Lifting tool

A lifting tool for lifting an element of an offshore structure, such as a transition piece of an offshore wind turbine comprises a frame and a plurality of engagement members for engaging an element to be lifted. The engagement members are mounted to the frame at an angular distance from each other about a centerline of the frame. The lifting tool also comprises a hoisting member to be connected to a hoisting cable of a crane, and located within a virtual cylinder on which the engagement members lie. The hoisting member and the frame are interconnected rigidly through at least three linear actuators which are arranged such that the hoisting member is movable with respect to the frame in a plurality of radial directions with respect to the centerline, independently from the engagement members.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application of International Application No. PCT/NL2019/050223, filed Apr. 17, 2019 and published as WO 2019/209103 on Oct. 31, 2019, in English.

BACKGROUND

The present invention relates to a lifting tool for lifting an element of an offshore structure, such as a transition piece of an offshore wind turbine.

Most offshore wind turbines use a monopile foundation on which a transition piece is placed. The turbine and its tower are mounted onto the transition piece. Transition pieces are being lifted by connecting a lifting tool to a hoisting cable of a crane, on the one hand, and to the transition piece, on the other hand. It is important to align the lifting tool with the center of gravity of the transition piece. Otherwise the transition piece may suspend inclined from the hoisting cable of a crane and/or the transition piece may start swinging upon lifting it. The same effect may happen with other elements to be lifted.

SUMMARY

A lifting tool quickly and accurately aligns with the center of gravity of an element to be lifted. The lifting tool comprises a frame, a plurality of engagement members for engaging an element to be lifted, which engagement members are mounted to the frame at an angular distance from each other about a centerline of the frame, a hoisting member to be connected to a hoisting cable of a crane, and located within a virtual cylinder on which the engagement members lie. The hoisting member and the frame are interconnected rigidly through at least three linear actuators which are arranged such that the hoisting member is movable with respect to the frame in a plurality of radial directions with respect to the centerline, independently from the engagement members.

An advantage of the invention is that the position of the hoisting member can be adjusted with respect to the frame in different radial directions. The invention provides the opportunity to control the alignment in an automatic way by operating the individual linear actuators. This works quickly and is also safe since operators can stay away from the lifting tool upon aligning the lifting tool. The lifting tool may be provided with sensors to measure acceleration/motion, position, gravity, vibration, pressure, etc. in order to facilitate automatically aligning and positioning in horizontal and vertical direction. The relative position of the hoisting member may be adjusted before starting a hoisting action on the basis of a calculated or measured center of gravity of an element to be lifted.

The rigid interconnection allows to guide a pushing force between the frame and the hoisting member, which is different from a cable connection, for example, which cannot guide a pushing force. Under operating conditions the centerline of the frame is directed upwardly or substantially vertical and the engagement members may lie in a horizontally oriented plane. The centerline of the frame may coincide with a centerline of the virtual cylinder.

Preferably, the actuators are coupled to the frame at the engagement members in order to minimize any distance between an engagement member and a location of the frame on which a hoisting force is exerted.

The hoisting member may be located above the frame under operating conditions of the lifting tool.

In a particular embodiment the hoisting member and the frame are interconnected through three linear actuators which are positioned at equiangular distance about the hoisting member when the hoisting member is located at the centerline. This arrangement provides the opportunity to move the hoisting member in all radial directions with respect to the centerline, which avoids the need to position the lifting tool at a predetermined rotational position with respect to the element to be lifted.

Each of the linear actuators may be pivotally mounted to the hoisting member through a first pivot and pivotally mounted to the frame through a second pivot.

In a particular embodiment each of the linear actuators extends substantially perpendicular to the centerline, wherein the first pivot and the second pivot have respective pivot axes which extend substantially parallel to the centerline. This is a rather simple and robust structure.

Alternatively, the linear actuators may form a tripod. A hexapod structure may be conceivable, as well.

In practice the linear actuators may comprise hydraulic cylinders.

The engagement members may be provided with respective supporting elements including upwardly directed supporting surfaces for engaging cooperating lifting plates of an element to be lifted, wherein the frame is provided with a driving device for rotating the lifting tool with respect to an element to be lifted so as to move the supporting elements to a position below the lifting plates. In this case, the supporting elements of the lifting tool and the lifting plates of an element to be lifted form a bayonet coupling.

The driving device may be formed by a drivable driving wheel which is movable in radial direction of the centerline in order to engage and disengage the driving wheel to and from a tube of the element to be lifted when the element to be lifted is provided with a tubular portion.

The supporting elements may be directed to the centerline of the frame such that they can engage outwardly directed lifting plates of an element to be lifted. Such outwardly directed lifting plates are advantageous when the element to be lifted is a transition piece of an offshore wind turbine, for example, since the upper side of a transition piece is often provided with a protection lid for temporarily protecting devices in the transition piece. When outwardly directed lifting plates are applied the protection lid can stay on the transition piece during a hoisting action.

