Assembly comprising a first and a second member and a connector, and a method of assembling such an assembly

An assembly includes a first and a second member, where the second member has a fork-shaped cross section with a main body and two substantially parallel walls that each comprise at least one through hole and the first member is arranged between the two walls of the second member, having a through hole. The through hole of the first member and the through holes of the second member define a channel. A connector is axially insertable in the channel to an end position and consecutively expandable radially relative to said channel, to connect the first and second member relative to each other. The connector, in an expanded state thereof, pushes the first member against the main body of the second member to define a pre-tensioned connection between the first member and the second member. A method of assembling a first and a second member.

This is a national stage application filed under 35 U.S.C. § 371 of pending international application PCT/IB2019/056792, filed Aug. 9, 2019, which claims priority to Netherlands Patent Application No. 2021462, filed Aug. 13, 2018, the entirety of which applications are hereby incorporated by reference herein.

The present invention relates to an assembly, comprising a first and a second member, and a connector to connect the first and second member relative to each other.

The invention further relates to a method of assembling such an assembly of a first and a second member that each comprise at least one through hole.

The present invention is particularly suitable for offshore applications, e.g. for connecting a wind turbine to a monopile, a wind turbine to a transition piece, a transition piece to a monopile, as well as between members of a monopile or wind turbine, and jacket connections.

According to prior art applications in offshore, the members of such assemblies are provided with flanges which are connected using bolts of significant size. Currently M72 bolts are used for connecting a wind turbine tower to a monopile or transition piece. In a first step, these bolts are electrically tightened with 8.000 Nm. In a second step, the preload is increased with hydraulic tools to 22.000 Nm. The bolts itself are heavy and the tools for tightening the bolts is also heavy and hard to handle.

It appears that the actual preload on the bolts after some settling time is hard to predict and control, and may vary significantly. Although it is not exactly clear which factors influence the torque-tension relationship of the bolts, it may be concluded that installing the bolts using a “constant torque” method does not achieve satisfying results. Similar issues occur with tensioning systems for bolting. The preload on the bolts must be regularly checked and adjusted, periodically requiring significant maintenance work.

Furthermore, the bolts are arranged all around the circumference of the flanges, leaving only a very limited gap between adjacent bolts. A connection using flanges with bolts is insufficiently scalable to meet the ever increasing demands resulting from even larger wind turbines and greater depths as sea where they are installed.

International patent application WO 2018/139929 A1 of Applicant proposes an assembly that is improved relative to a connection using flanges connected by bolts. This improved prior art assembly comprises:a first and a second section, each comprising a longitudinal axis;a fixation configured to fix the first and the second section;wherein at least one of the first and the second section comprises a body that is configured to be engaged by the fixation; andwherein the fixation comprises an abutment and a radially displaceable actuator.
The actuator is radially displaceable with respect to the longitudinal axis of the section that comprises the actuator. This allows the actuator itself to be employed as part of a clamp. During radial displacement of the actuator, an inclined surface of the actuator engages a specially machined surface of the first section and gradually increases the clamping force that connects the first and the second section. Although the assembly of WO 2018/139929 A1 already provides a significant improvement relative to the above-described prior art connections using flanges connected by bolts, Applicant now proposes even further improvements. Radial displacement of the actuator required a significant force due to the clamping action. Moreover, sections with a specially designed contact surface were required.

The United States patent application US 2008/080946 A1 is directed to an expansion pin system for construction of a wind turbine structural tower, and is considered the closest prior art. It discloses, in terminology of the present invention, a first and a second member, wherein the second member has a fork-shaped cross section with a main body and two substantially parallel walls that each comprise at least one through hole, wherein the first member is arranged between the two walls of the second member, having the through hole, and wherein said through hole of the first member and the through holes of the second member are aligned to define a channel. The expansion pin may be interpreted as a connector that is axially insertable in said channel to an end position and consecutively expandable radially relative to said channel, to connect the first and second member relative to each other. When the expansion pin system is inserted into the channel it results in an alignment of the through holes of the first and the second member.

The European patent publication EP 2187506 A1 discloses a number of adjustable locking devices located between segments of a cylindrical shell of a stator of an electric generator of a wind power turbine. These adjustable locking devices are configured to press the segments together circumferentially and lock the segments in a give position. The device of EP 2187506 A1 fails to disclose a second member that has a fork-shaped cross section with a main body and two substantially parallel walls that each comprises at least one through hole, wherein a first member is arranged between the two walls of the second member, having the through hole.

