METHOD AND DEVICE FOR MEASURING DEFORMATIONS ON DECKS ON OFF-SHORE CONSTRUCTIONS AND JACK-UP ASSEMBLY SHIPS AND 3D STABILISATION SYSTEM COMPRISING THE DEVICE FOR THE CONTROL OF DEFORMATIONS OF THE DECK.

The present invention relates to a method for measuring deformations on decks on off shore constructions jack-up assembly ships and offshore platforms, comprising at least one crane for heavy duty lifting, and of the kind comprising a plurality of support legs for lowering to the seabed and on said support legs, the assembly ship or the offshore platform is supported during operations, e.g. with the crane, and 3D stabilization system comprising the registration system for car- rying out the method, specially designed to control of deformations of the deck.

In the following, for the sake of convenience, the description of the invention is related to the offshore construction jack up assembly ships, but the invention will also, as indicated in the preamble, may be used on the offshore platforms.

Construction jack-up assembly ships has been more common with the extraction of raw materials on the territorial sea, and well as the establishment of wind turbines there. Said assembly ships are used for repair work on offshore platforms or at installation and servicing of offshore wind turbines.

Said assembly ships are designed for handling heavy cargo, which often during the voyage to installation on the site, is located on the ship's deck, and which cargo, after arriving to the site, is to be lifted into place, using the or the cranes present on mounting ship. Said cranes may for example have a lifting capacity of more than 1000 tons, and the handling of goods in this order of magnitude, it is inevitable that the removal of deck load of this magnitude, tensions in the deck construction, if no compensating of the support of the deck is carried out, will be able to damage the hull of the vessel. The compensation according to the prior art is performed by measuring the load on the support legs on which the ship is carried on during performing operation with the crane, and on the basis of said measurements to perform a stabilization of the deck lowering or raising one or more of the support legs on which the ship is carried. However, it has been found not to be an appropriate way to perform the stabilization of the stress on the deck, since it is impossible here to take in account whether one or more of the support leg in which the ship or the crane is supported, is deflecting. In US 2009/0090191 A1 (Lenders et al.) is disclosed a prior art technique for surveillance of the support leg on offshore oil rigs comprising a plurality of support legs, where the pressure on the support legs is controlled by means of a rack and pinion drive with motor and gear system on each support leg. The surveillance system comprises a strain surveillance monitoring device, comprising a strain measuring device on a selected sprocket on each rack and pinion, which jointly define a rack path system for surveillance of the difference of rotation of the selected pinions, which provides an indication of the linear displacement of the selected pinions to compare and specify the difference between the position of the support legs on the platform.

The optimal operation conditions for deck cargo and the crane is, that the deck at all time is held in horizontal position or in a position which within very small margins is horizontal. This to avoid excessive torques on the support of the crane and to avoid damages on the deck and hull of the ship. Tensions arising in the deck/hull generates normally relative small height differences on it, and thus, said height differences may be very difficult to detect visually, and when they finally become visible, it is often too late to compensate for these, as the deck and hull already might have deformed itself permanently, with weakening of the construction of the deck/ship as consequence. It is therefore very important that compen- sating of the stress distribution is performed even by small deformations occurring by load changes on the deck, so that the level of tension on the deck always is held within the tolerances applicable for the materials comprised by the construction, and be able to compensate by performing a relative displacement of the re- spective support legs relative to the deck, before strain occurs in the materials comprised be the deck structure. Inclinometers might be used for measuring the inclination of the deck with respect to the horizontal but these measurements will only indicate that a deformation has already taken place, but not indicate the loca- tion of it on the deck.

The most suitable way of performing register of deformations of the deck will be by carrying out an absolute measurement of the position of the deck relative to horizontal, or relative to the initial/reference position of the deck, and it is the ob- ject of the invention to provide a method to make such a measurement. It is further the object of the invention to provide a measurement device for performing such a measurement. Further it is the object to provide a device for automatic 3-D stabilization of the deck on said ships in which the method and the measuring device is used.

