can be suppressed.

[0015] Optionally, the damper assembly, when engaged, is configured to reduce, in particular passively, an effective reeving length for the tugger line when the tension in the tugger line exceeds a predefined tension threshold, e.g. the predefined tension threshold mentioned above.

[0016] By reducing the effective reeving length, i.e. the length of the portion of the line that is held in the reeving, the tension in the tugger line can effectively be limited or reduced, in particular in case of the load swinging away from the winch. Essentially, the reduction in effective reeving length can provide some increase of the working length of the tugger line, so that a lower tension can be obtained for a same pulling force from the load, or a same tension can be maintained for an increased pulling force from the load, etc.

[0017] Optionally, the damper assembly, when engaged, is additionally configured to increase, in particular passively, the effective reeving length for the tugger line when the tension in the tugger line is below a predefined tension threshold. The predefined tension threshold for increasing the reeving length is preferably the same as or lower than the predefined tension threshold for reducing the reeving length. In this way, overall attenuation of tension fluctuations can be enhanced, wherein for example a desired minimum tension can be maintained.

[0018] Optionally, the damper assembly is configured to attenuate the fluctuations using a passively operated hydraulic or pneumatic circuit of the damper assembly. Optionally, the damper assembly is a hydraulic or pneumatic damper assembly. Advantageously, a hydraulic or pneumatic circuit can facilitate well-regulated passive attenuation, in particular in a relatively efficient and robust manner. A hydraulic circuit may be particularly preferred in case of relatively large loads, whereas a pneumatic circuit may be preferred in some situations where use of hydraulic fluid is un desired.

[0019] Optionally, the damper assembly comprises a piston-cylinder assembly comprising a cylinder and a piston movable in the cylinder along a cylinder axis of the cylinder.

[0020] Such a piston-cylinder assembly can provide an effective interface between the tugger line and a hydraulic or pneumatic circuit for the passive attenuation. For example, as explained further elsewhere herein, the pistoncylinder assembly may be coupled to a reeving for the tugger line, such that relative movement of the piston and the cylinder varies an effective reeving length for the tugger line.

[0021] Optionally, one of the piston and the cylinder is engaged or engageable with the tugger line, wherein preferably the other of the piston and the cylinder is fixed or fixable in the offshore crane system, in particular to a, e.g. the, load bearing part thereof.

[0022] By the engagement with the tugger line, forces can be exchanged between the piston-cylinder assembly and the tugger line. By the fixation to the load bearing part, the load bearing part can provide an effective counter force, and more generally the piston-cylinder assembly can be stably positioned. For example, the piston-cylinder assembly may be fixed to a same load bearing part as the winch, and may thus be positioned close to the winch. Nevertheless, it shall be appreciated that the winch and the damper assembly need not necessarily be close to each other, in particular because the passive attenuation can in principle be performed anywhere along the tugger line between the winch and the load.

[0023] Optionally, the damper assembly is arranged to change an effective reeving length for the tugger line by movement of the piston with respect to the cylinder along the cylinder axis, in particular in passive response to a change in the tension in the tugger line.

[0024] As alluded to above, by thus coupling the piston-cylinder assembly to a reeving for the tugger line, an effective interface between the tugger line and the hydraulic or pneumatic circuit can be realized for the passive attenuation. Using the reeving, a tension in the tugger line may be exerted as an axial force on the piston-cylinder assembly, urging relative movement of the piston and the cylinder, which relative movement in turn can change the effective reeving length for the tugger line at the damper assembly. In this way, depending on the configuration of the hydraulic or pneumatic circuit, an increase in tension in the tugger line can be passively converted to a reduction in effective reeving length and thus an increase in working length of the tugger line, in turn resulting in limitation or reduction of the tension.

[0025] Optionally, an end of the cylinder where the piston can move towards to reduce the effective reeving length is defined as a high-pressure end, wherein an opposite end of the cylinder where the piston can move towards to increase the effective reeving length is defined as a low-pressure end.

[0026] In this way, as explained further below, the piston-cylinder assembly can be effectively configured as part of the hydraulic or pneumatic circuit to provide the desired passive attenuation functionality.

[0027] Optionally, the damper assembly comprises a relief valve arranged to drain hydraulic or pneumatic fluid from the high-pressure end of the cylinder as pressure of said fluid exceeds a predefined pressure threshold, in particular while otherwise blocking said draining.