The expansion bolt of United States patent U.S. Pat. No. 1,120,409 and the anchor bolt disclosed in EP 3171040 A1 are acknowledged as further prior art.

An object of the present invention is to provide an assembly, that is improved relative to the prior art and wherein at least one of the above stated problems is obviated.

Said object is achieved with the assembly according to claim1of the present invention, comprising:a first and a second member, wherein;the second member has a fork-shaped cross section with a main body and two substantially parallel walls that each comprise at least one through hole;the first member is arranged between the two walls of the second member, having the through hole;wherein said through hole of the first member and the through holes of the second member define a channel;further comprising a connector that is axially insertable in said channel to an end position and consecutively expandable radially relative to said channel, to connect the first and second member relative to each other; andwherein the connector, in an expanded state thereof, pushes the first member against the main body of the second member to define a pre-tensioned connection between the first member and the second member.

As a result of the pre-tensioned connection between the first member and the second member any load fluctuations going through the connector are reduced significantly resulting in very low fatigue damage levels compared to a non pre-tensioned connection.

The United States patent application US 2008/080946 A1 fails to disclose that the connector, in an expanded state thereof, pushes the first member against the main body of the second member to define a pre-tensioned connection between the first member and the second member. After all, a male flange end which may be considered the first member, is arranged in between two flanges of a female end of the connector, with a free end of said male flange end being disposed at a distance from the connector. From a perspective of alignment of the holes, as obtained by the expansion pin of US 2008/080946 A1, it makes perfect sense that the male flange end, i.e. the first member, has a free end. However, a perfect alignment is not desired in view of obtaining an optimal pre-tensioning of the connection between the first member and the second member.

Relative to the assembly of WO 2018/139929 (A1), a user may insert a connector into the channel to an end position in a first step, followed by a further step of consecutively expanding said connector radially relative to said channel, to thereby connect the first and second member relative to each other. In this way, the connector may be accurately and easily placed in the channel by a user with very limited hassle or force. Only when the connector is placed in its desired end position, it is expanded in the channel to connect the first and second member relative to each other. Use of a connector according to the invention also makes specially machined contact surfaces with an inclination corresponding to an inclination of the radially displaceable actuator redundant.

Relative to the older prior art of bolted flanges, large scale (e.g. M72) bolts are redundant. Also, the body may be less bulky than a flange comprising through holes to accommodate a bolt. As a result, the assembly according to the invention, requires less material, is therefore more compact and lighter, and also more elegant. Whereas thick parts need to be forged, smaller parts may also be rolled, possibly allowing the members to be formed with alternative and more attractive manufacturing methods. Also, the assembly according to the invention is scalable, providing the opportunity to arrange multiple connectors in axial direction of the members.

A further advantage of the proposed assembly relative to bolted flanges, is the absence of these flanges, that would provide a significant mass outside the path where forces travel during driving the assembly into a ground using a hammer. The mass of conventional flanges may result in bending of the neck of the flanges. These bending stresses currently result in significantly reduced life time of the welds of these flanges when installed with a conventional impact hammer.

An even further advantage of the proposed assembly relative to bolted flanges, is that it may be applied for connecting members under the waterline. On the one hand, longitudinal members of a limited length may be used, allowing smaller ships to transport them to a desired location for an offshore construction.

The successively tightening the bolts of a bolted flange—which are typically tightened in multiple steps, as mentioned above—is very time consuming and labor-intensive. The proposed assembly is less labor-intensive and time consuming than a connection having bolted flanges.

According to a preferred embodiment, the connector, in the expanded state thereof, pushes against faces of the through holes of the second member that are directed away from the main body thereof to define the pre-tensioned connection between the first member and the second member.

According to a further preferred embodiment, in the expanded state of the connector, wherein the connection between the first member and the second member is pre-tensioned, the through hole of the first member is arranged at an offset relative to the through holes in the second member. As mentioned above, said through hole of the first member and the through holes of the second member define a channel, which means that said through holes are positioned in a way that they are “substantially” aligned. However, a preferred offset may guarantee that there always remains a slight misalignment of the through hole of the first member relative to the through holes of the second member. This is advantageous, because the offset, i.e. the slight misalignment in the channel, guarantees that the connection between the first member and the second member may be optimally pre-tensioned. After all, the connector is configured to expand in the channel, wherein the connector pushes the first member against the main body of the second member. In order to optimally push the first member towards the main body of the second member, it is beneficial if the side of the connector that is directed towards the main body does not come into contact with the inner walls of the through holes in the parallel walls of the second member. In this way, the side of the connector that is directed towards the main body can fully transfer its compressive force to the first member that is pressed towards and against the main body of the second member to obtain the desired pre-tensioning.

According to a preferred embodiment, the connector comprises:a compacted state, wherein the connector has a size that is freely insertable into and out of the channel; anda connecting state, wherein the connector is expanded in the channel to connect the first and second member relative to each other.

In the compacted state, play between the connector and the inner wall of the channel allows the connector to be easily inserted into the channel. Afterwards, a high axial clamping force may be provided by the connector, which has the advantage that the assembly is less susceptible for load variations. This is best understood when compared to how a bolted joint carries a direct load. An adequately pretensioned bolt can survive in an application that an untightened, or loose bolt, would fail in a short period of time. The bolt only ‘feels’ a small portion of the applied load.

The invention is furthermore directed to a method of assembling a first and a second member that each comprises at least one through hole, said method comprising the steps of:positioning the through holes of the first and the second member to define a channel;inserting a connector into the channel to an end position;consecutively expanding said connector radially relative to said channel, to thereby connect the first and second member relative to each other; andthe expanded connector pushing the first member against the main body of the second member to define a pre-tensioned connection between the first member and the second member.

In a preferred embodiment, the above mentioned method steps are preceded by the step of positioning at least one of said first and said second member by hoisting thereof, wherein a hoisting equipment engages at least one of the through holes of said respective first or second member. As the connector may be a separate unit that is only inserted into the channel during assembly, the through holes in the first and the second member may be effectively used during hoisting thereof.

In a further preferred embodiment of said method, an elongate member, preferably a rod, is arranged through at least one of the through holes to connect the respective first or second member to the hoisting equipment.

Further preferred embodiments are the subject of the dependent claims.

An example of an offshore construction comprising multiple connections C where an assembly according to the invention may be applied is shown inFIG. 1. An offshore wind turbine tower1is supported by a supporting base structure2which is inFIG. 1embodied as a monopile3with a transition piece4. The skilled person will understand that similar connections are present for alternative supporting base structures2, such as (not shown) jackets.

The connections C may be applied between separate members8of the monopile3, between the monopile3and the transition piece4, between the transition piece4and the turbine tower1, between members9of the turbine tower1, and between a rotor blade6and a hub of a rotor.

During use, a wind turbine5will be oriented such that the rotor blades6are optimally driven by the available wind power. The rotor blades6drive a (not shown) generator in the nacelle7, wherein the generator generates electricity. The wind turbine5causes alternating loads on any connection C in the construction, and dependent on the wind direction, specific parts of the connection C have to absorb most of the loads.

According to the prior art (FIG. 2), an assembly10configured to connect a first member11and a second member12normally comprises flanges13,14. These flanges13,14are provided with through holes15,16, which are aligned. A bolt17and nut40assembly is then arranged through the aligned through holes15,16, and used to clamp the flanges13,14to each other. As already described, currently M72 bolts17are used for connecting a wind turbine tower1to a monopile3or transition piece4. The bolts17itself are heavy and the tools for tightening the bolts17are also heavy and hard to handle. Moreover, the preload on the bolts17must be regularly checked and adjusted, periodically requiring significant maintenance work.

In order to accommodate the through holes15,16and create an effective preload between both flanges13,14, the flanges13,14need to be relatively thick in both axial direction.

In order to prevent that the flange becomes an effective lever when a significant tensile load is applied on the steel wall that is welded to flange14the flange also needs to be wide (in the radial direction).

The assembly according to the present invention comprises a first member18and a second member19, each comprising at least one through hole20-22. The through holes20-22may be directly arranged in the first member18and the second member19, and consequently flanges13,14as shown inFIG. 2are redundant. This has several advantages, one of them being a saving of material. The second member19is made up out of an amount of material that is approximately also present in a single one of the flanges13,14ofFIG. 2. However, the material required for the first flange13inFIG. 2is completely saved. Also, due to the absence of flanges13,14, there is less weight outside the line of travel of forces through the assembly. Moreover, a labour intensive and costly welding operation is prevented.

A taper angle at the bottom of member19and a taper angle at the top of member18allows for a certain amount of ovality in either member18or19to be forced back into a round shape under the force of gravity by pushing member19into member18.

In the shown embodiment, the first member18comprises one through hole20, and the second member comprises two through holes21,22. In the assembly, the through holes20-22of the first18and the second member19together define a channel23. A connector24is axially insertable in said channel23to an end position and consecutively expandable radially relative to said channel23, to connect the first member18and the second member19relative to each other.

The connector24comprises a compacted state (shownFIGS. 9 and 10), wherein the connector24has a size that is freely insertable into and out of the channel23, and a connecting state (e.g. shown inFIGS. 4 and 11) wherein the connector is expanded in the channel23to connect the first18and second member19relative to each other.

The description is this paragraph relates to the orientation shown inFIG. 11, but the skilled person will understand the same principle may also be applied in other orientations, such as transverse or upside down relative toFIG. 11. In the connecting state shown inFIG. 11, the connector24contacts at its lower side with faces41formed at the lower side of the respective through holes21,22of the second member19. The upper side of the connector24contacts a face42that is arranged at the upper side of the through hole20in the first member18. In the expanded state of the connector24, the connector24pushes faces41of the second member18away from face42of the first member18. Consequently, the second member19is pushed downward relative to the first member18, and a clamping contact is formed between a face43defined by the upper side of the first member18, and a face44defined by the second member19. Thus, by expanding the connector24, a pre-tensioned connection between the first18and the second member19can be formed. The faces41,42,43,44can be best seen inFIG. 8. By having sufficient pretension, the load fluctuations going through the connector24are reduced significantly resulting in very low fatigue levels.

The connector24comprises at least one expansion block25, at least one wedge26, and an actuator27configured to displace the wedge26relative to the expansion block25. The wedge26has an inclined surface28facing the at least one expansion block25.

The connector24preferably comprises at least one wedge26that is arranged between two expansion blocks25, and more preferably the connector24comprises two wedges26. In the shown embodiment, two wedges26are arranged between two expansion blocks25. The two wedges26are symmetrically arranged with inclinations of the inclined surface28thereof directed away relative to each other.

The actuator27may be a bolt29that engages in a threaded recess30of the wedge26. Optionally a washer38may be placed between the head of the bolt29and the wedge26. By turning the bolt29, the wedges26may be pulled together over a distance corresponding to the thread of the bolt29. When two wedges26are used, the displacement is divided over both wedges26. The thread may be interpreted as a first transmission and the division over both wedges as a second transmission. Via the inclined surface28, which may be interpreted as a third transmission, the connector24is expanded, i.e. the expansion blocks25are pressed outward relative to each other when the wedges26move towards each other. One of the expansion blocks25engages with the faces41of the second member18, i.e. the lower expansion block25shown inFIG. 11. The other expansion block25, i.e. the upper expansion block25shown inFIG. 11, engages with the face42of the first member18. In this way, if the expansion blocks25are pressed outward relative to each other, the above described pre-tensioned connection between the first18and the second member19can be formed.

The inclined surface28of said wedge26may comprises an inclination with an angle of less than 15°, preferably less than 10°, more preferably less than 8°, and most preferably equal to or less than 6°, relative to a displacement direction of said wedge26. This displacement direction coincides with the longitudinal direction of the bolt29. By providing an inclination with a relatively flat angle, an axial clamping force Fcresults after decomposition thereof in only a very limited radial force component. The relatively small value of the radial force component is typically less than the friction at the contact surface between wedge26and clamping block25, resulting in a self-locking contact between the wedges26and the clamping block25in the connecting state. As a result, the wedges26remain in place even if the bolt29forming the actuator27for originally displacing the wedges26would be loosened or even removed. Although it is preferable that the bolt29remains tightened, this self-locking aspect prevents that the bolt29may experience stress fluctuations during use. In this way, a reliable and fail-safe assembly is provided.

The expansion block25has a surface31of which at least a portion32is a contact surface with the wedge26having an orientation corresponding with the inclined surface28of said wedge26. When the orientation of the contact surface and the inclined surface28are substantially equal, a reliable mating interface is obtained.

If only a portion32of the surface31is a contact surface, the contact surface may remain constant over a displacement range of the wedge32. If the wedge26that is shown on the right side inFIGS. 5-7is moved inward, the contact surface will not further increase once its front edge39passes edge40of portion32.

As can be best seen inFIGS. 3 and 12, the first18and the second member19are overlapping tubular members and the through holes20-22are radially aligned relative to the tubular members to define the channel23that is radially extending. The first18and second member19have respective longitudinal axes33,34that are at least parallel, and preferably coincide (FIG. 3). In the prior art situation shown inFIG. 2, the nut40had to be accessible with tools. However, according to the present invention, an airtight platform37may be provided without preventing access to the connection between the first18and second member19. To the contrary, it is exactly this airtight platform37that may provide a comfortable support for a user to readily place connectors24in respective channels23.

A symmetrical force transmission may be obtained if, according to the shown preferred embodiment, the second member19has a fork-shaped cross section with a main body35and two substantially parallel walls36that each comprises at least one through hole. In this embodiment, the first member18is arranged between the two walls36of the second member19, having the through holes21,22, and said through hole20of the first member18and the through holes21,22of the second member19are positioned to define the channel23. The arrows inFIG. 11indicate how a clamping force Fcis symmetrically distributed.

The channel23preferably has an elongate cross section extending in a longitudinal direction of at least one of said first18and said second member19. Relative to channels having a circular shape, such an elongate cross sectional shape provides a relatively large amount of material between successive channels23if multiple channels23and connectors24are arranged along a circumference of the first18and the second member19.

In a second embodiment of the invention, the wedges26′ are only inclined on one side relative to a displacement direction of said wedges26′, i.e. the upper side inFIG. 13. The other side of each wedge26′, i.e. the lower side inFIG. 13, is substantially parallel to the displacement direction of said wedge26′. Expansion block25′ has two substantially parallel sides, which allows it to be placed in advance of the wedge26′ and other expansion block25of the assembly. Expansion block25′ also better facilitate de-assembly.

A third embodiment of the invention, wherein a single wedge26is applied, is shown inFIG. 14.

A fourth embodiment of the invention is shown inFIG. 15. This embodiment combines a single wedge26according to the embodiment ofFIG. 13with an expansion block25′ that has two substantially parallel sides according to the embodiment ofFIG. 13.

In a (not shown) embodiment, the clamping blocks25may be connected by a flexible member enclosing the space between the clamping blocks25where the wedges26are arranged. In such an enclosed space, lubricant may be added.

According to a fifth embodiment of the invention that is shown inFIG. 16, the second member19is embodied as an assembly rather than a one piece element. The fork-shaped cross section is defined by the assembly of the main body35and the two substantially parallel walls36. The walls36partially extend along, and are connected to, opposite sides of this main body35. The walls36may be defined by a plurality of plates45. The plates45may comprise though holes46to allow a pin47to pass through said plates45and through a corresponding through hole48in the main body35of the second member19. In the shown embodiment, a bolt49and washer50are being used to clamp the plates45that define the side walls36to the main body35. The bolts49are preferably arranged on an inside of the tubular first18and second member19to allow easy access. There is a modest pretension between the main body35and the plates45that are arranged on opposite sides thereof. Upon tightening of the connector24the dominant load transfer path however is through an applied tensile force through the plates45that is transferred into a shear force in the pin47. Connector24, both plates45on the inner and the outer side of the second member19and pin47all form part of the pretension load transfer path. Consequently, very low load fluctuations are felt by these components when an external load is applied at the connection. In a preferred embodiment, each connector24is associated with an inner plate45and one outer plate45. The clamping action of the fifth embodiment is similar to the other embodiments.

Relative to second member19comprising a one piece fork-shaped cross section, an assembly according to the fifth embodiment has several advantages and disadvantages.