It is by the invention realized that the performance of an absolute measurement of the position of the deck, and thus deformations of the deck on offshore construction jack up assembly ships and offshore platforms, comprising at least one crane for lifting of heavy cargo, and of the kind that comprises a plurality of support legs for lowering to the seabed, and on said support legs, in lowered position on the seabed, the assembly ship or the offshore platform is supported during operations, e.g. with the crane, advantageously can be performed by a method in which relative displacements of the level of selected positions of the deck on a jack-up assembly ship og an offshore platform, on the basis of a reference level, in which the deck is in rest an balance and not burdened with deck cargo is measured by free ends of fluid filled tubes arranged in the selected positions, the opposite ends of said tubes are connected to a number of manometers each with a pressure transducer for digital registration of the pressure shown on the manometers, said manometers and pressure transducers being arranged in a row and in mutual same level and parallel with a zero reference plate, arranged symmetrically in the vertical length plane of the assembly ship or the platform, and which manometers is reset with respect to the zero reference plate. It is hereby achieved an absolute measurement of vertical deviation of the deck based on changes in the pressure measured on one or more of the manometers or pressure transducers of the measuring unit. Thus, it will be important, that the manometers are calibrated under quiescent conditions, so that a zero refer- ence level for all measure points are fixed before the deck is loaded with cargo. Said measurements of even small deformations of the deck reveals immediately whether the deck is on torque load, provides the opportunity to perform an immediate regulation of the strain conditions from a knowledge of exactly where the deformations of the deck is located.

A measuring device for the measurement of deformations on the deck of the offshore construction jack up assembly ships and offshore platforms, comprising at least a crane for lifting heavy loads, and of the kind comprising a plurality of support legs intended for immersion in the sea bed and on which support legs, in its lowered position on the sea floor, the assembling the ship or platform is carried during operation, e.g. with the crane, for carrying out the method according to claim 1 is characterized in that the device comprises at least a to the number of support legs corresponding, closed, fluid-filled tube the free ends of which are arranged in measurement points near the supporting legs and in the other meas- urement points of interest in connection with the deck of a jack-up assembly ship or offshore platform, and whose opposite ends are connected to the manometers in a pressure measurement station, comprising a to the number of preferred points of measurement, a number of precision manometers with associated digital/analog pressure transducers, mounted in mutual same level on a console which extends parallel to the deck and parallel to a zero reference plate placed symmetrically in the longitudinal vertical plane of the assembly ship or platform, said gauges being zero adjustable in relation to the zero reference plate.

Using the measuring device, it is hereby possible to detect even very small stresses in the deck structure which results in even very small deformations of the deck, as a vertical displacement of the deck relative to the reference level immediately will reveal itself by a change of the pressure shown on the manometers and the associated pressure transducers. These measurements can be used as basis for decisions to make compensatory offsets relative to the deck of one or more of the support legs are braced on the seabed and carrying platform or the assembly ship, at a level above sea level, with the intention to make the deck plane, and reduce tension in this.

It is preferred that the measure device comprises manometers of a quality which enables detection of a deviation from the 0-reference point of +/- 0,001 m, corresponding to detection of a pressure within a range between 5 mbar and 1000 mbar, typical within the range 12,5 and 250 mbar, and preferred within the range 5 mbar and 100 mbar.

In the intent to minimize the reaction time of the measuring system on an occurring deformation of the deck, it is preferred to use a fluid in the tubes with a low viscosity, thus it is preferred that the viscosity of the fluid at 40°C in the fluid-filled tubes is located within the range of 2 cSt and 9 cSt, typical within 5,5 cSt and 7 cSt and preferred within the range 6,0 cSt and 6,8 cSt.

With intent of further reduction of the reaction time on an occurred deformation of the deck/structure, it is preferred that the resistant figure in the tubes used for the fluid-filled tubes of the measurement system is located within the range 0,05ra and 0,7 ra, typically within the range 0,1 ra and ,05 ra, and preferred within the range 0,2 ra and 0,4 ra.

The compensating displacements may be performed manually by an opera- tor monitors the digital output from manometers and pressure transducers, and that the operator on basis of data performs adaptations of the positions of the support legs relative to the deck. However, said manual operation could be saved, if a control unit is coupled to the measurement device, as it appears from the following.