The lifting tool may be provided with an alignment apparatus, which comprises a camera that is positioned such that a view line of the camera extends in the same direction as the centerline of the frame, and a control device for receiving and processing a signal from the camera, which is configured such that, when a transition piece is to be mounted to a monopile by the lifting tool and the transition piece approaches the monopile, the control device determines at least two circumferential images of the monopile along its length on the basis of the camera signal, for example an upper edge and a lower edge of the monopile, and respective imaginary circumferential images having fixed positions at different locations along the view line of the camera and shows the images to an operator via a user interface. The operator may be a crane driver who does not have direct view on the monopile. The crane driver can move the lifting tool including the transition piece such that the circumferential images of the monopile and the imaging circumferential images are moved to each other in order to align the transition piece and the monopile.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG.1shows an embodiment of a lifting tool1. The lifting tool1is suitable for lifting an element of an offshore structure, such as a transition piece2of a wind turbine, or lifting another elongated member including a flange. The transition piece2comprises a tubular element3which can be mounted onto a monopile that is fixed to the sea bottom, for example. The transition piece2is provided with a working platform4that is fixed to the tubular element3. The tubular element3has an upper end which is covered by a protection lid5for temporarily protecting devices (not shown) in the tubular element3. Such devices are intended for use during the operational time of a wind turbine and are already placed inside the transition piece2before it is actually placed off shore. More in general terms, the element to be lifted is a tubular element which comprises a removable protection lid for closing the tubular element.

After installing the transition piece2at its intended location the protection lid5can be removed and a pedestal of a wind turbine can be mounted onto the transition piece2. The lifting tool1is provided with three engagement members6which can engage lifting plates7that are fixed to the upper end of the tubular element3. The engagement members6and the lifting plates7are coupled to each other via a bayonet coupling in this case. The lifting plates7project in outward direction from the transition piece2. This means that the protection lid5can stay on the transition piece2during a hoisting action.

FIG.2shows the lifting tool1in more detail. The lifting tool1comprises a frame8to which the engagement members6are mounted. The frame8lies in a main plane which is oriented horizontally under operating conditions. The engagement members6are located on a virtual cylinder which has a centerline perpendicular to the horizontally oriented main plane of the frame8. The lifting tool1is also provided with a hoisting member9that can be connected to a hoisting cable of a crane (not shown) via a hoisting eye in the hoisting member9. In the embodiment as shown the hoisting member9is located above the frame8under operating conditions of the lifting tool1.

In the embodiment as shown inFIG.2the hoisting member9and the frame8are interconnected through three linear actuators in the form of hydraulic cylinders10which are pivotally mounted to the hoisting member9via respective first pivots11including respective pivot axes that extend perpendicular to the main plane of the frame8. The hydraulic cylinders10extend perpendicular to the centerline of the virtual cylinder and form a rigid connection between the hoisting member9and the frame8. The first pivots11are located at equiangular distance about the hoisting member9. When the hoisting member9is located at the centerline of the virtual cylinder the hydraulic cylinders10extend radially from the hoisting member9at equiangular distance about the hoisting member9. This condition is shown from above inFIG.3.

The hydraulic cylinders10are also pivotally mounted to the frame8via respective second pivots12including respective pivot axes that extend parallel to the pivot axes of the first pivots11. In the embodiment as shown inFIG.2the second pivots12are located at the engagement members6. Due to the arrangement of the hydraulic cylinders10with respect to the hoisting member9and the frame8the hoisting member9is movable with respect to the frame8in all radial directions of the centerline of the virtual cylinder, independent from the engagement members6. This provides the opportunity to easily move the hoisting member9to a location above the center of gravity of the transition piece2before lifting it.

The lifting tool1is provided with driving wheels13, which are mounted to arms14that are pivotally mounted to the frame8at the engagement members6. The arms14are driven by hydraulic cylinders15such that the driving wheels13can be moved to and from the tubular element3of the transition piece2. When driving the driving wheels13after contacting the tubular element3the lifting tool1is rotated with respect to the tubular element3. The latter condition is shown inFIG.4, which illustrates that the frame8has rotated clockwise with respect to the situation as shown inFIG.3. During this movement respective upwardly directed supporting surfaces16of the engagement members6are positioned below the lifting plates7, hence forming a bayonet coupling. This condition is shown inFIG.6.

