The invention relates to a method for determining a leg load which acts on a support leg of a jack-up vessel, said support leg being lowerable by means of a rack and pinion drive, as well as a lifting device for a lowerable support leg of a jack-up vessel.
In this case, so-called jack-up vessels and jack-up platforms are combined together in the term “jack-up vessels”. Here, a jack-up vessel is understood as a vessel with a separate drive which has lowerable support legs (so-called jack-up legs), on which it is able to be positioned on the floor of a body of water. “Jack-up platform” is understood as a floating platform without a separate drive which has lowerable support legs, on which it is able to be positioned on the floor of a body of water. Jack-up vessels are used, for example, for erecting offshore wind energy plants or offshore drilling platforms for the production of oil or natural gas.
“Lifting device for a lowerable support leg of a jack-up vessel” is understood as a device by means of which the support leg may be lowered to the floor of the body of water and lifted up therefrom.
Both during and after the positioning of the support legs of a jack-up vessel on the floor of a body of water, it is extremely useful to provide information and monitoring of the leg loads respectively loading the support legs as accurately as possible in order to achieve, to monitor and to reproduce if necessary a secure foundation of the jack-up vessel on the floor of the body of water.
The object of the invention is to specify an improved method for determining a leg load which acts on a support leg of a jack-up vessel, said support leg being lowerable by means of a rack and pinion drive. The object of the invention is also to specify a lifting device for a lowerable support leg of a jack-up vessel which permits improved determination of a leg load acting on the support leg.
The object is achieved according to the invention with regard to the method by the features of claims 1 and 11, and with regard to the lifting device by the features of claim 7.
Advantageous embodiments of the invention form the subject matter of the subclaims.
A leg load which acts on a support leg of a jack-up vessel, said support leg being able to be lowered by means of a rack and pinion drive, is determined by means of the method according to the invention, wherein the jack-up vessel has a supporting structure for at least one gear unit of the rack and pinion drive. In this case, at least one strain gauge is arranged on the supporting structure for detecting the strain in the supporting structure caused by the leg load. Strain in the supporting structure is detected by means of the at least one strain gauge and the leg load is determined from the detected strain.
The method according to the invention makes use of the fact that a leg load acting on a support leg produces stresses in the supporting structure as the supporting structure is coupled to the support leg via one or more gear units of the rack and pinion drive. The stresses in the supporting structure cause strain in the supporting structure which are detected according to the invention by means of at least one strain gauge and evaluated for determining the leg load.
According to the invention, therefore, a supporting structure which is fixedly connected to the jack-up vessel is used as a primary sensor element for determining the leg load by means of strain gauges. This has advantages relative to the use of mobile or movably suspended structures, such as for example torque measuring shafts on pinion shafts of gear units of a rack and pinion drive, in that a more robust construction is used whereby the sensitivity to interference of the measurements is reduced and the measuring accuracy increased. Moreover, the determination according to the invention of leg loads acting on a support leg of a jack-up vessel by means of strain gauges arranged on the supporting structures is substantially simpler and more cost-effective than, for example, methods which use expensive and sensitive load cells or torque measuring shafts.
One embodiment of the invention provides that a plurality of strain gauges are arranged on the supporting structure and electrically connected together such that measuring signals of these strain gauges caused by bending stresses and/or torsional stresses and/or temperature changes in the supporting structure mutually compensate one another.
As a result, merely by a suitable arrangement and connection of the strain gauges, it is advantageously achieved in a simple manner that bending stresses or torsional stresses or temperature changes in the supporting structure do not falsify or unnecessarily complicate the determination of the leg loads.
Preferably, at least one pair of strain gauges is arranged on the supporting structure such that the strain gauges of the pair detect the strain in the supporting structure in different directions and the strain gauges of each pair are electrically connected to a half bridge.
As a result, it is achieved for example that strain in the supporting structure produced by temperature changes does not influence the measurement result, as temperature changes generally cause strain irrespective of the direction and therefore may be compensated by the variable alignment of two strain gauges connected to a half bridge.
One embodiment of the invention provides in this case that at least two pairs of strain gauges electrically connected to a half bridge are arranged on the supporting structure such that the strain gauges of each pair detect the strain in the supporting structure in different directions and in that the strain in the supporting structure detected by different pairs is averaged for determining the leg load.