With the intent to perform an automatic 3D stabilization/tension compensation in the deck there is according to the invention provided a device for automatically 3D compensate system for the deck of the offshore construction jack up assembly ships and offshore platforms and comprising the in claim 2 defined meas- urement device, which further is characterized in that the pressure transducers via the interface is connected to a first processing unit that includes a first software for recording and processing of collected data against pre set limits of vertical displacement of the deck level, stored in the first processing unit, if exceeded will cause recordation of data via interface from at least one inclinometer located on the zero reference plate, and in the event of fluctuations of the inclinometers, the processing unit generates a signal with information concerning the position of the deformation of the deck and the magnitude of the deformation/deformations (ΔΗΑ, ΔΗΒ) relative to the 0-reference level, which signal via the interface is transmitted to another data processing unit with a different software which via interface perform regulation of the relevant supporting legs position relative to the deck, by means of jacks, while the other processing unit at fixed intervals, receives data from the first data processing unit concerning the level of the measuring positions so that the displacements of the deck level are brought within the predetermined limits relative to the 0-reference plane, after which the regulation of relevant support legs position relative to the deck with relevant jacks, are ceased.

Hereby is provided an automatic 3 D stabilizing / tension equalization system, using the method according to the invention for measuring the height differences at selected points in a deck structure in relation to a reference level, and by a measuring device for carrying out the method, in combination with data processing devices with resident software that is interconnected with interface, and connected to the regulation devices of the support legs, whereby stresses and deformations in the deck on the assembly ships and platforms, mounted on the support legs immersed and supported on the sea bed, in operation with a heavy load and general cargo on the deck by one or more cranes, may be compensated automatically to avoid deformations of the deck of the kind that is causing permanent deformations of the deck, and possibly also to the deck corresponding structure .

The invention is briefly explained in the following referring to the drawing, wherein;

Fig. 1 shows a schematic top view of a deck / vessel, for example, on an offshore platform or an assembly ship in which the measurement device according to the invention for measuring the level of the deck at different positions near the support legs are shown,

Fig. 2 is the schematic side view of the Fig. 1 showed deck/vessel is not loaded position, corresponding to 0-reference position, where all measuring positions show the same scale of the to the respective manometers/pressure transducers, Fig. 3 is a schematic side view of the Fig. 1 and Fig. 2 shown deck at load position where the deck slopes and where the responses of manometers/pressure trans- 5 ducers level meters are illustrated,

Fig. 4 is an example of the location of one of the free ends of the measuring tubes, belonging to the measuring device according to the invention, and

Fig. 5 shows a schematic perspective view of a deck, comprising the measure device according to the invention, connected to a data processing unit which controls l o the displacement of the platform support legs.

Fig. 1 shows a schematic top view of a deck/vessel 2, for example on an offshore platform or a assembly ship on which an embodiment of the measuring device 4 according to the invention for measuring the level of the deck 2 in different 15 positions 6, 8, 10, 12, 14, 16, near the supporting legs 18, 20, 22, 24, 26, 28, are shown.

The measuring device 4 comprises in the shown embodiment a plurality of fluid-filled tubes 30, 32, 34, 36, 38, 40, whose free ends are disposed in the afo-

20 rementioned positions 6, 8, 10, 12, 14, 16, near the supporting legs 18, 20 , 22, 24, 26, 28. The free ends of the tubes are closed off by valves, not shown. The other ends of the fluid-filled tubes 30, 32, 34, 36, 38, 40, is, as schematically shown in Fig. 1 , connected to a number of the tubes to the corresponding precision manometer with transducers 42, 44, 46, 48, 50, 52 which are arranged sym-

25 metrically in the same level above or below a reference 0-plate 53 for the

deck/vessel.

Fig. 2 is a schematic side view of the deck/vessel 2, shown in Fig. 1 , in non loaded position, corresponding to the 0 reference position in which all measure- 30 ment positions 6, 8, 10, 12, 14, 16, near the supporting legs 18, 20, 22, 24, 26, 28, shows the same scale, illustrated by the dotted line 54 on the manometers and pressure transducers 42, 44, 46, 48, 50, 52. The deck/vessel is horizontally oriented in the position shown and the dotted line 54 is here an expression of the 0- reference level.