[0028] In this way, the above described functionality regarding the predefined tension threshold can be realized particularly effectively using the hydraulic or pneumatic circuit. For example, the relief valve may remain closed as long as the tension in the tugger line is below the predefined tension threshold, allowing the tension in the tugger line and thus the fluid pressure at the high-pressure end of the cylinder to increase up to said threshold. Then, upon a further increase, the relief valve opens, e.g. proportionally to the excessive pressure, thereby suppressing the further increase of pressure and allowing the piston to move further towards the high-pressure end of the cylinder so as to reduce the effective reeving length of the tugger line. Thus, as part of the hydraulic or pneumatic circuit that is coupled to the tugger line using the piston-cylinder assembly, the relief valve can essentially facilitate that the effective reeving length of the tugger line is reduced in passive response to excessive tension in the tugger line, in particular while otherwise inhibiting such a reduction in effective reeving length.

[0029] Optionally, the damper assembly comprises a one-way valve arranged in parallel to the relief valve to allow hydraulic or pneumatic fluid to flow into the cylinder at the high-pressure end, in particular while preventing draining of hydraulic or pneumatic fluid from the high-pressure end otherwise than via the relief valve.

[0030] Such a one-way valve advantageously allows refilling of the cylinder with hydraulic or pneumatic fluid at the high-pressure end to allow the piston-cylinder assembly to return to a neutral state after the piston has been moved towards the high-pressure end. As a possible alternative to the one-way valve, the relief valve may be adjustable, e.g. electromechanically, to selectively allow such refilling of the cylinder. It shall be appreciated that in such a case, despite a possible active adjustment of the relief valve, the attenuation of the tension fluctuations is still passive. In particular, the adjustment of the relief valve does not actively drive the cylinder with respect to the piston.

[0031] Optionally, the damper assembly is configured to allow hydraulic or pneumatic fluid to flow into and out from the low-pressure end of the cylinder, in particular substantially without requiring any minimum pressure of said fluid.

[0032] In this way, pressure at the low-pressure end can be substantially unaffected by displacement of the piston with respect to the cylinder. Specifically, such displacements can be accompanied by corresponding changes in filling of the cylinder at the low-pressure end. This allows the movement of the piston with respect to cylinder in response to changes in tension in the tugger line to be dominated by the pressure at the high pressure end.

[0033] Optionally, the damper assembly comprises an accumulator arranged to store hydraulic or pneumatic fluid therein, in particular for exchange thereof with the cylinder.

[0034] Such an accumulator can enable the cylinder to remain filled and appropriately pressurized, in particular without requiring active components such as a pump.

[0035] A further aspect provides a combination of one or more tugger line systems as described herein and the offshore crane system. Optionally, for at least one of the one or more tugger line systems, the winch is fixed in the offshore crane system, in particular to the load bearing part. Optionally, for at least one of the one or more tugger line systems, the damper assembly is engaged with the tugger line. Optionally, for at least one of the one or more tugger line systems, the tugger line is engaged with the load.

[0036] Advantages of such a combination correspond to those described above for the tugger line system.

[0037] Optionally, for at least one of the one or more tugger line systems, the load bearing part is, or is part of, a gantry trolley of a gantry crane of the offshore crane system. Optionally, for at least one of the one or more tugger line systems, the load bearing part is, or is part of, a crane boom of the offshore crane system. Optionally, for at least one of the one or more tugger line systems, the load bearing part is, or is part of, a crane pedestal of the offshore crane system. Optionally, for at least one of the one or more tugger line systems, the load bearing part is, or is part of, a part of an offshore structure, such as a vessel or a platform, on which a movable part of the offshore crane system is supported. Optionally, the load is, comprises, or is part of, a monopile or other component for an offshore wind turbine or a foundation therefor. Optionally, the load is, comprises, or is part of, a hammer tool for hammering a monopile for an offshore wind turbine into a seabed. Optionally, the combination is configured for the tugger line of at least one of the one or more tugger line systems to be engaged with the load via at least one of: a crane block of the offshore crane system; a monopile upending tool, in particular a flange monopile upending tool; a line connector attached to, or formed as part of, the load.

[0038] Thus, the improved tugger line system can be used in a highly versatile manner in the context of offshore crane operations. Essentially, the passive attenuation can be applied for any tugger line.

[0039] A further aspect provides an offshore vessel or structure comprising a combination as described herein of the one or more tugger line systems and the offshore crane system.

[0040] Advantages of such a vessel or structure correspond to those described above with respect to the tugger line system and the offshore crane system. The offshore crane system may comprise part or all of the vessel or structure, wherein in particular one or more fixed parts of the vessel or structure may support one or more movable parts of the offshore crane system. Thus, in some cases, the vessel or structure may essentially form and / or be the offshore crane system, and vice versa.