A disadvantage of the fifth embodiment is the open structure, formed by the plurality of separate plates45. This may limit the main use of the fifth embodiment to so-called in-air conditions where the construction is not continuously exposed to salt spray, as would be the case in the so-called splash zone. If used in offshore applications, the fifth embodiment is preferably applied well above the splash zone, i.e. well above sea level. However, if a sealing is used in-between the plurality of separate plates45, this fifth embodiment may also find its use at the splash zone or even below. The individual plates45may also be designed so that the plates overlap one another at the interface to adjacent plates including an overlap that seals the interface and prevents water and/or air penetration.

On the other hand, the fifth embodiment also comprises a number of important advantages.

Firstly, it is not required to make a solid ring, which typically requires a forging process that—in the required sizes—may only be applied by a limited number of highly specialized companies. The plates45and pins47according to the fifth embodiment can easily be produced by most metal work shops allowing the essential part of the connection to be produced by a large number of companies.

Secondly, once a solid ring is forged, forming of a groove therein is time intensive and causes a significant amount of steel to be removed in a machining step. The production of plates45, however, has the benefit that no material needs to be removed in between the plates45as is the case with a solid forging that requires machining to remove the groove.

Thirdly, large forged rings are heavy and bulky, resulting in logistic challenges and costs. Plates45and pins47are easy to transport, and—because they may be made by a large number and broader range of companies—transport may be minimized if local metal work shops produce these parts.

Fourthly, the forged and machined ring needs to be welded to the second member19, thereby possibly deforming the face44of said second member19. This deformation may result in so-called waviness and may have a negative effect on the structural integrity of the connection since the resulting gap needs to be closed using the pre-stress applied by the connectors24.

Finally, increased flexibility is obtained if a number of plates45is provided with additional functionality, such as alignment functionality.

In the shown embodiments, the first18and the second member19are members of an offshore construction, more in particular of an offshore wind turbine construction1. Each of the first18and the second member19may be an upright member of a monopile3. It is however explicitly mentioned that the invention is not limited to offshore use. Especially the fifth embodiment as described above is particularly suitable for use in onshore wind turbine applications. Onshore, the combination of the limited diameter of tubulars that can be transported over the road, the ever increasing tower height to catch stronger winds, and growing wind turbines power ratings results in connections between tubulars that are exposed to very high load levels. These load levels may even exceed typical L-flange load levels. In comparison with conventional L-flange connections, the absence of two welds between flanges and tubulars and the absence of the expensive flanges themselves makes the invention, and especially the fifth embodiment, a commercially attractive solution even at lower load levels.

Alternatively, one of the first18and the second member19may be a rotor blade6of a wind turbine1, and the other of the first18and the second member19may be arranged on a hub, and by example said first18or second member19may be arranged on a (not shown) pitch bearing attached to a hub. Such pitch bearing is known in the art and include ball- or roller bearings. The connection between bearing and blade may be established via either an inner or an outer raceway of the bearing as the case may be on a two-raceway bearing.FIG. 1shows this connection C, as well as many other places where a similar assembly may be applied as connection C.

The method of assembling the first18and the second member19that each comprise at least one through hole20-22according to the invention, comprising the steps of:positioning the through holes20-22of the first18and the second member19to define a channel23(step fromFIG. 8toFIG. 9);inserting a connector24into the channel23to an end position (step fromFIG. 9toFIG. 10); andconsecutively expanding said connector24radially relative to said channel23, to thereby connect the first18and second member19relative to each other (step fromFIG. 10toFIG. 11).

Although not shown, the method of assembling may be preceded by the step of positioning at least one of said first18and said second member19by hoisting thereof, wherein a (not shown) hoisting equipment engages at least one of the through holes20-22of said respective first18or second member19. An elongate member, preferably a rod, may be arranged through at least one of the through holes20-22to connect the respective first18or second member19to the hoisting equipment.

The same through holes20-22may also be used for engagement with an installation tool.

Although they show preferred embodiments of the invention, the above described embodiments are intended only to illustrate the invention and not to limit in any way the scope of the invention.FIG. 1shows an offshore wind turbine tower construction, but the assembly according to the invention is not limited to offshore use, nor to wind turbine applications alone.

It is remarked that in the description of the shown embodiments, the lower member is denoted as the first member18, and that the upper member is denoted as the second member19. The skilled person will understand that the lower member could be interpreted as a second member19and the upper member could be interpreted as a first member18within the scope of the invention.

It should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. The scope of the invention is defined solely by the following claims.