35 Fig. 3 is a schematic side view of the deck/vessel shown in Fig. 1 and Fig. 2, in loaded position in which the deck 2 is inclined, and wherein the signals recorded on the manometers/pressure transducers 42, 44, 46, 48, 50, 52 are illustrated by lines 56, 58, 60, 62, 64 , 66 with respect to the dotted line 54 marking the 0 refer- ence level. As it is apparent from the illustration, the level of the vessel/deck 2, measured on the manometers/pressure transducers 42, 44, in the measurement points 6, 12 (see. Fig. 1) is located higher than the 0-reference level 54. The level of the vessel/deck 2, measured on the manometers/pressure transducers 46, 48 at the measurement point 8, 14 (see. Fig. 1) are located approximately in the 0 refer- ence level 54, and the level of the vessel/deck 2, as measured on the manometers/pressure transducers 50 , 52 at the measurement points 10, 16 (see. Fig. 1) is situated below the 0-reference level 54, and it is clearly seen that the deck 2 is inclined. Fig. 4 is an example of the location of one of the free ends of the fluid-filled tube 30, 32, 34, 36, 38, 40 in one of the positions 6, 8, 0, 12, 14, 16, near one of the support legs 18 , 20, 22, 24, 26, 28, belonging to the measuring device 4 according to the invention. The 0-reference level 54 is shown again, this time at a line 54' extending parallel to the deck 2.

Fig. 5 shows a device 60 for automatically compensating 3D system for the deck 2 of the offshore construction jack up assembly ships and offshore platforms and comprising the measuring device 4 according to the present invention.

The pressure transducers 42, 44, 46, 48, 50, 52 is connected to a first processing unit 62 via the interface 61 c.f.. Fig. 4 and Fig. 5, said first processing unit 62 includes a first software for recording and processing of data collected from the pressure transducers 42, 44, 46, 48, 50, 52 and perform comparison of the collected data relative to limit-values for vertical level displacement of the deck 2 set in the processing unit 62, said limit values, if exceeded, will lead to collection of data through interface from at least one inclinometer 64 placed on the zero reference plate 53, and in the event that inclinometers 64 shows output, the data processing unit 62 generates a signal that via the interface 63 is transmitted to a second data processing-processing unit 66 with a second software which via interface 68, 70, 72, 74, 76, 78 (see. fig. 5), perform control/regulation of the displace- ment of the support legs 42 , 44, 46, 48, 50, 52 with respect to the deck 2, -about position 6, 8, 10, 12, 14, 16 of the deformations of the deck 2, and the amount of the deformation/deformations curve ΔΗΑ, ΔΗΒ in relation to the 0-reference level 54, after which, the second data processing unit 66 perform calculation of the required displacement of the support legs 42, 44, 46, 48, 50, 52 relative to the deck 2, and via interface, carries out regulation of the position of relevant supporting leg(s) 42, 44, 46, 48 , 50, 52 with respect to the deck 2 by the jacks 80, 82, 84, 86, 5 88, 90, while the second data processing unit 66 at fixed intervals, receive data from the first data processing unit 62 concerning the level of the measuring positions 6, 8, 10, 12, 14, 16, so that the displacements of the deck level by means of the jacks 80, 82, 84, 86, 88, 90, are brought within the predetermined limits with respect to the 0 reference plane 54 and if affirmative, the regulation of relevant i o supporting leg position relative to the deck is ceased.

A precondition for correct operation of the measuring device according to the invention, as well as for correct functioning of the automatic 3D stress compensating system is that the reference level 54 for the measuring system has been dels termined before sailing out to the operation position of the platform or the assembly ship.

It should be noted that the inventor has recognized that the number of measurement points for recording changes of the deck level may be more than those

20 indicated in the foregoing, as he also is aware that the resident software in the second data processing unit should include relevant software, customized to the vessel, platform or assembly ships static and dynamic properties. This however, does not alter the inventive aspect that concerns a new way to detect even very small height variations on platforms and decks that can be used for a preventive

25 stabilization of exposed tensions of the deck during handling large loads on this, for example with cranes.