[0041] Optionally, the offshore vessel is configured for installation of a monopile for an offshore wind turbine at an offshore installation location, and preferably configured for transport of said monopile to said offshore installation location. It has been found that the passive attenuation for the tugger lines can be particularly beneficial for crane operations on such vessels.

[0042] A further aspect provides a use of a tugger line system as described herein for stabilization of a load suspended in an offshore crane system.

[0043] A further aspect provides a use of a combination as described herein of the one or more tugger line systems and the offshore crane system for offshore crane operations, in particular for installation of a monopile for an offshore wind turbine at an offshore installation location.

[0044] A further aspect provides a method of stabilizing a load suspended in an offshore crane system, comprising: engaging a tugger line with the load; using a winch, setting a working length of the tugger line in accordance with a desired position of the load; and passively attenuating fluctuations of tension in the tugger line using a damper assembly engaged with the tugger line between the winch and the load. Said fluctuations are in particular induced by movement of the load with respect to the winch. Optionally, the tugger line, winch and damper assembly are those of a tugger line system as described herein.

[0045] Optionally, the passive attenuation comprises at least one of: biasing the tension in the tugger line to below a predefined tension threshold; reducing an effective reeving length for the tugger line when the tension in the tugger line exceeds a, e.g. the, predefined tension threshold; passively operating a hydraulic or pneumatic circuit comprising a pistoncylinder assembly; using a, e.g. the, piston-cylinder assembly, reducing an effective reeving length for the tugger line in passive response to an increase of the tension in the tugger line; using a relief valve, in particular in the hydraulic or pneumatic circuit, limiting an increase of the tension in the tugger line to a, e.g. the, predefined tension threshold.

[0046] Advantages of such further aspects correspond to those described above for other aspects. A further aspect provides a damper assembly evidently configured as the damper assembly of a tugger line system as described herein.

[0047] A further aspect provides a method of providing a tugger line system according as described herein, comprising: providing an initial tugger line system for stabilization of a load suspended in an offshore crane system, the initial tugger line system comprising: the tugger line to be engaged with the load, and the winch fixed or fixable in the offshore crane system and configured to reel the tugger line in or out from the winch so as to vary a working length of the tugger line; and retrofitting a damper assembly as described herein in the initial tugger line system so as to be engaged or engageable with the tugger line between the winch and the load.

[0048] Optionally, the initial tugger line system is part of an offshore crane system of an offshore vessel or platform, in particular for installation of monopiles for offshore wind turbines.

[0049] Thus, a damper assembly as described herein may be added to an existing tugger line system, enabling reuse of the existing system while also providing the additional benefits of the passive attenuation.

[0050] It shall be appreciated that aspects and options described herein may be variously combined. So, for example, options described for a system may be correspondingly applied to a related method, and vice versa.

[0051] DETAILED DESCRIPTION

[0052] In the following, the invention will be explained further using examples of embodiments and drawings. The drawings are schematic and merely show examples. In the drawings, corresponding elements are provided with corresponding reference signs. In the drawings:

[0053] Fig. 1 shows a wireframe perspective view of an offshore vessel with an offshore crane system, wherein a monopile is suspended as load in the crane system; Fig. 2 shows a wireframe perspective view of an offshore vessel with an offshore crane system, wherein a hammer tool is suspended as load in the crane system;

[0054] Fig. 3 shows a side view of a tugger line system comprising a damper assembly;

[0055] Fig. 4 shows a diagram of a damper assembly in a neutral state;

[0056] Fig. 5 shows a diagram of the damper assembly in an attenuating or damping state;

[0057] Fig. 6 shows a diagram of the damper assembly in a recovering state;

[0058] Fig. 7 shows a side view of a combination of two tugger line systems each comprising a respective damper assembly; and

[0059] Fig. 8 shows a top view of a further combination of two tugger line systems each comprising a respective damper assembly.

[0060] Figs. 1 and 2 show examples of an offshore vessel 1 in different stages of use. The shown vessel 1 is configured for installation of a monopile 2 for an offshore wind turbine at an offshore installation location, and configured for transport of said monopile 2 to said offshore installation location. In Fig. 1, a monopile 2 is suspended as load L, using both a main crane 17 and a gantry crane 12. In Fig. 2, a hammer tool 16 is suspended as load L, using the main crane 17.

[0061] The shown offshore vessel 1 comprises an offshore crane system 4 and a combination of several tugger line systems 3 for stabilization of a load L suspended in the offshore crane system 4. It shall be appreciated that various types and configurations of offshore crane and offshore vessel system are possible. Alternatively or additionally to an offshore vessel 1, such a combination may be comprised by an offshore structure such as an offshore platform, for example. Such a combination may be used for offshore crane operations, in particular for installation of a monopile 2 for an offshore wind turbine at an offshore installation location.

[0062] Fig. 3 shows an example of such a tugger line system 3. The tugger line system 3 comprises: a tugger line 5 to be engaged with the load L; a winch 6 fixed or fixable in the offshore crane system 4, in particular to a load bearing part 7 of the offshore crane system 4, and configured to reel the tugger line 5 in or out from the winch 6 so as to vary a working length W of the tugger line 5; and a damper assembly 8 engaged or engageable with the tugger line 5 between the winch 6 and the load L. The damper assembly 8, when engaged, is configured to passively attenuate fluctuations of tension in the tugger line 5. Said fluctuations are induced by movement of the load L with respect to the winch 6. The hydraulic or pneumatic circuit 19 shown in different states in Figs. 4-6 is part of the damper assembly 8 shown in Fig. 3, even though Fig. 3 shows the piston-cylinder assembly 20 without the other parts of the circuit 19.

[0063] Preferably, in particular when the combination of the crane system 4 and the tugger line system 3 is in use, the winch 6 is fixed to the load bearing part 7, the damper assembly 8 is engaged with the tugger line 5, and the tugger line 5 is engaged with the load L.

[0064] Figs. 7 and 8 each show an example of how multiple such tugger line systems 3 can be used for a same load L, as can also be seen in Figs. 1 and 2. In the example of Fig. 7, the load L is suspended from a hoist line 9 via a crane block 10. Here, one of the tugger line systems 3 is engaged with the load L via the crane block 10 while the other tugger line system 3 is engaged with the load L more directly. In the example of Fig. 7, the respective tugger lines 5 approach the load L from substantially opposite directions. In the example of Fig. 8, the respective tugger lines 5 approach the load L from substantially similar directions. It shall be appreciated that various configurations of crane systems, tugger line systems and tugger lines are possible, including those where more than two tugger lines are used for a same load, those where one or more tugger lines extend nonhorizontally, and those where tugger lines cross each other e.g. when viewed from above.

[0065] With particular reference to Figs. 1 and 2 as illustrative examples, the load bearing part 7 may be, or may be part of: a gantry trolley 11 of a gantry crane 12 of the offshore crane system 4; a crane boom 13 of the offshore crane system 4; a crane pedestal 14 of the offshore crane system 4; or a part of an offshore structure, such as a vessel 1 or a platform, on which a movable part of the offshore crane system 4 is supported. As examples, the load L may be, may comprise, or may be part of: a monopile 2 or other component for an offshore wind turbine or a foundation therefor; or a hammer tool 16 for hammering a monopile 2 for an offshore wind turbine into a seabed. It shall be appreciated that various other types of load bearing parts and loads are also possible.

[0066] As alluded to above, a tugger line 5 may be engaged with the load L directly or indirectly. For example, the tugger line 5 may be engaged with the load L via: a crane block 10 of the offshore crane system 4; a monopile upending tool, in particular a flange monopile upending tool 18; or a line connector 28 attached to, or formed as part of, the load L.

[0067] The tugger line system 5 may be realized in various ways. In some scenarios, a method of providing the tugger line system 5 may comprise: providing an initial tugger line system for stabilization of a load suspended in an offshore crane system 4, the initial tugger line system comprising: the tugger line 5 to be engaged with the load L, and the winch 6 fixed or fixable in the offshore crane system 4 and configured to reel the tugger line 5 in or out from the winch 6 so as to vary a working length W of the tugger line 5; and retrofitting the damper assembly 8 in the initial tugger line system so as to be engaged or engageable with the tugger line 5 between the winch 6 and the load L. The damper assembly 8 may thus initially be provided separately, for example for retrofitting or replacement purposes, or more generally as a component for eventual use as part of the tugger line system 3.

[0068] Similar to what is described herein regarding the tugger line system 3 comprising the damper assembly 8, the initial tugger line system may be part of an offshore crane system of an offshore vessel or platform, in particular for installation of monopiles 2 for offshore wind turbines.

[0069] As explained further elsewhere herein, the tugger line system 3 may be used for stabilization of the load L suspended in the offshore crane system 4. Such stabilization may be desired in case of a disturbance force D acting on the load, in particular when the direction of the disturbance force D includes an angle with a hoist line 9 by which the load L may be suspended. Such a disturbance force D can have various magnitudes and directions, can act on the load L directly or indirectly, and can result from various sources, e.g. from wind acting on the load L, rolling or pitching of the vessel 1, or mechanical actions in or on the load L. As explained in the summary section, in the absence of proper attenuation or damping, such disturbances tend to result in undesired swinging of the load.

[0070] The figures also illustrate a method of stabilizing a load L suspended in an offshore crane system 4, comprising: engaging a tugger line 5 with the load L; using a winch 6, setting a working length W of the tugger line 5 in accordance with a desired position of the load L; and passively attenuating fluctuations of tension in the tugger line 5 using a damper assembly 8 engaged with the tugger line 5 between the winch 6 and the load L. Said fluctuations are induced by movement of the load L with respect to the winch 6. The tugger line 5, winch 6 and damper assembly 8 are preferably those of a tugger line system 3 as described herein.

[0071] In the shown examples, the damper assembly 8, when engaged, is configured to bias the tension in the tugger line 5 to below a predefined tension threshold. The method of stabilizing may comprise biasing the tension in the tugger line 5 to below a predefined tension threshold.

[0072] In the shown examples, the damper assembly 8, when engaged, is configured to reduce an effective reeving length R for the tugger line 5 when the tension in the tugger line 5 exceeds a, e.g. the, predefined tension threshold. The method of stabilizing may comprise reducing an effective reeving length R for the tugger line 5 when the tension in the tugger line 5 exceeds a, e.g. the, predefined tension threshold. Thereto, the damper assembly 8 may provide and / or be coupled to a reeving for the tugger line 5, wherein the effective reeving length R can be understood as a variable length of the tugger line 5 present in the reeving. In Fig. 3 it can be seen as example that three sheaves 29 provide such a reeving, wherein distances between the sheaves 29 depend on relative positioning of the piston 22 and cylinder 21, as explained further elsewhere herein.

[0073] In the shown examples, the damper assembly 8 is configured to perform the passive attenuation using a passively operated hydraulic or pneumatic circuit 19 of the damper assembly. In the shown examples, the damper assembly 8 is a hydraulic or pneumatic damper assembly.

[0074] In the shown examples, the damper assembly 8 comprises a pistoncylinder assembly 20 comprising a cylinder 21 and a piston 22 movable in the cylinder 21 along a cylinder axis C of the cylinder 21. In the shown examples, one of the piston 22 and the cylinder 21 is engaged or engageable with the tugger line 5, wherein preferably the other of the piston 22 and the cylinder 21 is fixed or fixable in the offshore crane system 4, in particular to a, e.g. the, load bearing part 7 thereof. In the shown examples, the damper assembly 8 is arranged to change an effective reeving length R for the tugger line 5 by movement of the piston 22 with respect to the cylinder 21 along the cylinder axis C, in particular in passive response to a change in the tension in the tugger line. The method of stabilizing may comprise passively operating a hydraulic or pneumatic circuit 19 comprising a piston- cylinder assembly 20. The method of stabilizing may comprise, using a, e.g. the, piston-cylinder assembly 20, reducing an effective reeving length R for the tugger line 5 in passive response to an increase of the tension in the tugger line 5.

[0075] In the shown examples, an end 23 of the cylinder 21 where the piston 22 can move towards to reduce the effective reeving length R is defined as a high-pressure end 23, wherein an opposite end 24 of the cylinder 21 where the piston 22 can move towards to increase the effective reeving length R is defined as a low-pressure end 24. In the shown examples, the damper assembly 8 comprises a relief valve 25 arranged to drain hydraulic or pneumatic fluid from the high-pressure end 23 of the cylinder 21 as pressure of said fluid exceeds a predefined pressure threshold, in particular while otherwise blocking said draining. The method of stabilizing may comprise, using a relief valve 25, in particular in the hydraulic or pneumatic circuit 19, limiting an increase of the tension in the tugger line 5 to a, e.g. the, predefined tension threshold. A suitable value for such a predefined pressure threshold may be determined using a modelbased calculation and / or routine experimentation, in particular in dependence of relevant factors such as a desired level of attenuation and / or an allowable line pull on the load.

[0076] In the shown examples, the damper assembly 8 comprises a oneway valve 26 arranged in parallel to the relief valve 25 to allow hydraulic or pneumatic fluid to flow into the cylinder 21 at the high-pressure end 23, in particular while preventing draining of hydraulic or pneumatic fluid from the high-pressure end 23 otherwise than via the relief valve 25. As a possible alternative to the one-way valve 26, the relief valve 25 may be adjustable, e.g. electromechanically, to selectively allow hydraulic or pneumatic fluid to flow into the cylinder 21 at the high-pressure end 23.

[0077] In the shown examples, the damper assembly 8 is configured to allow hydraulic or pneumatic fluid to flow into and out from the low- pressure end 24 of the cylinder 21, in particular substantially without requiring any minimum pressure of said fluid.

[0078] In the shown examples, the damper assembly 8 comprises an accumulator 27 arranged to store hydraulic or pneumatic fluid therein, in particular for exchange thereof with the cylinder 21. A fluidic connection between the accumulator 27 and the low-pressure end 24 of the cylinder is preferably valveless and preferably has a low fluidic resistance so as to allow flow between the accumulator 27 and the low-pressure end 24 substantially without requiring any minimum pressure as mentioned above.

[0079] Operation of the damper assembly 8 including the hydraulic or pneumatic circuit 19 may be particularly well understood with reference to Figs. 4-6 illustrating the circuit 19 in different states, as explained further below. Meanwhile, Fig. 3 coupling between the piston-cylinder assembly 20 and the tugger line 5 can be understood from Fig. 3, wherein in particular the effective reeving length R can be understood to be dependent on the relative position of the piston 22 and the cylinder 21, and the tension T in the tugger line 5 can be understood to act on the piston 22.

[0080] In Fig. 4, the circuit 19 is shown in a neutral state, wherein a nonzero but not excessive tension T in the tugger line 5 acts on the piston 22 so as to urge the piston 22 towards the high-pressure end 23 of the cylinder 21. This is counteracted by a static fluid pressure in the cylinder 21 at the high- pressure end 23. At the low-pressure end 24, the cylinder 21 is at a lower static fluid pressure. Here, the piston 22, and indeed the damper assembly 8 overall, is essentially at an equilibrium. It is considered that this is essentially due to a combination of the tension T acting on the piston 22, the action of the relief valve 25, and a difference in surface area between the sides of piston 22 facing the high-pressure end 23 and the low-pressure end 24 of the cylinder 21. Additionally, gravity acting on the piston 22 may contribute to the equilibrium. In Fig. 5, the tension T has increased, for example due to a disturbance D. As a result, the damper assembly 8 is brought out of the equilibrium. Specifically, the tension T leads to increased fluid pressure at the high-pressure end 23. Upon reaching a predetermined pressure threshold, the relief valve 25 responds by allowing fluid to drain from the high-pressure end 23 towards the accumulator 27, which in turn allows the piston 22 to move towards the high-pressure end 23, thereby reducing the effective reeving length R. The reduction in the effective reeving length R tends to suppress the increase in tension T, thus attenuating, in particular damping out, peaks in the tension T. As the piston 22 moves towards the high-pressure end 23, additional fluid can flow into the cylinder 21 at the low-pressure end 24 from the accumulator 27.

[0081] In Fig. 6, the tension T has decreased again, for example to about the same level as in Fig. 4. This can be the result of the attenuation, or of the disturbance D subsiding, or both. At this time, the piston 22 may be returned towards its initial position under fluid pressure from the high- pressure end 23. Specifically, once such pressure decreases below the threshold, the relief valve 25 will close, leaving the fluid between the piston 22 and the high-pressure end 23 essentially trapped there at a pressure that is not excessive but still higher than in the neutral state of Fig. 4. Eventually, using the non-return valve 26 and the pressure present in the accumulator 27, the neutral state of Fig. 4 can be reached again. Thus, the effective reeving length R is then increased again compared to the state of Fig. 5 so as to promote that a minimum tension is maintained in the tugger line 5, in particular in combination with operation of the winch 6.

[0082] In view of the above, it shall be appreciated that such operation of the damper assembly 8, in particular the hydraulic or pneumatic circuit 19, can be performed passively, wherein essentially all energy for the attenuation is extracted from the peaks in tension in the tugger line 5. Over time, the hydraulic or pneumatic fluid may be heated by friction as it flows through the circuit 19, in particular at the relief valve 25. Such heat may be dissipated to the environment of the damper assembly 8 passively.

[0083] Alternatively or additionally, an active cooling arrangement may be provided. It shall be appreciated that, even if the hydraulic or pneumatic fluid is actively cooled, the attenuation by the damper assembly 8 can still be passive attenuation, in particular because such a cooling function is merely auxiliary to the attenuation and not part of the actual attenuation itself.

[0084] Advantageously, while the damper assembly 8 provides the passive attenuation, the winch 6 may be used, in particular controlled, to inhibit the piston 22 from reaching the end of its stroke with respect to the cylinder 21. In particular, the winch 6 may be adjusted to increase or decrease the working length W of the tugger line 5 so as to promote that the tension T is maintained within a range at which the piston 22 is neither in contact with the high-pressure end 23 nor in contact with the low-pressure end 24 of the cylinder 21.

