Construction method for floating structures

Abstract

This invention provides a construction method for spar-type floating structures that is less susceptible to adverse weather and oceanographic conditions. [Solution] A method for constructing a floating structure comprising a ballast section, a cylindrical spar section, and a wind turbine includes a ballast filling step in which ballast is filled into the internal space of the ballast section in a first body of water having a depth deeper than a first draft which is a predetermined draft in the ballast section, and shallower than the sum of the height of the ballast section and the height of the spar section when the spar section is connected to the ballast section, thereby obtaining the first draft.

Description

Technical Field

[0001] The present invention mainly relates to a construction method for a spar-type floating structure of an offshore wind power generation facility.

Background Art

[0002] Wind power generation that generates electricity using natural wind has been attracting attention from the perspective of effective utilization of the environment and natural energy. In addition, numerous proposals have been made for offshore wind power generation facilities or floating structures in which wind power generation facilities are installed on water (mainly offshore).

[0003] Patent Document 1 describes a construction method for a floating offshore wind power generation facility, which is a construction method of installing a deck, a tower, and a nacelle on a spar-type floating structure (a floating structure including a ballast portion) that is grounded in an upright state on the seabed (see FIG. 12 to FIG. 15 of Patent Document 1).

[0004] The floating structure used in Patent Document 1 (the floating body 2 illustrated in FIG. 2 of Patent Document 1) is composed of a bottomed cylindrical ballast portion 10, a lower concrete floating structure portion 2A continuously provided on the upper surface of the ballast portion 10, and an upper steel floating structure portion 2B continuously provided on the upper side of the lower concrete floating structure portion 2A.

[0005] As can be seen from paragraphs 0022 to 0031 and Figure 7 of Patent Document 1, the floating body 2, which consists of a bottomed cylindrical ballast section 10, a lower concrete floating structure section 2A, and an upper steel floating structure section 2B, is manufactured as a single structure in a manufacturing yard and then towed to the erection site (see Figure 6 and paragraph 0031 of Patent Document 1), where it is erected (see Figure 7 and paragraph 0033 of Patent Document 1). The erection site has a water depth such that the bottom surface of the floating body 2 does not touch the seabed when the floating body 2 is erected, a predetermined amount of ballast is added, and a predetermined draft is secured (see paragraph 0031 of Patent Document 1). The draft of the floating body 2 varies depending on the scale of the power generation equipment attached to the floating body 2, but Patent Document 1 exemplifies 60m or more (2MW class power generation equipment, see paragraph 0020) or 70m (see paragraph 0005).

[0006] Subsequently, a fluid mixture of ballast material and water is injected into the floating structure, which is standing upright above the seabed, using a material ship loaded with ballast material and a dredger equipped with a large pump (see Figure 8 and paragraph 0034 of Patent Document 1), thereby ensuring a predetermined draft for the floating structure 2 and causing it to stand upright while floating above the seabed.

[0007] The floating body 2, which is upright and suspended above the seabed, is towed to a designated bottoming location in a shallower area than the offshore installation site, and settles on the bottom by being injected with ballast water (see Figure 10 and paragraph 0036 of Patent Document 1). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2012-201218 [Overview of the project] [Problems that the invention aims to solve]

[0009] Thus, in the construction method of Patent Document 1, a floating body (floating body 2 in Patent Document 1), which is manufactured as a single structure consisting of a ballast section, a lower concrete floating body structure, and an upper steel floating body structure, is erected at a designated erection site in the ocean with a water depth of 60 meters or more, and then ballast material is placed in the ballast section of the floating body. Sea areas that meet the condition of a water depth of 60 meters or more are often located offshore far from the shore and are directly affected when weather and sea conditions are unfavorable. Therefore, in the construction method of Patent Document 1, it is necessary to determine the weather and sea conditions of the sea area including the erection site, and then select a time when the weather and sea conditions are favorable to place ballast material in the ballast section of the floating body and erect the floating body. Consequently, in the construction method of Patent Document 1, the process of placing ballast material in the ballast section may be a cause of delays in the construction period due to its susceptibility to adverse weather and sea conditions.

[0010] One aspect of the present invention has been made in view of the above-mentioned problems, and its object is to provide a construction method for a spar-type floating structure that is less susceptible to adverse weather and ocean conditions compared to the construction method described in Patent Document 1. [Means for solving the problem]

[0011] To solve the aforementioned problems, a method for constructing a floating structure according to one aspect of the present invention is a method for constructing a floating structure comprising a bottomed cylindrical ballast section having an opening at its upper end, a cylindrical spar section connected to the upper end, and a wind turbine connected to the spar section, comprising a placement step of placing the ballast section in a floating state, with the spar section unconnected and before the predetermined amount of ballast is placed inside, in a first body of water having a depth deeper than a first draft which is a predetermined draft of the ballast section in a state where the spar section is unconnected and a predetermined amount of ballast has been placed inside, and shallower than the sum of the height of the ballast section and the height of the spar section in a state where the spar section is connected to the ballast section, and before the predetermined amount of ballast is placed inside; and a ballast placement step of obtaining the first draft by placing the predetermined amount of ballast into the internal space of the ballast section, which is floating in the first body of water as a result of the placement step.

[0012] According to the above configuration, compared to the construction method described in Patent Document 1, ballast can be placed in the internal space of the ballast section, which is in a standalone state with the spar section and wind turbine not connected, in a first body of water that is shallower in depth. Therefore, the construction method according to one aspect of the present invention allows ballast to be placed in the ballast section in a first body of water that is closer to the quay and set in a calm sea area with calm weather and ocean conditions, compared to the standing location in the construction method described in Patent Document 1. Accordingly, the construction method according to one aspect of the present invention is less susceptible to adverse weather and ocean conditions and can shorten the construction period for building the floating structure, compared to the standing location in the construction method described in Patent Document 1.

[0013] Furthermore, according to the above configuration, ballast can be placed into the internal space of the ballast section, which is in a standalone state with no connected spar sections. Therefore, the construction method according to one aspect of the present invention does not require lifting the ballast to a high position, as described in Patent Document 1, and as a secondary effect, it is possible to improve the energy efficiency when placing the ballast.

[0014] To solve the aforementioned problems, a method for constructing a floating structure according to another aspect of the present invention is a method for constructing a floating structure comprising a bottomed cylindrical ballast section having an opening at its upper end, a cylindrical spar section connected to the upper end, and a wind turbine connected to the spar section, comprising: a placement step of placing the ballast section, in a state where the spar section is not connected and ballast has been placed in its internal space, on a part of the bottom of a tank; and a floating step of, after the placement step, pouring water into the tank to form a first water area and floating the ballast section in the first water area, wherein in the floating step, the water depth of the first water area is set to be deeper than a first draft, which is a predetermined draft of the ballast section in a state where a predetermined amount of ballast has been placed in its internal space, and shallower than the sum of the height of the ballast section and the height of the spar section in a state where the spar section is connected to the ballast section, so that the ballast section obtains the first draft in the first water area.

[0015] According to the above configuration, compared to the construction method described in Patent Document 1, the ballast can be placed into the internal space of the ballast section, which is a standalone unit with the spar section and wind turbine not connected, in a calm area such as a tank (a dock or yard, described later). Therefore, the construction method according to one aspect of the present invention is less susceptible to adverse weather and sea conditions compared to the construction location described in Patent Document 1, and the construction period for constructing the floating structure can be shortened.

[0016] Furthermore, according to the above configuration, ballast can be placed into the internal space of the ballast section, which is in a standalone state with no connected spar sections. Therefore, the construction method according to one aspect of the present invention does not require lifting the ballast to a high position, as described in Patent Document 1, and as a secondary effect, it is possible to improve the energy efficiency when placing the ballast.

[0017] Furthermore, in the construction method for a floating structure according to one aspect of the present invention, the first water area may be located within a harbor or in a sea area where the wave height is 1.5 m or less.

[0018] According to the above configuration, ballast can be placed in the ballast section in a first water area located within a harbor or in a sea area where the wave height is 1.5m or less. Therefore, the construction method according to one aspect of the present invention is less susceptible to adverse weather and sea conditions compared to the construction method described in Patent Document 1.

[0019] Furthermore, in the construction method for a floating structure according to one aspect of the present invention, the first water area may be located in a dock.

[0020] According to the above configuration, ballast can be placed in the ballast section in the first water area provided in the dock. Therefore, the construction method according to one aspect of the present invention is less susceptible to adverse weather and ocean conditions compared to the construction method described in Patent Document 1.

[0021] Furthermore, according to the above configuration, ballast can be placed into the internal space of the ballast section in the dock. Therefore, the construction method according to one aspect of the present invention has the secondary effect of being able to place ballast in a more stable environment compared to the construction method described in Patent Document 1.

[0022] Furthermore, a method for constructing a floating structure according to one aspect of the present invention may further include, in the above configuration, a first towing step of towing the ballast section, which has obtained the first draft in the first water area, into a second water area having a depth deeper than the first water area and shallower than the sum of the height of the ballast section and the height of the spar section; a sinking step of sinking the ballast section to the bottom of the second water area; and a connecting step of connecting the spar section to the ballast section sunk to the bottom of the water area while raising it to obtain a connecting structure.

[0023] In recent years, power generation facilities (that is, wind turbines) attached to floating offshore wind power generation facilities have been increasingly high-output and large-sized, and along with this enlargement, the predetermined draft and total length of the floating structure have also been increased in length. On the other hand, it is difficult to increase the scale of the dock or yard (especially the existing dock or yard) of the manufacturing plant that manufactures the floating structure. According to the above configuration, the ballast section and the spar section can be separately manufactured in the dock, and the ballast section and the spar section can be connected in the second water area, so that when the floating structure is manufactured in the existing dock or yard, it is easy to cope with the increase in length.

[0024] Further, in the construction method for a floating structure according to one aspect of the present invention, in the above configuration, the method may include: a wind turbine installation step of installing the wind turbine on the upper portion of the spar section of the connection structure to obtain the floating structure; a floating step of causing the floating structure obtained by the wind turbine installation step to float from the water bottom; and a second towing step of towing the floating structure floated by the floating step to a third water area having a depth deeper than that of the second water area.

[0025] According to the above configuration, the wind turbine can be installed on the upper portion of the spar section that stands upright with the ballast section grounded on the seabed. The spar section that stands upright with the ballast section grounded in this way is less susceptible to the influence of weather conditions and sea conditions compared to a spar section that stands upright while floating above the seabed. Therefore, the present construction method can suppress relative shaking between the spar section and the wind turbine compared to the case where the ballast section and the spar section are floating above the seabed, so that the construction period for constructing the floating structure can be further reduced. Advantageous Effects of Invention

[0026] According to one aspect of the present invention, in a construction method for a spar-type floating structure, it is possible to provide a construction method that is less susceptible to the adverse effects of weather conditions and sea conditions compared to the construction method described in Patent Document 1. Brief Description of Drawings

[0027] [Figure 1]This is an external view of a floating structure constructed by a construction method according to one aspect of the present invention. [Figure 2] This diagram shows the configuration of the lower equipment of the floating structure shown in Figure 1. [Figure 3] This is a diagram illustrating the flow of a construction method according to one embodiment of the present invention. [Figure 4] This diagram illustrates the flow of the placement process shown in Figure 3. [Figure 5] This figure schematically illustrates a part of a construction method according to one embodiment of the present invention. [Figure 6] This diagram schematically shows a part of the process of a construction method according to one embodiment of the present invention. [Figure 7] This diagram schematically shows a part of the process of a construction method according to one embodiment of the present invention. [Figure 8] This figure illustrates a specific example of a flow chart of a construction method according to one embodiment of the present invention. [Figure 9] This diagram schematically shows a part of the process of a construction method according to one embodiment of the present invention. [Figure 10] This figure schematically illustrates a part of a construction method according to one embodiment of the present invention. [Figure 11] This diagram schematically shows a connection step, which is part of a construction method according to one embodiment of the present invention. [Figure 12] This figure schematically shows one modified example of the connection process shown in Figure 11. [Figure 13] This figure schematically shows one modified example of the connection process shown in Figure 11. [Figure 14] This is a partial cross-sectional view illustrating a connection method in a connection step, which is part of a construction method according to one aspect of the present invention. [Figure 15] This figure schematically illustrates a part of a construction method according to one embodiment of the present invention. [Figure 16] This figure schematically illustrates a part of a construction method according to one embodiment of the present invention. [Figure 17] This is a diagram illustrating the flow of a construction method according to another embodiment of the present invention. [Figure 18] This diagram schematically shows a part of the process in the flow shown in Figure 17. [Modes for carrying out the invention]

[0028] [Embodiment 1] <Floating structure> The following describes a floating structure constructed by a construction method according to one embodiment of the present invention. Figure 1 is a diagram illustrating the floating structure and is a front view of the floating state.

[0029] As shown in Figure 1, the floating structure 1 is a floating type that floats on the water, and is a so-called spar-type floating structure. The floating structure 1 includes a lower structure 2 configured to float on water, and an upper structure 5 positioned above the lower structure 2 and located above the water (in the air). The draft of the floating structure 1 (L1 in Figure 1) is, for example, 100m or more. This draft L1 is a second draft, which is a predetermined draft of the floating structure 1.

[0030] <Superstructure> In this embodiment, the superstructure 5 is a wind turbine 51. Hereafter, it will simply be referred to as the wind turbine 51.

[0031] The wind turbine 51 is a wind power generation device. The wind turbine 51 has, for example, a support column 52, a nacelle 53, and blades 54. The support column 52 is erected on top of the substructure 2 and supports the nacelle 53 and blades 54. The nacelle 53 has a generator (not shown) inside which generates electricity through the rotation of the blades 54. The blades 54 are driven to rotate by wind power.

[0032] In this embodiment, a wind turbine 51 is shown as an example, but the superstructure placed on top of the lower structure 2 is not limited to a wind turbine 51 (wind power generation device), but may also be a wind condition observation device such as a wind vane or anemometer, a solar power generation device, a lighting device, a wireless communication device, etc.

[0033] <Substructure> The substructure 2 will be explained using Figure 2. The substructure 2 consists of two parts: a ballast section 3 and a spar section 4, which are connected together, and the connection is made underwater, as will be described later.

[0034] The ballast section 3 is the bottom structure of the lower structure 2 of the spar-type floating structure 1. The ballast section 3 is bottomed cylindrical in shape and can accommodate ballast in its internal space. The ballast section 3 has an opening at its upper end, which is located on the side connected to the spar section 4, through which ballast can be poured into its internal space. The ballast section 3 surrounds its internal space with a bottom and side walls rising from the bottom, with the side opposite the bottom being the upper end, and an opening provided in a part of the upper end. The periphery of the opening at the upper end includes the surface facing the spar section 4.

[0035] In this embodiment, the ballast section 3 has a rectangular box-like three-dimensional shape in plan view, but it is not limited to this. Also, in this embodiment, the outer diameter of the ballast section 3 is shown to be larger than the outer diameter of the spur section 4, but it is not limited to this, and the outer diameters of the ballast section 3 and the spur section 4 may be equal.

[0036] Here, the ballast section 3 and the spar section 4 are separated by a partition wall provided at a predetermined location inside the spar section 4, which separates the internal space of the ballast section 3 from the majority of the space inside the spar section 4. Ballast is placed in the ballast section 3. Meanwhile, water (seawater) is placed in the space of the spar section 4. Any well-known ballast material can be used for the ballast.

[0037] The ballast section 3 may be made of steel or concrete, for example. However, it is not limited to these. The ballast section 3 may have a volume of 5,000 to 10,000 m³, for example. 3 It has an internal space into which ballast can be placed. The ballast section 3 has a weight of 5,000 to 10,000 tons in one example when ballast is not placed in the internal space.

[0038] The spar section 4 is the upper structure in the substructure 2. The spar section 4 includes a leg section 41 connected to the upper end of the ballast section 3, and a cylindrical main body section 42 having a hollow section erected on the leg section 41.

[0039] The leg portion 41 is a lid-like structure that closes the aforementioned opening in the ballast portion 3. The leg portion 41 may have a recess that allows it to communicate with the internal space of the ballast portion 3 by connecting to the ballast portion 3 as described later. A rubber gasket, described later, is attached to the lower periphery of the leg portion 41 that surrounds the recess. A partition wall is present between the recess of the leg portion 41 and the cylindrical portion of the cylindrical main body portion 42, separating the two spaces. However, the partition wall is provided with a hole for inserting a drain pipe, described later.

[0040] The support column 52 of the wind turbine 51, as mentioned above, is connected to the upper part of the main body 42. For example, the main body 42 has a configuration in which the outer diameter is smaller on the side further from the leg 41 than on the side closer to the leg 41.

[0041] The spur section 4 is configured as an integrated structure of a leg section 41 and a main body section 42. However, it is not limited to this configuration, and the leg section 41 and the main body section 42 may each be separate parts connected together, or in another configuration, the main body section 42 may be composed of multiple cylindrical separate parts connected together.

[0042] Furthermore, if the main body 42 is formed by connecting multiple cylindrical segments, for example, the operation of connecting the segments may be carried out at the manufacturing plant where the spar section 4 is manufactured, but is not limited to this. As will be described later, when towing the spar section 4, it may be towed in segmented form, and the operation of connecting (stacking) the segments may be carried out on a workboat, for example, in a predetermined body of water (for example, the second body of water AREA2 described later). Alternatively, as will be described later, when connecting the ballast section 3 and the spar section 4 in the sea, the operation of connecting (stacking) the segments sequentially from the bottom-dwelling configuration may be carried out underwater, such as connecting the ballast section 3 and the leg section 41 underwater, and then connecting the leg section 41 and the main body section 42 underwater.

[0043] The spur section 4 may, but is not limited to, have a total length of 100m or more.

[0044] The floating structure 1, having the configuration described above, floats in the final installation area offshore (the third water area AREA3, described later) as shown in Figure 1, and wind power generation is performed. Although not shown in Figure 1, the floating structure 1 floating in the final installation area is moored by mooring ropes or the like.

[0045] Incidentally, floating offshore wind power generation facilities, as shown in Figure 1, have traditionally required construction in the open ocean (deep-water areas). However, construction in the open ocean is subject to harsh weather and sea conditions, and it may not be possible to secure sufficient construction time by work vessels, making it difficult to maintain an appropriate operating rate. For example, if sea conditions are severe, and favorable conditions such as wind speeds of around 0.5 m / s occur only once a month, it is conceivable that managing the progress of the construction process will be difficult.

[0046] The reason for the low operational rate is that the floating structure and the work vessel both move, resulting in relative motion between the two floating structures, which limits the accuracy of construction. Therefore, in this embodiment, in order to establish a construction method that can reduce the period of offshore construction, we propose a construction method for floating structure 1 (Figure 1) that focuses on the motion of the floating structure itself in order to suppress the relative motion.

[0047] <Construction methods for floating structures> Figure 3 shows a flowchart of the construction method for the floating structure 1 (Figure 1) of this embodiment. Figures 5 onwards schematically show each step of the construction method flowchart. The outline of construction method S10, as shown in Figure 3, includes the placement step S1, the ballast loading step S2, the first towing step S3, the sinking step S4, the connection step S5, the wind turbine installation step S6, the floating step S7, and the second towing step S8.

[0048] <Placement process S1> In the placement process S1, the ballast section 3 is placed in the first water area while floating. The ballast section 3 alone indicates that the spar section 4 is not connected and that the ballast has not yet been added.

[0049] In the placement process S1, the "first water area" where only the ballast section 3 floats is the first water area AREA1 shown as an example in Figure 5. For the sake of explanation, in Figures 5 and beyond, the internal space of the ballast section 3 is visible and the state in which the ballast 50 has been placed is schematically shown.

[0050] The first water area, AREA1, is, for example, located within a harbor or in a sea area where the wave height is 1.5m or less, preferably 1.0m or less. In other words, the first water area, AREA1, is not a deep sea area like the open ocean, but a shallow and calm water area. Within a harbor, the wave height is 1.5m or less and the water is calm. Furthermore, not limited to within a harbor, water areas (sea areas) adjacent to islands or surrounded by peninsulas are also calm water areas with a wave height of 1.5m or less. Note that the wave height being 1.5m or less or 1.0m or less does not necessarily have to be the case throughout the year; it may be 1.5m or less or 1.0m or less within the period allowed as part of the construction plan, or the average wave height over a specified period (for example, the period allowed as part of the construction plan, or one year) may be 1.5m or less or 1.0m or less. The condition that the wave height is 1.5m or less can be considered a condition that allows for the stable loading of ballast into the ballast section 3 by work vessels such as hopper carriers. Furthermore, the condition that the wave height is 1.0m or less can be considered a condition that allows for even more stable loading of ballast into the ballast section 3 by work vessels such as hopper carriers.

[0051] Furthermore, the first water area, AREA1, does not necessarily have to be within a harbor; it may be located in a dock or yard. A dock or yard is, for example, a tank located in a manufacturing plant that produces ballast 3. It is also called a launching pool. The first water area, AREA1, will be described later.

[0052] The deployment process S1 will be explained using Figure 4. The deployment process S1 includes the ballast section manufacturing process S1a and the ballast section launching process S1b. The ballast section manufacturing process S1a involves manufacturing a bottomed cylindrical ballast section 3 in a dock or yard. The ballast section launching process S1b involves launching the ballast section 3 manufactured in the ballast section manufacturing process S1a. The ballast section manufacturing process S1a and the ballast section launching process S1b may be carried out in the same dock or yard, or in separate locations. If the area where the ballast section 3 is launched in the ballast section launching process S1b meets the depth conditions of the first water area AREA1 described later, the launching location (launching area) becomes the first water area AREA1. However, if the conditions are not met, the process may include towing the ballast section 3 launched at the launching location (launching area) to the first water area AREA1.

[0053] <Ballast loading process S2> In the ballast loading process S2, ballast is loaded onto the ballast section 3 that was made floating in the first water area AREA1 by the placement process S1. The ballast is loaded using a work vessel such as a ballast carrier. In the ballast loading process S2, a predetermined amount of ballast is loaded.

[0054] The predetermined amount of ballast can be rephrased as the amount of ballast necessary for the ballast section 3, into which the predetermined amount of ballast has been added, to obtain a predetermined first draft in the first water area 1. The predetermined draft (first draft) is the draft at which the ballast section 3 can stably float in the first water area 1 and can be stably towed in the subsequent first towing process. The amount of ballast required to obtain the predetermined draft (first draft) can be predetermined based on the shape and weight of the ballast section 3. Typically, the predetermined draft (first draft) is in the range of 30% to 80% of the height of the ballast section 3 (H3 in Figure 5) from the bottom of the ballast section 3.

[0055] The predetermined amount of ballast, that is, the amount of ballast required for the ballast section 3 to obtain the first draft, can be calculated in advance at the construction planning stage. However, when the buoyancy of the ballast section 3 is insufficient relative to the total planned input weight of ballast, another floating structure as a temporary member may be connected to the ballast section 3 as an auxiliary floating body, so that the ballast section 3 and the auxiliary floating body integrally exert buoyancy to ensure the first draft.

[0056] The ballast section 3 into which the predetermined amount of ballast has been input in the ballast input step S2 obtains the first draft, which is the predetermined draft, in the first water area AREA1. FIG. 5 shows the first draft La.

[0057] In other words, the first water area AREA1 is a water area (sea area) having a depth greater than the first draft La, which is the predetermined draft of the ballast section 3 in a state where the spar section 4 is not connected and a predetermined amount of ballast is input into the internal space. Further, the depth of the first water area AREA1 is greater than the height of the ballast section 3 (H3 in FIG. 5).

[0058] Here, the depth may be the depth from the water surface to the water bottom (seabed), and may be synonymous with water depth. The depth of the first water area AREA1 shown as an example in FIG. 5 is denoted as WD1 in FIG. 5. Note that, when any structure is sunk on the seabed, the depth may not be the depth from the water surface (sea surface) to the seabed, but may be the depth from the sea surface to the upper surface of any structure sunk on the seabed.

[0059] The first draft La and the depth WD1 of the first water area AREA1 satisfy the relationship of La<WD1.

[0060] Further, the first water area AREA1 is a region having a depth smaller than the height of the lower structure 2 (that is, the sum of the height of the ballast section 3 and the height of the spar section 4 in a state where the spar section 4 is connected to the ballast section 3).

[0061] <First towing step S3> The first towing process S3 involves towing the ballast section 3, which has achieved a first draft La after the ballast loading process S2 has been completed, by a tugboat while keeping it afloat. The first towing process S3 involves towing the ballast section 3 into the "second water area". Figure 6 schematically shows the first towing process S3. The "second water area" is a water area that is deeper than the first water area AREA1 and shallower than the height of the substructure 2 (i.e., the sum of the height of the ballast section 3 with the spar section 4 connected to it and the height of the spar section 4). The "second water area" is the second water area AREA2 shown as an example in Figure 6. The depth of the second water area AREA2 is shown as WD2 in Figure 6. The relationship between the depth WD1 of the first water area AREA1 and WD2 is WD1 <WD2である。

[0062] <Sinking process S4> The sinking process S4 is the process of sinking the ballast section 3 to the seabed of the second water area, AREA2. Figure 7 schematically shows the sinking process S4.

[0063] In the sinking process S4, in the second water area AREA2, the ballast section 3 is suspended by a work vessel intended for sinking and holding, and water is poured into the ballast section 3 to sink it into the sea in the second water area AREA2 and allow it to settle on the seabed 200 of the second water area AREA2. If the ballast section 3 is fitted with the aforementioned auxiliary buoyancy devices, it is preferable to remove the fittings.

[0064] In the sinking process S4, the seabed 200 on which the ballast section 3 is settled is, for example, the seabed. However, if there is a structure already sunk in the sea instead of the seabed, placing the ballast section 3 on that structure may also be considered as sinking in this process.

[0065] <Connection process S5> The connection process S5 is the process of connecting the spar section 4 to the ballast section 3, which was sunk to the seabed in the sinking process S4, while raising it. To do this, it is necessary to position (tow) the spar section 4 on the sea surface in the area where the sunk ballast section 3 is located (second water area AREA2). The process up to the positioning of the spar section 4 on the sea surface in the area where the sunk ballast section 3 is located will be explained using Figure 8. Note that each step explained using Figure 8 is included in the construction method of this embodiment.

[0066] The spar manufacturing process Ssp1 shown in Figure 8 is the process for manufacturing the spar 4. The spar manufacturing process Ssp1 involves manufacturing the spar 4 at a manufacturing plant located on land (for example, in a port). At this time, the spar to be manufactured may be manufactured as a whole, or only a part of it (for example, only the leg portion 41, which will be described later) may be manufactured. If the spar 4 is in the form of a spar made by connecting divided parts as described above, the process also includes manufacturing the divided parts individually.

[0067] The spar launching process Ssp2 shown in Figure 8 is the process of launching the spar 4 manufactured in the spar manufacturing process Ssp1. The launching location may be a tank (e.g., a dock or yard) located within the manufacturing plant, but is not limited to this; it may also be a waterfront area within a port.

[0068] The spar towing process Ssp3 shown in Figure 8 is the process of towing the spar section 4 to the second water area AREA2. In the spar towing process Ssp3, the elongated spar section, which extends vertically in the final configuration of Figure 1, is towed in a horizontal position. Note that the spar towing process Ssp3 may be included in the aforementioned first towing process S3.

[0069] The connection process S5 includes a process of flooding the spar section 4, which has been towed to the surface of the second water area AREA2 by the spar section towing process Ssp3, with water and righting the spar section, which was lying on its side, into a vertical position. The righting can be done using the same method as for righting conventional spar-type floating bodies, so a detailed explanation is omitted here. The righted spar section 4 is then held upright using a workboat. The process up to this point is shown in Figure 9. The trajectory of the righted spar section 4 is indicated by an arrow. The righted cylindrical spar section 4 is in a position where the central axis of its cylinder extends almost vertically. The height of the spar section 4 mentioned above can be rephrased as the vertical length of the cylindrical spar section 4 in a position where its central axis extends almost vertically.

[0070] The connection process S5 includes the step of further lowering the upright spar section 4 toward the seabed and connecting it underwater to the ballast section 3 that has been sunk to the seabed. In order to further lower the upright spar section 4, for example, the ballast section 3 is suspended from a workboat intended for sinking and holding, and water is poured into the cylinder of the spar section 4, lowering it to the vicinity of the ballast section 3 that has been sunk to the seabed. This spar section lowering process is schematically shown in Figure 10.

[0071] As mentioned above, the depth WD2 of the second water area AREA2 shown in Figure 10 is shallower than the height of the substructure 2 (i.e., the sum of the height of the ballast section 3 and the height of the spar section 4 when the spar section 4 is connected to the ballast section 3). Therefore, in the connection process S5, when the spar section 4 and the ballast section 3 are connected underwater (the state in which the substructure 2 is formed), the upper end of the spar section 4 protrudes from the water surface into the air.

[0072] Here, an example of a method for connecting the spar section 4 and the ballast section 3 underwater in connection step S5 will be explained using Figure 11. The left side of Figure 11 shows a plan view of the ballast section 3 with the spar section 4 connected, and the right side shows a side view thereof.

[0073] As shown in Figure 11, positioning structures 3a and 4a are provided on the sides of the ballast section 3 and the spar section 4 (specifically, the leg section 41). The positioning structures 3a and 4a may, but are not limited to, have shapes that engage or fit together with each other. Alternatively, they may be configured in such a way that their positions can be identified from the outside, like markers. As an example, the configuration shown in Figure 11 is one in which the positioning structures 3a and 4a fit together.

[0074] As shown in Figure 11, the positioning structure 3a provided on the ballast section 3 is configured such that the tip of the positioning structure 3a fits with the tip of the positioning structure 4a provided on the spur section 4. Here, the tip of the positioning structure 4a provided on the spur section 4 has a tapered convex portion 4aa. Also, the tip of the positioning structure 3a has a tapered concave portion 3aa. The convex portion 4aa fits into the concave portion 3aa. Therefore, by adjusting the position of the spur section 4 so that these can fit together and sinking it toward the ballast section 3, the relative position between the ballast section 3 and the spur section 4 is determined.

[0075] The positioning configuration may also be in other forms. For example, it may be in the configurations shown in Figures 12 and 13.

[0076] Figure 12 shows another example for positioning, with a plan view on the left of Figure 12 showing the ballast section 3 connected to the spar section 4, and a side view on the right. In the example of Figure 12, guide wires 300 are connected to each of the multiple wire fixing sections 3b provided on the outer wall of the ballast section 3. The guide wires 300 are connected to the onboard winch of the workboat through an annular or cylindrical wire guide 4b having a through hole provided on the side of the spar section 4 (specifically the leg section 41) at a position corresponding to the wire fixing section 3b. In this embodiment, in the connection step S5, the relative position of the ballast section 3 and the spar section 4 can be determined by applying a predetermined tension to each guide wire 300 and then lowering the spar section 4 (specifically the leg section 41) along each guide wire 300.

[0077] The configuration shown in Figure 13 differs from the positioning configurations in Figures 11 and 12 in that the positioning guide material 110 is installed on the seabed surrounding the ballast section 3, which is submerged in the sea, rather than on the ballast section 3 and spar section 4 themselves. The left side of Figure 13 shows a plan view of the ballast section 3 with the spar section 4 connected, and the right side shows a side view thereof.

[0078] In the configuration shown in Figure 13, three columnar sections 111 constituting the guide material 110 are arranged around the ballast section 3. The columnar sections 111 are driven into the seabed 200. The spacing and relative positions of the columnar sections 111 are predetermined, and the spar section 4 is lowered to fit into the space determined by the three columnar sections 111, thereby aligning it with the ballast section 3. In other words, the configuration shown in Figure 13 includes a guide installation step in which the guide material 110 is installed on the seabed around the ballast section 3, which is sunk in the seabed 200, after the sinking process and before or during the connection process when connecting the ballast section 3 and the spar section 4. Then, in the connection step S5, when connecting the spar section 4 to the ballast section 3, the relative position of the ballast section 3 and the spar section 4 (leg section 41) can be determined by lowering the spar section 4 while bringing it into contact with the guide material 110 (columnar sections 111).

[0079] The positioning guide material 100 shown in Figure 13 may be used in combination with either of the positioning configurations shown in Figures 11 and 12.

[0080] Figure 14 is a schematic cross-sectional view showing an example of how the spar section 4 is connected to the ballast section 3 after the alignment described above has been performed. In the example shown in Figure 14, the spar section 4 (leg section 41) and the ballast section 3 are joined by a hydraulic joint. The hydraulic joint is a method used in the construction of immersed tunnel sections.

[0081] In the example shown in Figure 14, as shown in the upper part of Figure 14, a rubber gasket 400 is provided at the contact point between the spar section 4 (leg section 41) and the ballast section 3. Specifically, an annular rubber gasket 400 is provided at the end (second annular region) of the spar section 4 (leg section 41) on the ballast section 3 side. Using the pressure caused by the weight of the spar section 4 and the water pressure, the rubber gasket 400 is pressed against the edge (first annular region) surrounding the opening of the ballast section 3, and the spar section 4 (leg section 41) and the ballast section 3 are joined together (shown in the center of Figure 14). In this state, the interior enclosed by the spar section 4 and the ballast section 3 is further drained. As a result, the pressure in the internal space enclosed by the spar section 4 and the ballast section 3 becomes smaller than the water pressure caused by seawater, and the joined state between the spar section 4 (leg section 41) and the ballast section 3 can be maintained.

[0082] To drain the interior, a drain pipe 45 is inserted through the leg portion 41, draining the water from the interior surrounded by the spar portion 4 and the ballast portion 3. The drain pipe 45 is connected to a drain pump (not shown). A drain pump is installed on a workboat, for example. The drain pipe 45 may also extend along the inside of the main body portion 42 of the spar portion 4 to the upper end of the spar portion 4.

[0083] The joint between the spur section 4 (leg section 41) and the ballast section 3 can be sealed to a certain degree of watertightness by the above process. However, in order to achieve even greater watertightness, the interior enclosed by the spur section 4 and the ballast section 3 may be filled with mortar 600. The mortar may be filled by installing piping etc. in advance inside the interior enclosed by the spur section 4 and the ballast section 3, connecting the piping etc. to the air-filled section, and using this piping etc. for filling.

[0084] For example, if the connection process S5 shown in Figure 14 is performed at a water depth of approximately 100m, the bottom area of ​​the internal space of the ballast section 3 is 400m². 2 Assuming this is the case, the pressure exerted on the lower surface (the surface in contact with the seabed) of the ballast section 3 when the spar section 4 (leg section 41) and the ballast section 3 are joined is approximately 40,000 tons (= bottom area of ​​400 m²). 2 ×Water depth 100m ×Specific gravity of water 1.03 t / m³ 3 ) can be estimated as follows. And, for example, if we estimate that the amount of ballast put into the ballast section 3 is about 20,000 tons, and the weight of the structure of the ballast section 3 is about 10,000 tons, the total will be about 30,000 tons, so the water pressure from the bottom surface of the ballast section 3 will not cause the spar section 4 (leg section 41) and the ballast section 3 to separate.

[0085] Although the spar section 4 (leg section 41) and the ballast section 3 are connected by hydraulic bonding in this manner, the connection between the spar section 4 (leg section 41) and the ballast section 3 may be further secured using fixing means (not shown).

[0086] The left side of Figure 15 shows how the spar section 4 is connected to the ballast section 3 by the underwater connection described above in connection step S5.

[0087] <Windmill installation process S6> Following the connection process S5, a wind turbine installation process S6 is performed, in which the wind turbine 51 is installed on the upper part of the spar section 4 (main body section 42) of the substructure 2 (connecting structure). The wind turbine installation process S6 is shown on the right side of Figure 15. The wind turbine installation process S6 is performed in the second water area 2 where the connection process S5 was carried out. In other words, the substructure 2 completed in the connection process S5 is not floated or moved, but the wind turbine installation process S6 is performed in the second water area 2 as is.

[0088] As mentioned above, since the depth WD2 of the second water area AREA2 is shorter than the total length of the substructure 2, the connection of the wind turbine 51 to the upper part of the spar section 4 (main body section 42) in the wind turbine installation process S6 is performed in the atmosphere. Since the wind turbine 51 is installed while the substructure 2 is settled on the seabed 200, the oscillation of the floating body itself, which is a problem in conventional construction, does not occur. The wind turbine 51 can be assembled using a crane ship.

[0089] Here, it is preferable that the surface of the seabed (seabed) at depth 200 is a horizontal plane or has a small slope that is close to horizontal. Based on the preliminary survey, a second body of water should be selected so that an area with minimal unevenness can be designated as the second body of water. If it is difficult to select such an area, it may be possible to select a more suitable area and construct a rubble mound there.

[0090] The wind turbine installation process S6 is carried out under conditions that facilitate work by ships. For example, the second water area AREA2 may be a sea area where the average wave height over a specified period (e.g., the period allowed as the construction period in the construction plan, or one year) is 0.5m or less. In addition, the weather conditions for the second water area AREA2 may be calm weather with wind speeds of 10m / s or less.

