Patent Publication Number: US-11377807-B2

Title: Device for levelling an offshore foundation construction

Description:
The present invention relates to the technical field of offshore foundation constructions, in particular offshore foundation constructions intended to support an offshore wind turbine. More specifically, the invention relates to a device for levelling such an offshore foundation construction. 
     Offshore devices such as offshore wind turbines usually rest on an offshore foundation construction including a structure and foundation piles. The structure may include for instance a jacket or a tripod. The offshore foundation construction is arranged on a seabed. More specifically, the offshore foundation construction is secured to the seabed by the foundation piles driven into the seabed. An upper end of the foundation piles is connected to the structure. The offshore foundation construction is then firmly secured to the seabed and the offshore device may keep on operating properly while resisting to aggressive conditions such as a storm, an important stream or waves. 
     Below the structure, conventional offshore foundation constructions sometimes include a mudmat laying horizontally on the seabed. The mudmat aims at distributing the load on a large surface of the seabed. The mudmat can, for instance, consist of a metallic plate. 
     During installation of an offshore foundation construction, it is a thorny problem to level the offshore foundation construction that is to ensure that the orientation of the offshore foundation construction meets accurately with the design specifications. 
     One conventional solution for levelling an offshore foundation construction includes firstly performing installation of the offshore foundation structure, that is setting down the structure on the seabed and driving the foundation piles into the seabed. Secondly, this conventional method includes exerting a load on a part of the structure to level the structure. For instance, a lower corner of the structure may be pulled up. By doing so, the orientation and/or the position of the structure is modified. 
     Although such a solution allows levelling an offshore foundation structure, it is not fully satisfactory. Firstly, the effort exerted on the structure involves a risk of deforming and weakening the structure. Secondly, the effort to be exerted on the structure and foundation piles is extremely important due to the friction between the piles and the structure. Thirdly, an important effort is required for moving the offshore foundation construction together with the foundation piles. Those efforts may even induce a detrimental bending of the foundation piles. 
     One other conventional solution includes setting down a template structure that reproduces the bulk of the offshore foundation on the seabed, levelling the template structure, confirming the position of the piling sites and driving piles in said sites. Then, the conventional method includes removing the template structure and installing the offshore foundation structure. 
     This solution is also not fully satisfactory because the use and manipulations of a heavy template structure are both time consuming and costly. 
     The invention aims at overcoming the above-mentioned drawbacks. More specifically, the invention aims at allowing levelling an offshore foundation construction while decreasing the risk of deforming or weakening the structure as with the first conventional solution and also removes the need for the use of a template as with the other conventional solution. 
     According to a first aspect of the invention, it is proposed a device for levelling an offshore foundation construction, including a cylinder equipped with a fastening means for removably fastening the cylinder to a part of the offshore foundation construction, a rod mobile in axial translation with respect to the cylinder, the rod including a pushing end so configured to push against a mudmat. 
     The mudmat may be part of the offshore foundation construction. 
     Such a device allows levelling the offshore foundation construction prior to insertion of the foundation piles, preventing the structure to revert back into its original position and avoiding the use of a template structure. The risk of deforming or weakening the structure and/or the foundation piles is avoided. 
     According to an embodiment, the pushing end has a spherical shape, the curvature radius of the spherical shape of the pushing end being preferably within a range 450 mm to 1500 mm, more preferably within a range 1000 mm to 1500 mm. 
     Such a design of the pushing end, especially with a curvature radius within this range, is adapted to cooperate with a mudmat of an offshore foundation construction, in particular intended to support an offshore wind turbine. 
     According to another embodiment, the fastening means is configured for fastening the cylinder to a bearing part of the offshore foundation construction. 
     Preferably, the bearing part is a sleeve, the sleeve being part of a structure or of an adapter of the offshore foundation construction. 
     Advantageously, the sleeve is a cylinder having a circular radial cross section. 
     According to another embodiment, the fastening means includes at least two clamping chucks spread over the outer circumference of the cylinder. 
     Clamping chucks are particularly well adapted in the device according to the invention because it allows fastening remotely and firmly in a subsea environment. 
     According to an embodiment, the rod includes a cylindrical part having a circular radial cross section, the radius of the circular radial cross section being preferably within a range 450 mm to 1500 mm. 
     The so-designed rod is especially adapted for a device for levelling an offshore foundation construction intended to support an offshore wind turbine. 
     According to an embodiment, the device further includes a measurement system for measuring a displacement of the rod with respect to the cylinder, the measurement system including a first measurement unit arranged within the rod and/or a second measurement unit arranged within the cylinder. 
     The measurement system allows monitoring the levelling operation of the offshore foundation construction. If the measurement system includes both first and second measurement units, it is possible to perform a redundant measuring so as to increase the reliability of the levelling operation. 
     In another embodiment, the cylinder includes an upper frontal surface, the device including a connection part axially upwardly protruding from the upper frontal surface, the connection part being intended to accommodate a connection line, the connection part being able to be caught in order to remove the device from the offshore foundation construction. 
     In a more specific embodiment, the connection part includes a lower portion and an upper portion, the lower portion being cylindrical, the upper portion being frustoconical, the connection part including a bore extending inside the lower portion and the upper portion, the lower end of the upper portion having a larger radial cross-section than the radial cross-section of the lower portion. 
     Such a connection part is particularly well adapted for allowing a control line such as a guiding tool to be inserted within the bore. Furthermore, the connection part may be easily caught up by a catching apparatus so as to remove the device from the offshore foundation construction after the levelling operation. 
     In a possible embodiment, the mudmat may be secured to the rod. This embodiment enables handling of the mudmat and device together during positioning. 
     In another embodiment, the device includes a mudmat at least partially removably secured to the rod. This embodiment enables handling of the mudmat and device together during positioning while allowing to leave the mudmat in situ in case of need. 
     In yet another embodiment, the device includes a mudmat at least partially removably secured to the offshore foundation structure. This embodiment eases handling and positioning of the mudmat while allowing the levelling operation once positioned. 
     In a further embodiment, the device includes a mudmat made of several parts. This embodiment may ease installation, positioning or removal of the mudmat in some configurations of the offshore foundation construction. 
     According to another aspect of the invention, it is proposed an adapter for an offshore foundation construction including a device as set forth above. 
     In a specific embodiment, the adapter includes a central sleeve and a peripheral sleeve for insertion of a pile of the offshore foundation construction, the device being inserted within the central sleeve. 
     According to a further aspect of the invention, it is proposed an offshore foundation construction including a structure, a mudmat and a device as set forth above and/or an adapter as set forth above. 
     According to a further aspect of the invention, it is proposed a method of levelling an offshore foundation construction, preferably an offshore foundation construction intended to support an offshore wind turbine, including fastening a device as set forth above to a part of the offshore foundation construction, and actuating a motion of axial translation of the rod with respect to the cylinder so as to push against a mudmat of the offshore foundation construction. 
     It may also be foreseen that the steps of fastening and actuating are implemented prior to a step of inserting a first pile of the offshore foundation construction. 
    
    
     
       The present invention and its advantages will be better understood by studying the detailed description of a specific embodiment given by way of nonlimiting examples and illustrated by the appended drawings on which: 
         FIG. 1  is a side view of an offshore foundation construction according to one aspect of the invention, 
         FIG. 2  is a isometric view of an adapter of the offshore foundation construction of  FIG. 1 , 
         FIG. 3  is a isometric view of a first device embodiment for levelling the offshore foundation construction of  FIG. 1 , 
         FIG. 4  is a side view of the device of  FIG. 3  in a first configuration, and 
         FIG. 5  is a side view of the device of  FIG. 3  in a second configuration. 
     
    
    
     With reference to  FIG. 1 , it is schematically depicted an offshore foundation construction  2 . The offshore foundation construction  2  aims at resting on a seabed (not depicted) and at supporting an offshore device (not depicted), in particular an offshore wind turbine. Nonetheless, the offshore foundation construction  2  may be used for supporting another kind of offshore device, such as an offshore hydrocarbon production platform. 
     It is defined an orthonormal direct vector base  4  attached to the offshore foundation construction  2 . The base  4  consists of a vector {right arrow over (x)}, a vector {right arrow over (y)} and a vector {right arrow over (z)}. 
     In the present application, terms “low”, “down”, “up”, “horizontal” and “vertical” will be understood as referring relative to the base  4  when the offshore foundation construction  2  is normally installed on a horizontal seabed, that is assuming that the vector {right arrow over (z)} is vertically upwardly directed. 
     As well, the word “cylindrical” will be understood according to its common definition, being namely that a cylindrical surface is a surface consisting of all the points on all the lines which are parallel to a given line and which pass through a fixed plane curve in a plane not parallel to the given line. 
     The offshore foundation construction  2  includes a structure  6 . The structure  6  includes four main legs  8 , only two legs  8  being visible on the side view of  FIG. 1 . The structure  6  also includes a plurality of braces  10 . The braces  10  connect mechanically a leg  8  with another leg  8 . On the side view of  FIG. 1 , only four braces  10  are visible. 
     In the depicted embodiment, the structure  6  is a jacket. However, it would be possible without departing from the scope of the invention to have a structure having a different design, being for instance a tripod. 
     The offshore foundation construction  2  includes, for each main leg  8 , an adapter  12 . That is, in the embodiment of  FIG. 1 , the offshore foundation construction  2  includes four adapters  12 , only two of them being visible on the side view of  FIG. 1 . For each main leg  8 , an adapter  12  is attached to a lower end of the main leg  8 . In the depicted embodiment, the adapters  12  are welded to the legs  8  before that the offshore foundation construction  2  is launched in the sea. 
     As visible on  FIG. 1 , each adapter  12  is associated with a mudmat  14 . For each adapter  12 , the mudmat  14  is an independent part and is arranged to rest on top of the seabed. The adapter  12  is arranged above the mudmat  14 . The mudmat  14  may be made of a material including concrete and/or steel and/or composites. 
     With reference to  FIG. 2 , the adapter  12  includes a central sleeve  16  and five peripheral sleeves  18 . In the embodiment illustrated in  FIG. 2 , the sleeves  16  and  18  are cylindrical about the direction of the vector {right arrow over (z)}. The sleeves  16  and  18  may optionally be tilted with respect to the vector z. Nonetheless, possible variations of the invention may comprise a different number of peripheral sleeves  18  and/or a different geometrical arrangement of peripheral sleeves  18 . The sleeves  18  are all located on a circle about the axis of the sleeve  16 . The sleeve  16  and the sleeves  18  have a circular radial cross-section. The diameter d 18  of the radial cross section is substantially the same for all the sleeves  18 . The diameter d 16  of the radial cross section of the sleeve  16  is approximately twice the diameter d 18 :
 
1,0× d   18   &lt;d   16 ≤3,0× d   18  
 
     Each adapter  12  includes a metallic subframe  20 . The metallic subframe  20  includes a plurality of metallic hollow sections (not referenced) and metallic plates (not referenced). For each adapter  12 , the metallic subframe  20  aims at connecting the sleeve  16 , the sleeves  18  and a joining portion for attaching the adapter  12  with a lower end of the main leg  8 . 
     As visible on  FIG. 2 , each sleeve  18  includes an upper portion  22 . For each sleeve  18 , the portion  22  is frustoconical about the axis of the peripheral sleeve  18 . More specifically, the portion  22  vertically extends between a lower circular end with a diameter d 22d  and an upper circular end with a diameter d 22u . The diameter d 22d  equals the diameter d 18  and the diameter d 22u  is larger than the diameter d 22d :
 
 d   22d   =d   18  
 
2× d   22d   &lt;d   22u ≤3× d   22d  
 
     Preferably, the angle of the frustoconical shape of the portion  22  is within a range 40° to 55°. The frustoconical shape of the portion  22  helps inserting a foundation pile in a sleeve  18  in order to secure the offshore foundation construction  2  to the seabed. The central sleeve  16  is located above the mudmat  14 . The peripheral sleeves  18  are offset with respect to the mudmat  14 . 
     With reference to  FIG. 3 , the adapter  12  is depicted in partial cross-section relative to the plane III-III. The plane III-III is perpendicular to the vector {right arrow over (y)} and includes the axis of revolution of the sleeve  16 . As may be seen on  FIG. 3 , the sleeve  16  contains a device  24 . Unlike the adapter  12 , the device  24  is not represented in cross-section on  FIG. 3 . The device  24  is also depicted on the side view of  FIG. 4 . The device  24  aims at allowing to level the offshore foundation construction  2 . 
     The device  24  includes a cylinder  25 . The cylinder  25  forms substantially a cylinder of revolution about an axis  26 . Unless contrary indication, the words “axial”, “axially”, “radial”, “radially” will be understood as referring relative to the axis  26 . The axis  26  is parallel to the vector {right arrow over (z)} and matches with the axis of revolution of the sleeve  16 . 
     The cylinder  25  includes a central portion  28 . The portion  28  is cylindrical with a circular radial cross-section about the axis  26 . The diameter d 28  of the radial cross-section of the portion  28  is slightly smaller than the diameter d 16 . 
     The cylinder  25  includes a lower portion  30 . The portion  30  extends axially between the portion  28  and a lower frontal surface  32 . The portion  30  is frustoconical about the axis  26 . More specifically, the portion  30  is axially, upwardly delimited by an upper circular end having a diameter d 30 . As the opposite end, the surface  32  forms a circle about the axis  26  having a diameter d 32 . The diameter d 30  is generally larger than the diameter d 32  or equal:
 
 d   30 ×0,75&lt; d   32   ≤d   30  
 
     The device  24  includes an upper cap  34 . The cap  34  includes a plurality of vertical walls  36 , for instance six vertical walls  36 . The walls  36  are attached by their lower end to the portion  28 . The walls  36  are attached by their upper end to a horizontal upper wall  38 . The wall  38  is axially upwardly delimited by an upper frontal surface  40 . In view of the foregoing, the cylinder  25  extends axially between the frontal surfaces  32  and  40 . 
     With reference to  FIGS. 3 and 4 , the device  24  includes a connection part  42 . The part  42  includes a lower portion  44 , a central portion  45  and an upper portion  46 . The portions  44  and  45  are cylindrical with a circular radial cross-section about the axis  26 . The diameter d 44  of the radial cross-section of the portion  44  is smaller than the diameter d 45  of the radial cross-section of the portion  45 . 
     The portion  46  is frustoconical about the axis  26 . More specifically, the portion  46  extends axially between an upper circular end having a diameter d 46u  and a lower circular end having a diameter d 46a . The diameter d 46u  is smaller than the diameter d 46d  and the diameter d 46d  equals the diameter d 45 . 
     The part  42  extends axially, upwardly from the surface  40 . More specifically, the connection part  42  is mechanically secured to the wall  38  by means of a collar  48 . By virtue of this arrangement, the part  42  forms a hook that can be caught by a catching apparatus (not depicted). 
     As may be seen on  FIG. 3 , the part  42  includes a through bore  50 . The bore  50  is cylindrical with a circular radial cross-section about the axis  26 . The diameter d 50  of the radial cross-section of the bore  50  is smaller than the diameters d 44  and d 46u . 
     Axially, the bore  50  extends on the whole axial length of the part  42 . In other words, the bore  50  extends axially through the portions  44 ,  45  and  46 . The bore  50  can accommodate at least one connection line (not depicted). The connection lines are intended to connect the device with various devices so as to provide a fluid connection, electrical connection, data connection, etc. For instance, the connection lines accommodated in the bore  50  may include guiding tools, fluid hoses, control lines, and data transfer cables. Typically, the bore  50  may be used for accommodating an umbilical with its connector. 
     With reference to  FIG. 4 , the device  24  includes a hydraulics system  52 . The hydraulics system  52  aims at generating a hydraulic force by means of a hydraulic fluid which may be, for instance, oil or water. 
     With reference to  FIG. 3 , the hydraulics system  52  includes a hot stab  54 . The hot stab  54  allows connecting a hydraulic duct (not depicted) to the hydraulics system  52 . Using a hot stab  54  is advantageous because it renders the hydraulic fluid connection reliable in a submarine environment. 
     With reference to  FIG. 4 , the device  24  includes a rod  56 . Only a portion of the rod  56  is visible on  FIG. 4 , a significant part of the rod  56  being hidden by the cylinder  25 . On  FIG. 5 , the rod  56  has been displaced downwards with reference to the cylinder  25 . The rod  56  includes a cylindrical part  58  and a hemispheric part  60 . The part  58  is proximal with respect to the cylinder  25  whereas the part  60  is distal with respect to the cylinder  25 . The part  58  is cylindrical with a radial circular cross-section about the axis  26 . The radius d 58  of the radial cross-section of the part  58  is within a range 450 mm to 1500 mm. The part  60  is connected by an upper flat surface to a lower frontal surface of the part  58 . The radius r 60  of the hemispheric part  60  is within a range 450 mm to 1500 mm, preferably a range 1000 mm to 1500 mm. 
     The rod  56  is mobile in axial translation about the direction of the vector {right arrow over (z)} with respect to the cylinder  25 . The translation motion of the rod  56  is actuated by a hydraulic force generated by the hydraulics system  52 . More specifically, the rod  56  is driven axially downwards with respect to the cylinder  25  when a hydraulic force is generated by the hydraulics system  52  into the rod  56  (see  FIG. 5 ). By doing so, the cylinder  25  and the rod  56  form together a piston and the hemispheric part  60  forms a pushing end so arranged to push against the mudmat  14  associated with the adapter  12  containing the device  24 . Instead of the hemispheric part  60 , the distal part of the rod may include a universal joint with a first side of the joint connecting the lower frontal surface of the part  58  and a second side of the joint providing a flat foot arranged so as to rest on the mudmat  14 . 
     The device  24  includes a first measurement unit  62  and a second measurement unit  64 . The units  62  and  64  have a communication link with a control unit (not depicted) of the device  24 . The units  62  and  64  are able to measure the relative displacement of the rod  56  with respect to the cylinder  25 . The unit  62  is arranged inside the rod  56 . The unit  64  is arranged within the cylinder  25 . 