[0085] Although the invention has been explained herein using examples of embodiments and drawings, these do not limit the scope of the invention as defined by the claims. Within said scope, many variations, combinations and extension are possible, as shall be appreciated by the skilled person having the benefit of the present disclosure. For example, the winch as described herein may be operated to provide additional attenuation of tension fluctuations, in particular with respect to relatively low-frequency oscillations. More generally, active attenuation of tension fluctuations, including optionally using the damper assembly, may be applied in addition to the passive attenuation as described herein. Attenuation of tension fluctuations may comprise pre-tensioning and / or pre-relaxing of the tugger line in anticipation of upcoming fluctuations induced by movement of the load with respect to the winch, e.g. shortly before operation of the winch. All such variants are included within the scope of the invention as defined by the claims.

[0086] LIST OF REFERENCE SIGNS

[0087] 1. Offshore vessel

[0088] 2. Monopile

[0089] 3. Tugger line system

[0090] 4. Offshore crane system

[0091] 5. Tugger line

[0092] 6. Winch

[0093] 7. Load bearing part

[0094] 8. Damper assembly

[0095] 9. Hoist line

[0096] 10. Crane block

[0097] 11. Gantry trolley

[0098] 12. Gantry crane

[0099] 13. Crane boom

[0100] 14. Crane pedestal

[0101] 15. Deck

[0102] 16. Hammer tool

[0103] 17. Main crane

[0104] 18. Flange monopile upending tool

[0105] 19. Hydraulic or pneumatic circuit

[0106] 20. Piston-cylinder assembly

[0107] 21. Cylinder

[0108] 22. Piston

[0109] 23. High-pressure end

[0110] 24. Low-pressure end

[0111] 25. Relief valve

[0112] 26. One-way valve 27. Accumulator

[0113] 28. Line connector

[0114] 29. Sheave

[0115] 30. Line connecting load to crane block C. Cylinder axis

[0116] D. Disturbance force on load

[0117] L. Load

[0118] R. Effective reeving length for tugger line

[0119] T. Tension in tugger line W. Working length of tugger line

Claims

Claims1. Tugger line system for stabilization of a load suspended in an offshore crane system, comprising: a tugger line to be engaged with the load; a winch fixed or fixable in the offshore crane system and configured to reel the tugger line in or out from the winch so as to vary a working length of the tugger line; and a damper assembly engaged or engageable with the tugger line between the winch and the load, wherein the damper assembly, when engaged, is configured to passively attenuate fluctuations of tension in the tugger line, said fluctuations being induced by movement of the load with respect to the winch.

2. Tugger line system according to claim 1, wherein the damper assembly, when engaged, is configured to bias the tension in the tugger line to below a predefined tension threshold.

3. Tugger line system according to claim 1 or 2, wherein the damper assembly, when engaged, is configured to reduce an effective reeving length for the tugger line when the tension in the tugger line exceeds a predefined tension threshold, e.g. the predefined tension threshold of claim 2.

4. Tugger line system according to any of the preceding claims, wherein the damper assembly is configured to attenuate the fluctuations using a passively operated hydraulic or pneumatic circuit of the damper assembly, and / or wherein the damper assembly is a hydraulic or pneumatic damper assembly.

5. Tugger line system according to claim 4, wherein the damper assembly comprises a piston-cylinder assembly comprising a cylinder and a piston movable in the cylinder along a cylinder axis of the cylinder.

6. Tugger line system according to claim 5, wherein one of the piston and the cylinder is engaged or engageable with the tugger line, wherein preferably the other of the piston and the cylinder is fixed or fixable in the offshore crane system.

7. Tugger line system according to claim 6, wherein the damper assembly is arranged to change an effective reeving length for the tugger line by movement of the piston with respect to the cylinder along the cylinder axis, in particular in passive response to a change in the tension in the tugger line.

8. Tugger line system according to claim 7, wherein an end of the cylinder where the piston can move towards to reduce the effective reeving length is defined as a high-pressure end, wherein an opposite end of the cylinder where the piston can move towards to increase the effective reeving length is defined as a low-pressure end.

9. Tugger line system according to claim 8, wherein the damper assembly comprises a relief valve arranged to drain hydraulic or pneumatic fluid from the high-pressure end of the cylinder as pressure of said fluid exceeds a predefined pressure threshold, in particular while otherwise blocking said draining.

10. Tugger line system according to claim 9, wherein: the damper assembly comprises a one-way valve arranged in parallel to the relief valve to allow hydraulic or pneumatic fluid to flow intothe cylinder at the high-pressure end, in particular while preventing draining of hydraulic or pneumatic fluid from the high-pressure end otherwise than via the relief valve; and / or the relief valve is adjustable to selectively allow hydraulic or pneumatic fluid to flow into the cylinder at the high-pressure end.

11. Tugger line system according to any of claims 8 - 10, wherein the damper assembly is configured to allow hydraulic or pneumatic fluid to flow into and out from the low-pressure end of the cylinder, in particular substantially without requiring any minimum pressure of said fluid.

12. Tugger line system according to any of claims 4 - 11, wherein the damper assembly comprises an accumulator arranged to store hydraulic or pneumatic fluid therein, in particular for exchange thereof with the cylinder as defined in claim 5.

13. Combination of one or more tugger line systems according to any of the preceding claims and the offshore crane system.

14. Combination according to claim 13, wherein at least one of the following applies for at least one of the one or more tugger line systems: the winch is fixed to the load bearing part; the damper assembly is engaged with the tugger line; the tugger line is engaged with the load.

15. Combination according to claim 13 or 14, wherein, for at least one of the one or more tugger line systems, the load bearing part is, or is part of: a gantry trolley of a gantry crane of the offshore crane system; a crane boom of the offshore crane system; a crane pedestal of the offshore crane system;a part of an offshore structure, such as a vessel or a platform, on which a movable part of the offshore crane system is supported.

16. Combination according to any of claims 13 - 15, wherein the load is, comprises, or is part of: a monopile or other component for an offshore wind turbine or a foundation therefor; or a hammer tool for hammering a monopile for an offshore wind turbine into a seabed.

17. Combination according to any of claims 13 - 16, configured for the tugger line of at least one of the one or more tugger line systems to be engaged with the load via at least one of: a crane block of the offshore crane system; a monopile upending tool, in particular a flange monopile upending tool; a line connector attached to, or formed as part of, the load.

18. Offshore vessel or structure comprising a combination according to any of claims 13 - 17.

19. Offshore vessel according to claim 18, configured for installation of a monopile for an offshore wind turbine at an offshore installation location, and preferably configured for transport of said monopile to said offshore installation location.

20. Use of a tugger line system according to any of claims 1 - 12 for stabilization of a load suspended in an offshore crane system.

21. Use of a combination according to any of clams 13 - 17 for offshore crane operations, in particular for installation of a monopile for an offshore wind turbine at an offshore installation location.

22. Method of stabilizing a load suspended in an offshore crane system, comprising: engaging a tugger line with the load; using a winch, setting a working length of the tugger line in accordance with a desired position of the load; and passively attenuating fluctuations of tension in the tugger line using a damper assembly engaged with the tugger line between the winch and the load, said fluctuations being induced by movement of the load with respect to the winch.

23. Method according to claim 22, wherein the tugger line, winch and damper assembly are those of a tugger line system according to any of claims 1 - 12.

24. Method according to claim 22 or 23, wherein the passive attenuation comprises at least one of: biasing the tension in the tugger line to below a predefined tension threshold; reducing an effective reeving length for the tugger line when the tension in the tugger line exceeds a, e.g. the, predefined tension threshold; increasing an effective reeving length for the tugger line when the tension in the tugger line is below a, e.g. the, predefined tension threshold; passively operating a hydraulic or pneumatic circuit comprising a piston-cylinder assembly;using a, e.g. the, piston-cylinder assembly, reducing an effective reeving length for the tugger line in passive response to an increase of the tension in the tugger line; using a relief valve, in particular in the hydraulic or pneumatic circuit, limiting an increase of the tension in the tugger line to a, e.g. the, predefined tension threshold.

25. Damper assembly evidently configured as the damper assembly of a tugger line system according to any of claims 1 - 12.

26. Method of providing a tugger line system according to any of claims 1 - 12, comprising: providing an initial tugger line system for stabilization of a load suspended in an offshore crane system, the initial tugger line system comprising: the tugger line to be engaged with the load, and the winch fixed or fixable in the offshore crane system and configured to reel the tugger line in or out from the winch so as to vary a working length of the tugger line; and retrofitting a damper assembly according to claim 28 in the initial tugger line system so as to be engaged or engageable with the tugger line between the winch and the load.

27. Method according to claim 26, wherein the initial tugger line system is part of an offshore crane system of an offshore vessel or platform, in particular for installation of monopiles for offshore wind turbines.

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