[0091] In the wind turbine installation process S6, the floating structure 1, which includes the lower structure 2 and the wind turbine 51 installed on top of the lower structure 2, is completed in a state where it is submerged in the seabed 200 (shown on the right side of Figure 15).

[0092] <Floating process S7> The floating process S7 is the process of raising the floating structure 1 (a floating structure 1 equipped with a ballast section 3, a spar section 4, and a wind turbine 51), which was completed in the wind turbine installation process S6, from the seabed 200. The floating process S7 is carried out by draining the seawater that has been poured into the lower structure 2 using a workboat. Figure 16 schematically shows the floating structure 1 in a state raised by the floating process S7 on the left side of the drawing. Note that the drawing illustrates a state in which all the water in the cylinder of the spar section 4 has been drained, but this is not the only example.

[0093] <Second towing process S8> The second towing process S8 is the process of towing the floating structure 1, which was raised in the surfacing process S7, to the sea area (third water area) where the offshore wind power generation facility will be constructed. The right side of Figure 16 schematically shows the floating structure 1 being towed to the third water area AREA3, which is the sea area where the offshore wind power generation facility will be constructed. The towing is carried out by a tugboat.

[0094] The depth WD3 of the third water area AREA3 is deeper than the depth WD2 of the second water area AREA2. Furthermore, the depth WD3 of the third water area AREA3 is deeper than the second draft, which is a predetermined draft of the floating structure 1 (Figure 1). The second draft L1 is shown on the right side of Figure 16. The second draft L1 of the floating structure 1 depends on the size of the superstructure 5 (wind turbine 51 in the example of Figure 1) attached to the substructure 2 shown in Figure 1. In one example, the second draft L1 can be between 60m and 100m.

[0095] In the third water area, AREA3, the mooring ropes and submarine cables that had been prepared in advance are connected to floating structure 1. This completes the construction of floating structure 1.

[0096] According to the construction method of this embodiment, the floating structure is configured as a two-part structure consisting of a ballast section 3 and a spar section 4, which are connected together. Therefore, the ballast loading work, which is conventionally carried out in the open sea, can be carried out in shallow, calm waters, thus reducing the construction period.

[0097] Furthermore, since the substructure 2 is resting on the seabed 200 after the ballast section and spar section are connected underwater, there is no motion of the substructure 2 itself. If there is no motion, the relative motion between the two floating bodies can be suppressed more than in conventional construction, which is expected to reduce the construction period for wind turbine assembly work using a crane ship.

[0098] Furthermore, the spar section 4 may be large, exceeding 100m in total length, or even gigantic, reaching 200m in length. Even with a floating structure 1 having a relatively long spar section 4, according to this embodiment and the construction method, it is connected to the ballast section 3 sunk to the seabed, thus suppressing the effects of motion and enabling smooth construction.

[0099] Furthermore, according to this embodiment, the ballast section 3, without the spar section 4 connected, is placed in the first water area AREA1 and the ballast is added. As a result, there is no need to lift the ballast to a high position as in the construction method described in Patent Document 1, and as a secondary effect, the energy efficiency when adding the ballast can be improved.

[0100] Furthermore, according to this embodiment, since the ballast section 3 and the spar section 4 are manufactured separately, it is possible to provide a spar-type floating structure with a longer overall length than conventional structures, even when there are constraints on the size (volume) of the dock or yard. For example, when manufacturing a spar-type substructure 2 with a long overall length, if the substructure 2 is to be manufactured as a single unit, it may not be possible to manufacture it in an existing dock or yard. If manufacturing is not possible in an existing dock or yard, expanding the dock or yard is costly, and developing a new manufacturing plant is not easy. In contrast, according to this embodiment, since the ballast section 3 and the spar section 4 are manufactured separately, they can be manufactured in an existing dock or yard.

[0101] Since the depth of the second water area AREA2 (connecting water area) connecting the ballast section 3 and the spar section 4 is greater than the height of the ballast section 3, buoyancy due to seawater acts on at least a portion of the spar section 4 connected to the ballast section 3. Furthermore, since the ballast section 3 is submerged on the seabed of the second water area AREA2 and the spar section 4 is connected to the ballast section 3 while partially or entirely standing upright, lateral forces acting perpendicular to the axis (central axis) of the spar section 4 are less likely to act. Due to these factors, the force required to handle the spar section 4 in the connection process S5 is reduced by buoyancy, and forces that would try to knock down the upright spar section 4 are less likely to act on it, thus making the handling of the spar section 4 in the connection process S5 easier.

[0102] <Floating Structure Kit> As described above, according to the construction method of this embodiment, a floating structure comprising a ballast section and a spar section can be obtained by separately manufacturing the ballast section and the spar section in a dock or yard and connecting the ballast section and the spar section in the sea. Therefore, this embodiment can be rephrased as being able to provide a floating structure kit comprising the ballast section 3 and the spar section 4 described above. The floating structure kit consists of a ballast section 3 that is not connected to the spar section 4 and a spar section 4 that has an annular rubber gasket 400 at its end as described above. The annular rubber gasket 400 may be positioned to surround the opening at the upper end of the ballast section 3, rather than at the end of the spar section 4 (leg section 41).

[0103] The spar section 4 of this floating structure kit may also be composed of multiple segments, as described above, or all or only some of the multiple segments may be included as components.

[0104] This floating structure kit can also function as a kit for the lower structure 2. Alternatively, this floating structure kit may also include the wind turbine 51 (superstructure).

[0105] <Floating structure assembled using a floating structure kit> Furthermore, this embodiment may include a floating structure assembled using the floating structure kit described above. Specifically, it may include a floating structure 1 (lower structure 2) in which the ballast section 3 and the spar section 4 are connected using the kit, with the internal space sealed by an annular rubber gasket 400 interposed between a first annular region surrounding an opening formed in the ballast section 3 and a second annular region forming the end of the spar section 4 on the ballast section 3 side. In this configuration, the pressure in the internal space is smaller than the water pressure caused by seawater.

[0106] [Embodiment 2] Other embodiments of the present invention are described below. For the sake of clarity, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0107] Embodiment 1 includes a placement step S1 in which only the ballast section 3 before ballast is added is placed in a first water area AREA1 having a depth WD1, and a ballast addition step S2 in which ballast is added to the ballast section 3. In contrast, the construction method for the floating structure of this embodiment does not include the placement step S1 and the ballast addition step S2, but instead places the ballast section on a part of the bottom of the tank and adds ballast, then fills the tank with water to form the first water area described in Embodiment 1, and floats the ballast section 3 after ballast addition in the first water area AREA1.

[0108] Figure 17 shows a flowchart of the construction method for the floating structure of this embodiment. The construction method S10' of the floating structure of this embodiment generally includes the placement step S1' and the floating step S2' in place of the placement step S1 and the ballast loading step S2 described in Embodiment 1, and the steps from the first towing step S3 onward include the first towing step S3, the sinking step S4, the connection step S5, the wind turbine installation step S6, the surfacing step S7, and the second towing step S8, the same as in Embodiment 1.

[0109] <Placement process S1'> The placement step S1' involves placing the ballast section 3, which has its spar section unconnected and has ballast placed in its internal space, onto a portion of the bottom of a tank. The tank could be, for example, the tank 80 shown in Figure 18. Tank 80 is, as one example, a dock or yard for manufacturing the body of the ballast section 3.

[0110] In the placement process S1', the ballast section 3 may be manufactured in the tank 80, or it may be manufactured elsewhere, transported to the tank 80, placed in a portion of the bottom of the tank 80, and then ballast is placed into the internal space.

[0111] <Floating process S2'> In the floating process S2', after the placement process S1', water is poured into the tank 80 to form a first water area, and the ballast section 3 is floated in the formed first water area. The tank 80 is located on the shore of the harbor, and water can be poured into the tank 80 by drawing in bay water (seawater). This state is shown in the lower part of the drawing in Figure 18. In this state, the ballast section 3 has a predetermined draft, a first draft La, due to the amount of ballast that has been added. The water depth WD1' of the first water area AREA1 in the tank 80 is deeper than the first draft La. Furthermore, this water depth WD1' is shallower than the sum of the heights of the ballast section 3 and the spar section 4 when the spar section 4 is connected to the ballast section 3 (as shown in Figure 2).

[0112] The ballast section 3, having obtained a first draft La through the floating process S2', moves from the tank 80 to the sea, and the processes from the first towing process S3 onward are carried out, just as in Embodiment 1.

[0113] In the construction method of this embodiment, as in Embodiment 1, the ballast can be placed into the internal space of the ballast section, which is a standalone unit with the spar and wind turbine not connected, in a tank located in a calm area such as a dock or yard. Therefore, it is less susceptible to adverse weather and sea conditions compared to the upright location in the construction method described in Patent Document 1. As a result, the construction period for the floating structure 1 (Figure 1, etc.) can be shortened.

[0114] According to the above configuration, a construction method for spar-type floating structures can be provided that is less susceptible to adverse weather and oceanographic conditions. Such effects contribute to achieving, for example, Goal 7 of the United Nations' Sustainable Development Goals (SDGs), "Ensure access to affordable, reliable, sustainable, and modern energy for all."

[0115] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0116] 1. Floating structure 2 Substructure 3. Ballast section 3a Positioning structure 3aa recess 3b Wire fixing section (positioning structure) 4. Sparring Club 4a Positioning structure 4aa protrusion 4b Wire guide (positioning structure) 5 Superstructure 41 Legs 42 Main body 50 ballast 51 Windmill 52 Pillar 53 Nasser 54 Blades 80 tanks (dock or yard) 110 Guide material 111 Column section 200 Underwater (underwater) 300 guide wires 400 Rubber Gasket AREA1, Area 1 AREA2 Second Water Area (Contiguous Zone) AREA3 Third Water Area (Floating Structure Installation Area) La 1st draft L1 Second Draft

Claims

1. A method for constructing a floating structure comprising a bottomed cylindrical ballast section having an opening at its upper end, a cylindrical spar section connected to the upper end, and a wind turbine connected to the spar section, A placement step of placing the ballast section in a floating state, with the spar section unconnected and before the predetermined amount of ballast is added, in a first body of water having a depth deeper than a first draft which is a predetermined draft of the ballast section in a state where the spar section is unconnected and a predetermined amount of ballast has been added to its internal space, and shallower than the sum of the height of the ballast section and the height of the spar section in a state where the spar section is connected to the ballast section, The process includes a ballast loading step in which a predetermined amount of ballast is loaded into the internal space of the ballast section, which is floating in the first body of water as a result of the arrangement step, in order to obtain the first draft, Construction methods for floating structures.

2. A method for constructing a floating structure comprising a bottomed cylindrical ballast section having an opening at its upper end, a cylindrical spar section connected to the upper end, and a wind turbine connected to the spar section, A placement step involves placing the ballast section, in a state where the spar section is not connected and ballast has been placed in its internal space, on a portion of the bottom of the tank. After the above-mentioned placement step, water is poured into the tank to form a first water area, and the ballast section is floated in the first water area in a floating step, Includes, In the floating process, the water depth of the first water area is set to be deeper than the first draft, which is a predetermined draft of the ballast section when a predetermined amount of ballast is placed in its internal space, and shallower than the sum of the height of the ballast section and the height of the spar section when the spar section is connected to the ballast section, so that the ballast section obtains the first draft in the first water area. Construction methods for floating structures.

3. The first body of water is located within a harbor or in a sea area where the wave height is 1.5 m or less. A method for constructing the floating structure described in claim 1.

4. The aforementioned first body of water is located in the dock. A method for constructing the floating structure described in claim 1.

5. A first towing step involves towing the ballast section, which has obtained the first draft in the first water area, into a second water area that is deeper than the first water area and shallower than the sum of the height of the ballast section and the height of the spar section. A sinking step of sinking the ballast section to the bottom of the second body of water, The process further includes a connection step of connecting the spar portion to the ballast portion submerged in the seabed while raising it to obtain a connection structure, A method for constructing a floating structure according to claim 1 or 2.

6. A wind turbine installation step to obtain the floating structure by installing the wind turbine on the upper part of the spar portion of the connecting structure, A floating step is to raise the floating structure obtained by the wind turbine installation step above from the seabed, A second towing step involves towing the floating structure, which has been brought to the surface by the surfacing step, into a third water area whose depth is greater than the second water area and which is greater than the second draft, which is a predetermined draft of the floating structure. This also includes, A method for constructing the floating structure described in claim 5.

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