By averaging the measurement results of at least two different pairs of strain gauges connected to a half bridge, it is advantageously possible to reduce measuring errors which are caused by stresses occurring sporadically and locally at the locations of individual strain gauges.
A particularly preferred embodiment of the invention provides that at least two pairs of strain gauges electrically connected to a half bridge are arranged on the supporting structure such that the strain gauges of each pair detect the strain in the supporting structure in different directions, and such that at least two of these pairs are electrically connected to a Wheatstone full bridge for detecting the strain in the supporting structure caused by the leg load.
As a result, the known advantages of the Wheatstone bridge circuit may be used for improving the measuring accuracy and for compensating for bending stresses and torsional stresses and temperature effects. Thus, when using the same strain gauges, the measurement voltage of the Wheatstone full bridge disappears if all of the strain gauges are unexpanded. If, however, some of these strain gauges are expanded or compressed, the measurement voltage generally alters to positive or negative values as a result of alterations to the electrical resistances of the strain gauges caused by the strain. The different alignment of the two strain gauges in the half bridges of the full bridge permits the reduction of measurement errors which are caused by bending stresses or torsional stresses or temperature changes.
A further embodiment of the invention provides that each strain gauge is arranged on a supporting structure region of the supporting structure which is free from notch stresses.
“Notch stresses” in this case are understood as excess stresses in the supporting structure which occur at notch-like weak points (including weld seams) of the supporting structure.
The arrangement of the strain gauges on supporting structure regions which are free from notch stresses has the advantageous effect that the measurements of strain in a supporting structure are not influenced by such notch stresses.
A lifting device according to the invention for a lowerable support leg of a jack-up vessel, wherein the support leg has at least one toothed rack extending parallel to a longitudinal axis of the support leg, comprises a rack and pinion drive having at least one gear unit for a toothed rack of the support leg, a supporting structure which has at least one supporting frame on which at least one gear unit of the rack and pinion drive is arranged and a measuring device for determining a leg load acting on the support leg. In this case, the measuring device comprises at least one strain gauge arranged on a supporting frame for detecting the strain in the supporting frame caused by the leg load and a control unit electrically connected to the at least one strain gauge for determining the leg load from measuring signals of the at least one strain gauge.
The lifting device according to the invention permits the use of the method according to the invention for determining the leg load from measuring signals with the above-mentioned advantages in that it comprises a corresponding measuring device. The lifting device thus permits an improved determination and monitoring of the respective leg loads loading the support legs, during and after the positioning of the support legs of a jack-up vessel on the floor of a body of water, and thereby improves the security of the foundation of the jack-up vessel on the floor of the body of water.
One embodiment of the lifting device provides that at least one supporting frame has a rear wall and two side walls angled back from the rear wall, wherein at least one gear unit of the rack and pinion drive is arranged on the rear wall and at least one strain gauge of the measuring device is arranged on each side wall.
This embodiment of the lifting device is particularly advantageous if the side walls have supporting structure regions which, on the one hand, are free of notch stresses so that the measurements are not influenced by such notch stresses and in which, on the other hand, stresses which are as high possible are nevertheless produced by a leg load in order to achieve sufficient measuring accuracy.
In this case, at least one pair of strain gauges of the measuring device electrically connected to a half bridge is preferably arranged on each side wall of at least one supporting frame.
Particularly preferably, in this case at least two pairs of strain gauges connected to a half bridge and arranged on different side walls of a supporting frame are also electrically connected to a Wheatstone full bridge.
These arrangements and connections of the strain gauges have the aforementioned advantages that they permit the influences of bending stresses, torsional stresses and/or temperature changes to be compensated.
The invention provides, in particular, the use of the method according to the invention for determining a leg load which acts on a support leg of a jack-up vessel, said support leg being lowerable by means of a lifting device according to the invention, wherein the leg load is determined by means of the measuring device of the lifting device.
The above-described properties, features and advantages of this invention and the manner in which they are achieved become clearer and more easily comprehensible in association with the following description of exemplary embodiments which are described in more detail in combination with the drawings, in which:
Parts which correspond to one another are provided with the same reference numerals in all of the figures.