     With reference to  FIGS. 3 to 5 , the device  24  includes eight clamping chucks  66  spread about the axis  26  on the outer circumference of the portion  28 . More specifically, the clamping chucks  66  are able to move, with respect to the cylinder  25 , in radial translation. The radial translation of the clamping chucks  66  is actuated by a hydraulic force generated by the hydraulics system  52 . More specifically, the clamping chucks are radially, outwardly driven with respect to the cylinder when a hydraulic force is generated by the hydraulics system  52  into the clamping chucks  66 . 
     By virtue of this arrangement, the clamping chucks  66  are able to exert a normal effort on the inner cylindrical surface of the sleeve  16 . When such a normal effort is exerted, the clamping chucks  66  grip the sleeve  16  so as to form fastening means of the device  24  to the adapter  12 . 
     In the depicted embodiment, the clamping chucks  66  are intended to fasten the cylinder  25  to the adapter  12 . Nonetheless, it may be foreseen a different fastening of the cylinder  25  to the offshore foundation construction  2  without departing from the scope of the invention. For instance, it may be provided a fastening means of the cylinder  25  to a steel beam of the structure  6 . 
     In order to level the offshore foundation construction  2 , the adapters  12  are firstly welded to the legs  8 . Such a welding operation is for instance implemented on dry dock. 
     Secondly, the devices  24  are inserted in the central sleeves  16  of the adapters  12 , respectively. More specifically, in the described embodiment, at least three devices  24  are inserted on three out of the four sleeves  16 . It may however be foreseen that a different number of devices  24  may be used, for example for safety reasons. The insertion of the devices  24  is facilitated by the frustoconical shape of the portion  30 . Then, a hydraulic force is generated by the hydraulics system  52  into the clamping chucks  66 . At the end of this step, the devices  24  are firmly attached to the adapters  12 . 
     Once the devices  24  are fastened, the offshore foundation construction  2 , including the structure  6 , the four adapters  12  and the three devices  24 , is launched in the water. Implementing the step of inserting the devices  24  prior to the step of launching the offshore foundation construction is advantageous since it reduces the number of steps to be implemented during an installation process of the offshore foundation construction  2 . However, the steps of inserting and fastening the devices  24  and the step of launching the offshore foundation construction  2  may be inverted without departing from the scope of the invention. 
     Then, a control unit collects the information of the orientation of the offshore foundation construction  2 . The control unit emits a corresponding correction signal. The correction signal includes a target signal for the displacement of the rod  56  of each device  24 . 
     For each device  24 , a hydraulic force is generated by the hydraulics system  52  into the rod  56 . By doing so, the pushing end of the rod  56  pushes on the mudmat  14  facing the device  24  as depicted on  FIG. 5 . The adapter  12  associated with the device  24  is moved vertically so that the orientation of the structure  6  is modified. 
     During the step of generating a hydraulic force into the rod  56 , the displacement can be monitored by the measurement system formed by the units  62  and  64 . This allows the control unit to monitor the individual vertical displacement of each adapter  12  so as to monitor accurately the levelling of the offshore foundation construction  2 . 
     When the levelling of the offshore foundation construction  2  is complete, foundation piles (not depicted) are inserted within the sleeves  18 . The insertion of the foundation piles is facilitated by the frustoconical shape of the portions  22 . The foundation piles are driven into the seabed by a hammering process or by any other suitable driving process. Once the foundation piles are inserted into the seabed, the hydraulics system  52  stops generating the hydraulic force into the rod  56 . 
     Then, the hydraulic force exerted by the hydraulics system  52  into the clamping chucks  66  is relaxed. The devices  24  are caught up by a catching apparatus (not depicted) cooperating with the hook formed by the connection part  42 . The devices  24  are then removed from the offshore foundation construction  2  and may be used for levelling another offshore foundation construction. 
     In view of the foregoing, the invention allows to level the offshore foundation construction  2  while decreasing the risk of deforming or weakening the structure  6  and/or the foundation piles. Furthermore, the levelling efforts are importantly reduced because the foundation piles are inserted in the seabed after the process of levelling. The device for levelling is not cumbersome and the fact that it can be installed prior to immerse the offshore foundation construction decreases the number of steps of the installation process of the offshore foundation construction.