Floating structures

Abstract

This allows the floating structure to be easily aligned with the flow direction, and reduces the drag force acting on the floating structure when it is aligned with the flow direction. [Solution] The floating structure 2 comprises a floating body 21 that extends in the front-rear direction and to which a mooring line is directly or indirectly connected, and an extension portion 26 attached to the rear end 25 of the floating body 21 in the front-rear direction, extending continuously rearward from both sides 252 of the rear end 25, and having a pair of extension surfaces 264 that move closer to each other as they move towards the rear. The extension portion 26 has a water-filled space P into which water enters between the pair of extension surfaces 264, and the mooring line is connected to the front of the center of the floating structure 2 in the front-rear direction. This makes it easy to orient the floating structure 2 directly toward the flow direction and reduces the drag force acting on the floating structure 2 when it is facing the flow direction.

Description

Technical Field

[0001] The present invention relates to a floating structure.

Background Art

[0002] In recent years, in order to observe tsunamis and waves, floating structures (also called GPS wave gauges buoys, etc.) equipped with GPS (Global Positioning System) receivers have been used. As such a floating structure, in Patent Document 1, a catamaran-type floating structure in which two floating body main bodies are connected has been proposed. In this floating structure, by connecting a mooring line to the front side of the center of gravity, the front end portion of the floating body main body is likely to face the upstream side in the direction of the external force. As a result, the longitudinal direction of the floating body main body becomes substantially parallel to the direction of the external force, and it becomes possible to reduce the load (or mooring tension) acting on the mooring line. Further, in Patent Document 1, a method of further facilitating the front end portion of the floating body main body to face the upstream side in the direction of the external force by fixing a skeg to the rear end portion of the floating body main body is also disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, even when the longitudinal direction of the floating body main body is made substantially parallel to the flow direction of water such as tidal currents, that is, when the floating structure is made to face directly, for example, depending on the shape of the rear end portion of the floating structure, flow separation occurs, and the drag acting on the floating structure increases. Therefore, there is a need for a method of easily making the floating structure face directly in the flow direction and reducing the drag acting on the floating structure in the state of facing directly in the flow direction.

[0005] This invention has been made in view of the above problems, and aims to easily orient a floating structure directly toward the flow direction and to reduce the drag force acting on a floating structure in a state where it is oriented directly toward the flow direction. [Means for solving the problem]

[0006] One aspect of the present invention is a floating structure moored by a mooring line, comprising: a floating body extending in the front-rear direction and to which the mooring line is directly or indirectly connected; and an extension portion attached to the rear end of the floating body in the front-rear direction, extending continuously rearward from both sides of the rear end, and having a pair of extension surfaces that move closer to each other as they move towards the rear, wherein the extension portion has a water-filling space between the pair of extension surfaces into which water enters, and the mooring line is connected to a position forward of the center of the floating structure in the front-rear direction.

[0007] Aspect 2 of the present invention is a floating structure according to aspect 1, wherein the flooded space is enclosed on all four sides and has an opening at the top and / or bottom.

[0008] A third aspect of the present invention is a floating structure according to aspect 1 (or aspect 1 or 2), wherein the pair of extended surfaces are the surfaces of a pair of plate-like portions.

[0009] A fourth aspect of the present invention is the floating structure of the third aspect, wherein the pair of plate-like portions move closer to each other as they extend towards the rear, and their rear ends are connected.

[0010] Aspect 5 of the present invention is a floating structure according to Aspect 1 (which may be any one of Aspects 1 to 4), wherein the rear end of the floating body has an end face that forms a corner together with each of the two side faces, and each of the pair of extended surfaces extends rearward from the corner.

[0011] Aspect 6 of the present invention is a floating structure according to any one of aspects 1 to 5, wherein the floating body has a front end, a front body, and a rear body along the longitudinal direction, the rear end is included in the rear body, and in the front end, the front body, and the rear body, the drag per unit length in the longitudinal direction against a flow in the width direction perpendicular to the longitudinal and vertical directions is minimized at the front end and maximized at the rear body.

[0012] Aspect 7 of the present invention is a floating structure according to aspect 6, wherein the front end portion is formed of foam. [Effects of the Invention]

[0013] According to the present invention, it is possible to easily orient a floating structure directly toward the flow direction and suppress flow separation in a floating structure that is oriented toward the flow direction, thereby reducing the drag force acting on the floating structure. [Brief explanation of the drawing]

[0014] [Figure 1] This is a diagram showing the configuration of the mooring system. [Figure 2] This is a side view showing a floating structure. [Figure 3] This is a plan view showing a floating structure. [Figure 4] This is a front view showing a floating structure. [Figure 5] This is a plan view showing a floating structure having a single floating body and an extension. [Figure 6A] This is a longitudinal cross-sectional view showing the rear fuselage. [Figure 6B] This is a longitudinal cross-sectional view showing the front of the fuselage. [Figure 6C] This is a longitudinal cross-sectional view showing the front end. [Figure 7A] This diagram illustrates the movement of a floating structure facing the direction of flow. [Figure 7B] This diagram illustrates the movement of a floating structure facing the direction of flow. [Figure 7C]This is a diagram for explaining the operation of the floating structure facing directly against the flow direction. [Figure 8] This is a diagram showing the floating structure of the comparative example. [Figure 9A] This is a diagram showing another example of the floating structure. [Figure 9B] This is a diagram showing another example of the floating structure. [Figure 9C] This is a diagram showing another example of the floating structure. [Figure 9D] This is a diagram showing another example of the floating structure. [Figure 10] This is a diagram showing another example of the floating structure. [Figure 11A] This is a diagram showing another example of the floating structure. [Figure 11B] This is a diagram showing another example of the floating structure. [Figure 11C] This is a diagram showing another example of the floating structure. [Figure 12] This is a diagram showing another example of the floating structure.

Embodiments for Carrying Out the Invention

[0015] FIG. 1 is a diagram showing the configuration of a mooring system 1 according to an embodiment of the present invention. The mooring system 1 includes a floating structure 2, a mooring base 3, and a mooring line 4. The mooring system 1 is a system for mooring the floating structure 2 floating on the water surface 91 to the seabed 92 by the mooring line 4. The floating structure 2 is a structure that floats on the water surface 91 in a state separated upward from the seabed 92. In the present embodiment, the floating structure 2 is installed on the sea, and the water surface 91 and the seabed 92 are the sea surface and the seabed, respectively. The floating structure 2 is, for example, an observation buoy moored in a predetermined sea area for observing tsunamis and / or waves. The overall length of the floating structure 2 is, for example, several meters to a dozen or so meters, and the overall width of the floating structure 2 is, for example, several meters. The floating structure 2 may be installed other than on the sea.

[0016] The mooring base 3 is an object fixed to the seabed 92. The mooring base 3 is, for example, a sinker (i.e., a weight) or an anchor (i.e., an anchor with holding power) submerged in the seabed 92. Alternatively, the mooring base 3 may be a fixed structure pre-installed in the seabed 92. The mooring base 3 does not necessarily have to be directly fixed to the seabed 92; for example, it may be an object indirectly fixed to the seabed 92 underwater via another structure fixed to the seabed 92.

[0017] The mooring line 4, also called a mooring rope, is a roughly linear member that connects the floating structure 2 and the mooring base 3. The mooring line 4 is, for example, a metal chain. Alternatively, the mooring line 4 may be a mooring rope, or a chain and a mooring rope connected together. The mooring rope is, for example, a rope made of synthetic fiber or metal. In Figure 1, for illustrative purposes, the mooring line 4 is shown as a line.

[0018] In the example shown in Figure 1, the floating structure 2 is moored to the mooring base 3 at one point by a single mooring line 4. Single-point mooring is a mooring method in which one floating structure 2 is connected to only one mooring base 3 provided on the seabed 92. In multi-point mooring, which is a different mooring method from single-point mooring, one floating structure is connected to two or more mooring bases provided on the seabed 92. The floating structure 2 may also be moored to the mooring base 3 by multi-point mooring.

[0019] Figure 2 is a side view of the floating structure 2. Figure 3 is a top view of the floating structure 2. Figure 4 is a front view of the floating structure 2. In Figures 2 to 4, three mutually orthogonal directions, the X, Y, and Z directions, are defined. The X and Y directions are parallel to the horizontal plane, and the Z direction is parallel to the direction of gravity (up and down). Figure 3 shows the structure with the upper connecting section 28, which will be described later, removed.

[0020] The floating structure 2 comprises two floating body sections 21, two extension sections 26, an upper connecting section 28, and a mooring section 29. The floating structure 2 is a so-called catamaran-type structure in which two floating body sections 21 are connected. As will be described later, the floating structure 2 may have only one floating body section 21, or it may have three or more floating body sections 21.

[0021] Each floating body 21 extends substantially parallel to the X direction in Figures 2 to 4 (hereinafter referred to as the "front-rear direction"). Two floating body 21s are arranged with a gap between them in the width direction perpendicular to the front-rear and up-down directions (i.e., the Y direction in Figures 2 to 4). In other words, one floating body 21 is positioned separately to the side of the other floating body 21. The shape of the two floating body 21s extends in the front-rear direction at the center of their width direction and is substantially symmetrical with respect to a plane of symmetry perpendicular to the width direction. The front-rear direction and width direction are directions defined with respect to the floating structure 2.

[0022] Each floating body 21 is elongated in the front-rear direction and has a so-called boat-shaped exterior. The floating body 21 comprises a front end 22, a front hull 23, and a rear hull 24. The front end 22, front hull 23, and rear hull 24 are connected in order from the front to the rear. In the example in Figure 3, the width in the width direction (hereinafter also simply referred to as "width") of the front hull 23 and the rear hull 24 is approximately the same, and the width of the front end 22 gradually decreases towards the front. The extension 26 is an appendage connected to the rear end 25 of the floating body 21. The rear end 25 of the floating body 21 is the part that includes the rear end of the rear hull 24. Details of the front end 22, front hull 23, rear hull 24, and extension 26 will be described later.

[0023] The upper connecting section 28 connects the upper parts of the two floating body halves 21 above the waterline of the floating structure 2 (i.e., the upper waterline in the design). The upper connecting section 28 includes an upper deck 281 that connects the upper ends of the two floating body halves 21 (i.e., the (+Z) side ends). The upper deck 281 is a substantially flat plate-shaped member that is substantially vertical in the vertical direction and is positioned above the water surface 91. The upper deck 281 is, for example, a substantially rectangular member that extends over the entire length of the floating body halves 21 in the front-rear direction. The upper deck 281 covers the entire upper surface of the two floating body halves 21 and the entire space above the space between the two floating body halves 21. The upper deck 281 does not necessarily have to be substantially rectangular and may be a member of other shapes (e.g., substantially disc-shaped). The upper deck 281 is formed from, for example, stainless steel, aluminum alloy, FRP, etc.

[0024] Various equipment and facilities are arranged on the upper deck 281 according to the intended use of the floating structure 2. As mentioned above, when the floating structure 2 is used as an observation buoy to observe tsunamis and waves, for example, a GPS (Global Positioning System) receiver 282 for acquiring the three-dimensional movement of the floating structure 2 is placed on the upper deck 281. Then, based on the movement of the floating structure 2 acquired by the GPS receiver 282, fluctuations in the water surface 91 (e.g., waves, tide level, tsunami, etc.) are acquired.

[0025] Furthermore, solar panels for supplying power to, for example, a GPS receiver 282 may be installed on the upper deck 281. If the floating structure 2 has two or more floating bodies 21, the area of ​​the upper deck 281 can be made relatively large, so that the solar panels can be arranged almost horizontally. This can increase the amount of power generated by the solar panels. It can also reduce the wind pressure resistance of the solar panels. As a result, the load (or mooring tension) acting on the mooring line 4 can be reduced. The upper connecting section 28 may be equipped with other connecting members in addition to the upper deck 281, or in place of the upper deck 281.

[0026] The mooring section 29 comprises a flat plate section 291 and two vertical pipes 292. The flat plate section 291 is a roughly plate-shaped member that extends almost vertically in the vertical direction and is positioned between the two floating body sections 21 below the upper connecting section 28. In the example shown in Figures 2 to 4, both ends of the flat plate section 291 in the width direction are fixed to the front body sections 23 of the two floating body sections 21, respectively. The flat plate section 291 is located below the waterline of the floating structure 2 (i.e., below the water surface 91). The mooring line 4 is connected to the lower surface of the flat plate section 291 at a position A1 (hereinafter referred to as "mooring point A1") which is approximately in the center in the front-rear and width directions. The mooring point A1 between the floating structure 2 and the mooring line 4 is located below the water surface 91. The two vertical pipes 292 are provided on the upper surface of the flat plate section 291 at positions that are the same distance apart on both sides from the center in the width direction. Each vertical pipe 292 connects the upper surface of the flat plate section 291 to the upper deck 281. The vertical pipes 292 fix the flat plate section 291 to the upper deck 281.

[0027] In this embodiment, the center of gravity of the floating structure 2 is located at a position different from the center of the entire floating structure 2 in the longitudinal direction (for example, rearward from the center). In the example shown in Figures 2 to 4, the center of gravity of the floating structure 2 is a composite center of gravity obtained by combining the centers of gravity of the two floating body parts 21, the two extension parts 26, the upper connecting part 28, and the mooring part 29. The mooring point A1 of the mooring part 29 is located, for example, forward of the center of gravity of the floating structure 2 in the longitudinal direction. In practice, the mooring point A1 is located forward of the center of the entire length of the floating structure 2 in the longitudinal direction. If the mooring point A1 is located forward of the center of the entire length of the floating structure 2, the flat plate part 291 may be fixed to the rear body 24. Also, the structure of the mooring part 29 may be modified as appropriate.

[0028] Next, the details of the structure of the floating body 21 and the extension 26 will be described. For the sake of simplicity, the floating structure 2 will be described as having only one floating body 21 and an extension 26. Figure 5 is a plan view showing the floating structure 2 having one floating body 21 and an extension 26. Figures 6A, 6B, and 6C are longitudinal cross-sectional views of the floating body 21 at the positions of arrows AA, BB, and CC in Figure 5, respectively. Figures 6A, 6B, and 6C show longitudinal sections of the rear body 24, front body 23, and front end 22, respectively, i.e., sections perpendicular to the front-rear direction (X direction).

[0029] As shown in Figure 6A, the cross-sectional shape of the aft fuselage 24 is substantially rectangular. The aft fuselage 24 has an upper and lower surface substantially perpendicular to the vertical direction (Z direction) and two sides substantially perpendicular to the width direction (Y direction). The upper and lower surfaces, as well as the two sides of the aft fuselage 24, are all flat surfaces. The aft fuselage 24 in Figure 6A is a hollow body with an internal space, and is manufactured, for example, by joining plate-shaped members by welding or the like. Water surrounding the float body 21 cannot penetrate the internal space. The plate-shaped members are made of, for example, stainless steel, aluminum alloy, etc. The aft fuselage 24 may be manufactured by other methods, and may be made of FRP, etc. (similar to the aft fuselage 23). In this specification, the side surfaces include surfaces facing approximately in the width direction and are not limited to surfaces perpendicular to the width direction as in Figure 6A. Furthermore, the lower surface includes surfaces that face approximately downwards and is not limited to surfaces perpendicular to the vertical direction, as shown in Figure 6A.

[0030] As shown in Figure 6B, the cross-sectional shape of the front fuselage 23 has a shape in which a roughly semicircle or roughly semiellipse is connected to the lower side of a rectangle. The upper surface of the front fuselage 23 is a flat surface that is roughly perpendicular in the vertical direction, and the upper parts of the two sides are flat surfaces that are roughly perpendicular in the width direction. The lower surface of the front fuselage 23 and the lower parts of the two sides are part of a roughly cylindrical surface or a roughly elliptical cylindrical surface. The front fuselage 23 in Figure 6B is also a hollow body with an internal space, and is manufactured, for example, by joining molded plate-like members by welding or the like. Water surrounding the float body 21 cannot penetrate into the internal space. The plate-like members are made of, for example, stainless steel, aluminum alloy, etc. Near the boundary between the front fuselage 23 and the rear fuselage 24, an appendage may be appropriately attached to avoid abrupt changes in the cross-sectional shape. The same applies near the boundary between the front end 22 and the front fuselage 23.

[0031] As shown in Figure 6C, the cross-sectional shape of the front end 22 is approximately semicircular or semi-elliptical. For example, the vertical height of the front end 22 gradually decreases towards the front (see Figure 2). The upper surface of the front end 22 is a flat surface approximately perpendicular to the vertical direction. The two sides and the bottom surface of the front end 22 are part of an approximately spherical or approximately ellipsoidal surface. The front end 22 in Figure 6C is a solid body with a solid interior, and is manufactured, for example, by molding foam. The foam material is, for example, urethane foam. The front end 22 may be manufactured by other methods.

[0032] The rear end portion 25 of the floating body 21 in Figure 5 is included in the rear fuselage 24. The rear end portion 25 has a rear end surface 251 that is substantially perpendicular to the front-rear direction and two side surfaces 252 (hereinafter referred to as "rear end side surfaces 252") that are substantially perpendicular to the width direction. The rear end surface 251 is a flat surface facing the (+X) direction. The two rear end side surfaces 252 are flat surfaces facing the (+Y) direction and the (-Y) direction, respectively. At the rear end portion 25, a corner portion 253 is formed by the rear end surface 251 and each rear end side surface 252. The angle of the corner portion 253 viewed along the vertical direction is typically substantially right angle. Depending on the design of the floating body 21, this angle may be acute or obtuse.

[0033] The extension portion 26 comprises two plate members 261 that are substantially perpendicular to the XY plane. The plate members 261 are made of stainless steel, aluminum alloy, FRP, etc. The outer shape of each plate member 261 is substantially rectangular and has two sides that are aligned vertically, and an upper end and a lower end that are substantially perpendicular to the vertical direction. The plate member 261 is roughly aligned in the front-rear direction, with one of the two sides being the front end located on the front side in the front-rear direction, and the other being the rear end located on the rear side. The front end of each plate member 261 is joined to the corners 253 of the rear end 25 of the floating body 21 by welding or the like. That is, the front ends of the two plate members 261 are joined to the two corners 253 of the rear end 25, respectively. The two plate members 261 are inclined with respect to the front-rear direction so that they move closer to each other as they move towards the rear, and the rear ends of the two plate members 261 are joined to each other by welding or the like. In the example shown in Figure 5, the rear ends of the two plate members 261 are fixed to each other on or near the center line C1 (shown as a dashed line in Figure 5), which is located in the widthwise center of the floating body 21. In a preferred example, the two plate members 261 are symmetrical with respect to a plane that includes the center line C1 and is perpendicular to the widthwise direction. Each plate member 261 can also be considered a skeg.

[0034] At each extension 26, a space P (hereinafter referred to as the "flooded space P") is formed, surrounded by two plate members 261 and the rear end surface 251 of the floating body 21. The flooded space P in Figure 5 has a triangular shape when viewed along the vertical direction and is a space surrounded on all four sides (surroundings) in the front-to-back and width directions. The flooded space P is open at the top and bottom, allowing water from around the floating structure 2 to enter. In the case where the upper deck 281 covers the extension 26, as shown in Figure 2, the upper ends of the two plate members 261 may be joined to the lower surface of the upper deck 281 by welding or the like, so that only the bottom of the flooded space P is open. In this case, the fixing strength of the two plate members 261 (extension 26) is improved. If the area above the flooded space P is blocked by the upper deck 281, through-holes or the like may be provided in the upper deck 281 to allow air to escape from the flooded space P, thereby enabling water to enter the interior of the flooded space P.

[0035] Focusing on the surface 264 (hereinafter referred to as the "extended surface 264") opposite to the submerged space P in each plate member 261, in the extended portion 26, the extended surface 264 extends continuously to the rear from the rear end side surface 252 of the rear end portion 25 (i.e., it extends to the rear). In other words, the extended surface 264 extends to the rear from the rear end side surface 252 without any large irregularities at the boundary between the rear end side surface 252 and the extended surface 264. Furthermore, the extended surfaces 264 of the two plate members 261 approach each other as they move towards the rear. In one example of the manufacturing of the floating structure 2, after the fuselage is made by joining the front fuselage 23 and the rear fuselage 24, the front end portion 22 and the extended portion 26 are attached (added later) to the front and rear sides of the fuselage, respectively.

[0036] Figures 7A to 7C illustrate the operation of the floating structure 2 facing the direction of water flow, such as tidal currents. For the sake of explanation, in Figures 7A to 7C, it is assumed that mooring point A1 is provided on the front hull 23 of the floating body 21, that is, that the mooring line 4 is directly connected to the floating body 21. The direction of flow is indicated by arrow F1 (similarly in Figure 3 and Figure 8 described later). As in Figure 7A, when the flow direction F1 is approximately parallel to the width direction of the floating structure 2, a drag force in the width direction is generated at the rear hull 24 in Figure 6A, the front hull 23 in Figure 6B, and the front end 22 in Figure 6C. The magnitude of this drag force depends on the drag coefficient and projected area when viewed along the width direction.

[0037] In the front fuselage 23 and front end 22, the cross-sectional shape of the widthwise and downward-facing portions is approximately semicircular or semielliptical, meaning the lower end is rounded. Therefore, the drag coefficients of the front fuselage 23 and front end 22 are smaller than those of the rear fuselage 24, which does not have a rounded lower end. Also, the projected area of ​​the front end 22 is smaller than that of the front fuselage 23. As a result, when comparing the rear fuselage 24, front fuselage 23, and front end 22, the drag in the widthwise direction per unit length in the longitudinal direction (hereinafter simply referred to as "drag per unit length") is smallest at the front end 22 and largest at the rear fuselage 24. Furthermore, the drag per unit length is relatively large even at the extension 26, which is located furthest from the mooring point A1. In Figures 7A and 7B, the drag per unit length is indicated by arrow D1. It can also be considered that, in the rear fuselage 24, front fuselage 23, and front end 22, the radius of curvature at the lower end of the cross-sectional outer shape is smallest at the front end 22 and largest at the rear fuselage 24.

[0038] In the floating structure 2 shown in Figure 7A, the mooring point A1 is located on the front body 23 and is positioned forward of the midpoint of the overall length of the floating structure 2 in the longitudinal direction (actually, forward of the center of gravity of the floating structure 2). As previously described, the drag force D1 per unit length in the floating body 21 is minimum at the front end 22 and maximum at the rear body 24. Furthermore, a large drag force acts in the width direction in the extension section 26 as well. As a result, a rotational torque (see arrow T1 in Figure 7A) acts approximately centered near the mooring point A1, such that the front end 22 faces upstream in the flow direction F1 and the extension section 26 faces downstream in the flow direction F1. As shown in Figure 7B, even when the longitudinal direction of the floating structure 2 is inclined with respect to the flow direction F1, the rotational torque T1 acts in the same rotational direction as in Figure 7A.

[0039] As shown in Figure 7C, when the longitudinal direction of the floating structure 2 is approximately parallel to the flow direction F1 (i.e., when the floating structure 2 is directly facing the flow direction F1), there is almost no drag in the width direction at the extension section 26, the rear body 24, the front body 23, and the front end 22. As a result, the floating structure 2 maintains a state where it is directly facing the flow direction F1. When the floating structure 2 is directly facing the flow direction F1, the drag coefficient and projected area with respect to the flow direction F1 become smaller compared to the state in Figure 7A where the longitudinal direction is approximately perpendicular to the flow direction F1, and the longitudinal drag force acting on the floating structure 2 becomes smaller. As a result, the load acting on the mooring line 4 becomes smaller.

[0040] Here, we consider a comparative example floating structure. Figure 8 shows the comparative example floating structure 8. In the comparative example floating structure 8, the extended portion 26 in the floating structure 2 of Figure 5 is omitted. When the comparative example floating structure 8 is facing the flow direction F1, flow separation (fluid separation) occurs at the rear ends of each rear end side surface 812 of the rear end portion 81, and vortices are generated near the rear end surface 811. As a result, the drag force acting on the floating structure 8 (drag force directed towards the rear in the front-rear direction) becomes large. As shown by the dashed line in Figure 8, if a plate member 821 is provided in the center in the width direction of the rear end surface 811, it is possible to easily face the floating structure 8 directly with respect to the flow direction F1, but as in the above case, vortices are generated near the rear end surface 811, and the drag force acting on the floating structure 8 becomes large.

[0041] On the other hand, in the floating structure 2 of Figure 5, as previously described, the pair of extended surfaces 264 of the extended portion 26 extend continuously to the rear from both rear end sides 252 of the rear end portion 25, and move closer to each other as they move towards the rear. When the floating structure 2 is facing the flow direction F1, as shown by arrow F2 in Figure 7C, a flow is generated from the rear end of the rear end side 252 along the extended surface 264, thereby suppressing the occurrence of flow separation as seen in the comparative floating structure 8. As a result, the drag force acting on the floating structure 2 facing the flow direction F1 (drag force directed towards the rear in the longitudinal direction) is significantly reduced compared to the comparative floating structure 8.

[0042] As shown in Figure 3, when the floating structure 2 has two floating body parts 21, a mooring line 4 is connected to a mooring section 29 connecting the two floating body parts 21 (a mooring point A1 is provided), so the mooring line 4 is indirectly connected to each floating body part 21. In the floating structure 2 of Figure 3, the mooring line 4 is connected to the front of the center of the floating structure 2 in the longitudinal direction, and an extension section 26 is attached to the rear end 25 of each floating body part 21. In addition, in the floating body part 21, the drag force D1 per unit length is minimized at the front end 22 and maximized at the rear body 24. As a result, similar to the examples in Figures 7A to 7C, the floating structure 2 easily faces the flow direction F1. Furthermore, flow separation (more precisely, flow separation at the rear end of the rear end side surface 252) in the floating structure 2 when it is facing the flow direction F1 is suppressed, and the drag force acting on the floating structure 2 is reduced.

[0043] In practice, in the mooring system 1 shown in Figure 1, the floating structure 2 swings around the mooring base 3 (or the end of the mooring line 4 that is in contact with the seabed 92 and is opposite to the mooring base 3), and is positioned on the downstream side in the flow direction F1. The mooring line 4 extends from the seabed 92 along the flow direction F1. As previously described, the drag force acting on the floating structure 2 is reduced, so the load acting on the mooring line 4 is also reduced.

[0044] In the floating structure 2, the cross-sectional shape of the floating body 21 perpendicular to the front-rear direction may be constant throughout the entire front-rear direction. Even in this case, by attaching the extension portion 26 to the rear end portion 25 of the floating body 21 and by directly or indirectly connecting the mooring line 4 to a position forward of the center of the floating structure 2 in the front-rear direction, it is possible to easily orient the floating structure 2 directly toward the flow direction F1. In other words, it is possible to avoid a state in which the flow direction F1 is substantially parallel to the width direction of the floating structure 2 and a large load acts on the mooring line 4 for a long period of time. Furthermore, by having the extension portion 26 extend continuously to the rear from both sides (rear end sides) 252 of the rear end portion 25 and having a pair of extension surfaces 264 that move closer to each other as they move toward the rear, flow separation in the floating structure 2 when it is facing the flow direction F1 can be suppressed. This reduces the drag force acting on the floating structure 2 and the load acting on the mooring line 4, thereby preventing or suppressing damage (such as wear damage if it is a chain) or breakage of the mooring line 4. As a result, the mooring line 4 can be made smaller in diameter and lighter, thereby reducing the manufacturing cost of the mooring system 1.

[0045] Furthermore, the extension portion 26 has a water-filled space P between the pair of extension surfaces 264 into which water can enter. As a result, almost no buoyancy is generated in the extension portion 26, and the center of buoyancy of the floating structure 2 can be positioned towards the front of the floating structure 2 in the longitudinal direction (for example, forward of the center). Consequently, as described above, it is possible to prevent or suppress a large tilt in the pitch direction of the floating structure 2's posture (balance) while connecting the mooring line 4 forward of the center of the floating structure 2 in the longitudinal direction (while applying a downward force).

[0046] Preferably, the floating body 21 has a front end 22, a front fuselage 23, and a rear fuselage 24 along the longitudinal direction, with the rear end 25 being included in the rear fuselage 24. Furthermore, in the front end 22, front fuselage 23, and rear fuselage 24, the drag force per unit length in the longitudinal direction against the flow in the width direction is minimized at the front end 22 and maximized at the rear fuselage 24. This makes it easier to orient the floating structure 2 directly with respect to the flow direction F1. In the above case, by forming the front end 22 from foam, the center of gravity of the floating structure 2 can be positioned towards the rear, and the attitude of the floating structure 2 can be stabilized while connecting the mooring line 4 forward of the center of the floating structure 2.

[0047] Figures 9A to 9D show other examples of the floating structure 2. In Figures 9A to 9D, the only difference compared to the floating structure 2 in Figure 5 is the structure of the extension 26. In the extension 26 of Figure 9A, the extension 26 is formed by bending one plate member 261a into a roughly V-shape when viewed along the vertical direction. With the bend as the boundary, one side of the plate member 261a and the other side correspond to the two plate members 261 in Figure 5, respectively. The one plate member 261a and the rear end surface 251 of the rear end 25 in Figure 9A surround the four sides of the flooded space P. In the example of Figure 9A, a pair of extension surfaces 264 that extend continuously rearward from both rear end sides 252 of the rear end 25 are the surfaces of the two parts of the plate member 261a.

[0048] As shown in Figures 5 and 9A, the stretched portion 264 may be the surface of a pair of plate members 261, or the surface of a single plate member 261a. In other words, the pair of stretched surfaces 264 may be the surface of a pair of plate-like portions, thereby allowing the stretched portion 26 to be easily manufactured. Furthermore, as the pair of plate-like portions move closer to each other towards the rear and their rear ends connect, a stretched portion 26 with high resistance to deformation can be easily realized.

[0049] In the extended section 26 of Figure 9B, the rear ends of a pair of plate members 261 are separated from each other in the width direction, and an auxiliary plate member 266 is provided to connect these rear ends. The auxiliary plate member 266 extends in the width direction and the vertical direction. In Figure 9B, the two plate members 261, the auxiliary plate member 266, and the rear end surface 251 of the rear end section 25 surround the flooded space P on all four sides. In the extended section 26 of Figure 9C, two pairs of plate members 261 are arranged in the width direction, and the flooded space P is formed by each pair of plate members 261. In this way, a flooded space P surrounded on all four sides can be formed by various structures.

[0050] In the extended portion 26 of Figure 9D, the auxiliary plate member 266 in the extended portion 26 of Figure 9B is omitted, and the rear ends of the pair of plate members 261 are not connected directly or indirectly. Therefore, the rear side of the flooded space P is open. Even in this case, the pair of extended surfaces 264 that extend continuously to the rear from both rear end sides 252 of the rear end portion 25 can suppress flow separation at the rear end of the rear end sides 252, thereby reducing drag. On the other hand, in order to easily realize an extended portion 26 with high strength, it is preferable that the rear ends of the pair of plate members 261 are connected directly or indirectly, that is, that the flooded space P is a space enclosed on all four sides.

[0051] Figure 10 shows another example of the floating structure 2. In the floating structure 2 of Figure 10, the rear end surface 251 at the rear end 25 of the floating body 21 is a substantially spherical or ellipsoidal surface, or a substantially cylindrical surface. In other words, the corner portion 253 provided at the rear end 25 in Figure 5 is not provided. The extended surfaces 264 of the pair of plate members 261 extend rearward from near the boundary between the rear end side surface 252 and the rear end surface 251, and approach each other as they move towards the rear. Thus, the extended portion 26 may be attached to the rear end 25 where the corner portion 253 is not provided. In this case as well, the extended portion 26 makes it easy to orient the floating structure 2 directly toward the flow direction F1, while suppressing flow separation in the floating structure 2 when it is orienting directly toward the flow direction F1. On the other hand, in the floating body 21 where the corner portion 253 is formed at the rear end 25, flow separation becomes significant. Therefore, in a floating body 21 having corners 253, it is particularly preferable that a pair of extended surfaces 264 extend backward from both corners 253 by attaching an extended portion 26. This makes it possible to suppress flow separation caused by the corners 253.

[0052] The floating structure 2 described above is capable of various deformations.

[0053] In the floating structure 2 shown in Figure 2, a portion of the extension 26 is located above the waterline, but as shown in Figures 11A to 11C, substantially the entire extension 26 may be located below the waterline. Even in this case, the floating structure 2 can be easily oriented directly toward the flow direction, and flow separation in the floating structure 2 when it is oriented directly toward the flow direction can be suppressed, thereby reducing the drag force acting on the floating structure 2. As described above, it is preferable that the extension 26 be provided at least below the waterline.

[0054] When viewed along the width direction, in the example of Figure 11A, the upper and lower ends of each plate member 261 are approximately parallel in the front-rear direction. In the example of Figure 11B, the upper end of each plate member 261 is approximately parallel in the front-rear direction, and the lower end approaches the upper end as it moves towards the rear. In the example of Figure 11C, the upper end is located lower as it moves towards the rear, and the lower end is located higher as it moves towards the rear. In the examples of Figures 11A to 11C, the lower part of the flooded space P may be closed, and only the top may be open. Even in this case, water will enter the flooded space P, so a large buoyancy is prevented from being generated in the extended portion 26. As described above, when the flooded space P is enclosed on all four sides, it is preferable that the flooded space P is a space that is open at the top and / or bottom.

[0055] The extended portion 26 does not necessarily have to be formed from plate members 261, 261a. For example, a triangular prism extending in the vertical direction, with through holes extending in the vertical direction (through holes that become water-filled spaces P), may be used as the extended portion 26.

[0056] The shapes of the front end 22, front fuselage 23, and rear fuselage 24 can be varied. For example, as shown in Figure 12, the front end 22 may have a constant cross-sectional shape in the front-rear direction. Also, in the front fuselage 23 and front end 22, the lower end of the cross-sectional shape perpendicular to the front-rear direction may be V-shaped, polygonal, or otherwise not rounded. The drag force per unit length in the front end 22, front fuselage 23, and rear fuselage 24 may be changed by changing the size of the cross-section perpendicular to the front-rear direction or the coefficient of friction of the surface.

[0057] The configurations in the above embodiments and each modified example may be combined as appropriate, as long as they do not contradict each other. [Explanation of Symbols]

[0058] 2. Floating structures 4. Mooring lines 21 Floating body 22 Front end 23 Forward fuselage 24 Rear fuselage 25 Rear end 26 Extension 251 Backend 252 Rear Side 253 corner 261, 261a Plate Material 264 Extended surface P Immersion Space

Claims

1. A floating structure moored by a mooring line, A floating body extending in the front-to-back direction, to which mooring lines are directly or indirectly connected, An extension portion is attached to the rear end of the floating body in the front-rear direction, and extends continuously to the rear from both sides of the rear end, having a pair of extending surfaces that move closer to each other as they move towards the rear, Equipped with, The extended portion has a water-filled space between the pair of extended surfaces into which water can enter. A floating structure to which the mooring line is connected, located forward of the center of the floating structure in the aforementioned front-to-back direction.

2. A floating structure according to claim 1, A floating structure in which the flooded space is enclosed on all four sides and has openings at the top and / or bottom.

3. A floating structure according to claim 1, A floating structure in which the pair of extended surfaces are the surfaces of a pair of plate-like portions.

4. A floating structure according to claim 3, A floating structure in which the pair of plate-like portions move closer to each other as they extend towards the rear, and their rear ends connect.

5. A floating structure according to claim 1, The rear end of the floating body has an end face that forms a corner together with each of the two side faces, Each of the pair of extended surfaces is a floating structure that extends rearward from the corner.

6. A floating structure according to any one of claims 1 to 5, The floating body has a front end, a front fuselage, and a rear fuselage along the front-rear direction, and the rear end is included in the rear fuselage. A floating structure in which, in the front end, the front fuselage, and the rear fuselage, the drag per unit length in the longitudinal direction against a flow in the width direction perpendicular to the longitudinal and vertical directions is minimized at the front end and maximized at the rear fuselage.

7. A floating structure according to claim 6, A floating structure whose front end is formed of foam.

Images