The deck 1 has a substantially rectangular contour with four corners. In the vicinity of each corner, the deck 1 has a deck opening 4 for passing through a support leg 5 and a lifting device 3 for lowering and lifting this support leg 5.
Each support leg 5 is configured as a lattice-like framework structure, the envelope thereof approximately having the structure of a prism with a triangular footprint. Each support leg 5 has three toothed racks which extend parallel to one another, in each case along one of the three vertical support leg edges 6 of the support leg 5.
Each lifting device 3 comprises a rack and pinion drive cooperating with the toothed rack of the respective support leg 5, for lowering and lifting the support leg 5. The rack and pinion drive for each toothed rack of the support leg 5 has eight gear units 7, not shown in more detail in
Two strain gauges R1 to R4 of a measuring device 15 (see
In this case, the four strain gauges R1 to R4 for a supporting structure 8 are electrically connected together, as shown in
In
The measuring device 15 in this case advantageously makes use of the fact that a leg load which acts on the support leg 5, causes stresses in the supporting structure 8 via the gear units 7 arranged on the supporting structure 8 which in turn cause strain in the supporting structure 8. This strain is detected by the strain gauges R1 to R4 arranged on the supporting structure 8, and by means of the control unit 16 the leg load acting on the support leg 5 is determined from the detected strain. The Wheatstone full bridges W function in this case in the known manner by exploiting the alterations to the electrical resistances of the strain gauges R1 to R4 caused by the strain. Thus when using the same strain gauges R1 to R4, a zero measurement voltage UM is produced on the Wheatstone full bridge W if all of the strain gauges R1 to R4 are unexpanded. If, however, some of these strain gauges R1 to R4 are expanded or compressed, the measurement voltage UM generally alters to positive or negative values.
In this case, the above-described arrangements, in particular the variable alignment of the two strain gauges R1 to R4 in the half bridges H1, H2 as well as the electrical connection of the strain gauges R1 to R4, have the result that measuring signals of these strain gauges R1 to R4, caused by bending stresses or torsional stresses or temperature changes in the supporting structure 8, mutually compensate one another so that leg loads which act on the support leg 5 substantially only in vertical directions are advantageously detected by the Wheatstone full bridges W.
The strain gauges R1 to R4 are also arranged on the supporting structures 8 such that they are located in supporting structure regions A to D of the supporting structures 8 which, on the one hand, are free from notch stresses so that the measurements of the strain in the supporting structures 8 are not influenced by such notch stresses and in which, on the other hand, stresses which are as high as possible are produced by a leg load in order to achieve sufficient measuring accuracy. In order to determine such supporting structure regions A to D, preferably a simulation of the stress distribution produced by a leg load in a supporting structure 8 is carried out, for example, by means of a corresponding finite element analysis of the stress distribution.
Although the invention in detail has been illustrated and described more specifically by a preferred exemplary embodiment, the invention is not limited by this disclosed example and other variants may be derived therefrom by the person skilled in the art without departing from the protected scope of the invention. In particular, for example, the measuring signals of the two half bridges H1, H2 arranged on the different side walls 12, 13 of a supporting structure 8 may be separately detected and determined by strain gauges R1 to R4, without the half bridges H1, H2 being connected to form a Wheatstone full bridge W. Alternatively or additionally, one respective temperature sensor may be arranged in the vicinity of these half bridges H1, H2, in order to detect temperatures in the supporting structure 8 and to identify strain caused by temperature changes and, if required, to incorporate said strain in the evaluation of the measurement results. Naturally, the invention is also not limited to the application to jack-up vessels 2 which have four lowerable support legs 5 and a deck 1 with a rectangular contour as in the described exemplary embodiment, but is similarly applicable to jack-up vessels 2 with a different number of lowerable support legs 5 or a different shape of deck 1, for example, to jack-up vessels 2 with three support legs 5 and a deck 1 with a triangular contour. Also, the number of gear units 7 of the lifting device 3 is not relevant to the invention, i.e. the invention also relates to lifting devices 3 having different numbers of gear units 7.
Number | Date | Country | Kind |
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10 2012 217 880.5 | Oct 2012 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/070400 | 10/1/2013 | WO | 00 |