FIGS.7and8show the operation of the engagement members6in more detail. Each of the engagement members6is provided with an arm17that is pivotally mounted to the frame8via a third pivot18that has a horizontally oriented pivot axis, on the one hand, and that is pivotally mounted to a vertical shaft19of the second pivot12via a fourth pivot20that also has a horizontally oriented pivot axis, on the other hand. The pivot axes of the fourth pivots20lie closer to the hoisting member9than the pivot axes of the third pivots18. Each of the arms17is provided with a locking element28. Upon moving the hoisting member9downwardly with respect to the frame8the engagement members6provide respective openings for receiving the lifting plates7due to displacing the locking element28upwardly. This condition is shown inFIG.7. When the hoisting member9is moved upwardly with respect to the frame8, such as illustrated inFIG.8, the arms17tilt such that the lifting plates7are clamped between the respective supporting surfaces16and downwardly moving locking elements28. As a consequence, the lifting plates7will not bent during hoisting whereas a fixed lifting support during hoisting is achieved. It is noted, that each of the arms17is adapted such that it can rotate through the corresponding third pivot18by only a limited angle due to abutment of a side of the locking element28against an opposite wall at the engagement member6.

FIG.5shows a situation in which the hoisting member9is moved with respect to the frame8, away from the centerline of the virtual cylinder by operating the individual hydraulic cylinders10. The relative position of the hoisting member9may be adjusted before starting a hoisting action on the basis of a calculated or measured center of gravity of the transition piece2. Alternatively, the relative position of the hoisting member9may be adjusted during a hoisting action on the basis of information from sensors on the lifting tool1and/or the transition piece2.

In an alternative embodiment the hydraulic cylinders may form a tripod.FIGS.9and10show a hydraulic circuit of a tripod configuration, in which two of three hydraulic cylinders10are visible.FIG.9illustrates a condition in which the hoisting member9is located at the centerline of the frame8, which is out of line with the center of gravity COG of the transition piece2.FIG.10illustrates a condition in which the hydraulic cylinders10are operated such that the hoisting member9is aligned with the center of gravity COG.

In this embodiment the hydraulic cylinders10are connected to each other in order to use the principle of communicating volumes to distribute the oil pressure in the cylinders10. All three cylinders10are identical and are equipped with brakes and double seals in order to make them fail safe. Furthermore, each cylinder10has a system for releasing the pressure in order to enable soft landing of the lifting tool1. The hydraulic lines between the cylinders10(for creating communicating volumes) contain valves to enable or disable the flow of oil through the system depending on the required orientation (angle) the transition piece2needs to be lifted.

It is noted that under operating conditions the crane hook from which the lifting tool1suspends also needs to be vertically aligned with the center of gravity COG in order to make sure that the transition piece1will not start swinging upon lifting it.

In order to safely and accurately mount the transition piece2on a monopile the lifting tool1may be provided with an alignment apparatus including a camera21and a control device (not shown).FIG.11illustrates the functioning of the alignment apparatus. The camera21may be located on the frame8of the lifting tool1. It is positioned such that a view line22of the camera21extends in the same direction as the centerline of the frame8.FIG.11only illustrates the functioning of the camera21and the control device in general without showing the lifting tool1, the transition piece2and the monopile, but a tube23inFIG.11may be considered as being a monopile.FIG.11shows that along the view line22of the camera21there are a front imaginary circumferential image24and a rear imaginary circumferential image25. Both front and rear imaginary circumferential images24,25have different positions along the view line22and are generated by the control device. When a transition piece2is to be mounted to a monopile by the lifting tool1and approaches the monopile, the camera21also detects a front circumferential image26and a rear circumferential image27of the monopile. In practice the front and rear circumferential images26,27may correspond to an upper rim and a lower rim of the monopile, but other locations along the tube23are conceivable. The control device shows the detected and generated images24-27to a crane driver via a user interface (not shown), for example a mobile phone.FIG.12shows an example of the images as can be seen by the crane driver. On the basis of these images the crane driver can adjust the position and orientation of the transition piece2such that the front imaginary circumferential image24and the front circumferential image26, on the one hand, and the rear imaginary circumferential image25and the rear circumferential image27, on the other hand, form concentric circles, such that the transition piece2and the monopile are aligned. It is noted that in this case the monopile or tube23have circular cross sections, hence resulting in concentric circles, but alternative shapes are conceivable.

The control device may be provided with software for calculating the required movements needed by the crane driver in order to facilitate to obtain concentricity of the images. Since the crane driver can align the transition piece2and the monopile without the necessity of human assistance at the monopile the work can be done in a safe way.

More in general, the invention is also related to a method of aligning a member, for example a lifting tool, with respect to an elongated element, for example a monopile, wherein a camera is mounted to the member to be aligned, wherein the camera is positioned such that its view extends along a view line that, after aligning, substantially coincides with a centerline of the elongated member, wherein the member including the camera is located at a position at or close to an end of the elongated element in which position the elongated element is visible by the camera, such that the camera detects at least two circumferential images of the elongated element located at different locations in longitudinal direction thereof, for example an upper rim and a lower rim of the elongated element, wherein at least two imaginary circumferential images at different positions along the view line of the camera are generated, wherein the member to be aligned and the elongated element are displaced and oriented with respect to each other such that the centers of the imaginary circumferential images substantially coincide with the centers of the circumferential images of the elongated element. The invention is also related to an alignment apparatus that applies this method.

The invention is not limited to the embodiments shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents.