Vibration reduction anchoring structure of suction anchor and optimization and implementation method of vibration reduction anchoring structure

Abstract

The invention discloses a vibration reduction anchoring structure of a suction anchor and an optimization and implementation method thereof.The vibration reduction anchoring structure is installed on the outer wall of the suction anchor of a semi-submersible platform, when an anchor chain is stretched, a force bearing column moves and compresses an annular spring, and the effect of absorbing horizontal loads is achieved; according to the optimization method of the vibration reduction anchoring structure, the optimal angle of the mooring point anchor chain is determined through iteration, dynamic load transmission is restrained, and it is guaranteed that the bearing performance of the suction anchor reaches the optimal state; according to the implementation method of the vibration reduction anchoring structure, the vibration reduction anchoring structure is installed according to the optimal angle, and after installation is completed, cement paste is injected into a soil body above the anchor chain, so that a compact soil layer is formed on the upper portion of the anchor chain, and the optimal angle of the anchor chain is maintained. The service life of the suction anchor can be remarkably prolonged, and the operation and maintenance cost of the deep-sea platform is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the anchoring system of offshore foundation engineering, in particular to a damping anchoring structure of suction anchor and its optimization and implementation method. BACKGROUND

[0002] Suction anchor is one of the anchoring foundations of floating platform, such as semi-submersible platform. At the anchoring position of suction anchor, the anchor chain is usually directly connected with the ring structure on the suction anchor. Under the action of dynamic load such as wave and ocean current, the periodic tension of the anchor chain will cause the increase of pore water pressure and the degradation of shear stiffness of soil at the anchor-soil interface, thereby reducing the uplift capacity of the suction anchor. The existing anchoring structure of suction anchor cannot effectively isolate the transmission of dynamic load to the soil. SUMMARY

[0003] The first object of the present application is to provide a damping anchoring structure of suction anchor capable of inhibiting the transmission of dynamic load to the soil; the second object of the present application is to provide an optimization method of the damping anchoring structure to determine the optimal angle between the anchor chain and the suction anchor; and the third object of the present application is to provide an implementation method of the damping anchoring structure.

[0004] Technical solution: The damping anchoring structure of suction anchor of the present application comprises a ring spring, a spring base, a flange plate, an outer shell fixed on the flange plate, and a load-bearing column slidingly arranged in the outer shell, wherein the outer side end of the load-bearing column is provided with a ring of protrusions for axial limiting, the spring base is arranged inside the outer shell and fixedly connected with the inner side end of the load-bearing column, the ring spring is sleeved on the load-bearing column, and the two ends of the ring spring are fixedly connected with the spring base and the outer shell respectively; a universal joint is fixed on the outer side end of the load-bearing column, the anchor chain is connected with the universal joint, and the flange plate is used for fixing the damping anchoring structure on the side surface of the suction anchor.

[0005] Further, the load-bearing column and the outer shell are made of titanium alloy material, and the ring spring is made of Hastelloy C276 material.

[0006] Further, the distance between the installation position of the flange plate and the anchor bottom of the suction anchor accounts for 1 / 3 to 1 / 2 of the length of the suction anchor.

[0007] Further, the flange plate is welded to the outer wall of the suction anchor of the semi-submersible platform.

[0008] Further, the surfaces of the load-bearing column, the ring spring and the outer shell are sprayed with phenolic epoxy paint coating to prevent seawater corrosion.

[0009] The optimization method of the damping anchoring structure of suction anchor of the present application comprises:

[0010] (1) Parameter configuration of the suction anchor and soil layer is performed, the initial value of the angle α between the anchor chain and the suction anchor, the value range of the angle α, and the initial value of the ultimate anchor tension T are set, and the suction anchor foundation is divided into several foundation units from top to bottom;

[0011] (2) Calculate the ultimate bearing capacity of the suction anchor foundation;

[0012] (2.1) Value of soil resistance in elastic state;

[0013] Each foundation unit includes three types of distributed springs, namely horizontal soil resistance spring, vertical soil resistance spring and additional moment spring. The horizontal soil resistance spring is described by the py curve, where p is the horizontal soil resistance per unit length and y is the horizontal displacement of the suction anchor; the vertical soil resistance spring is described by the τ-z curve, where τ is the vertical soil resistance per unit length and z is the vertical displacement of the suction anchor; the additional moment spring is described by the m-θ curve, where m is the additional moment per unit length and θ is the cross-sectional rotation angle of the suction anchor.

[0014] (2.2) Perform suction anchor-soil interaction calculations. The calculation method lists the governing equations for each foundation unit based on the principle of mechanical equilibrium, solves the unknowns based on the continuity conditions of the discretized mechanical model of the suction anchor, and outputs the initial response values ​​of the foundation unit in the soil. The response values ​​include the horizontal displacement y of the suction anchor, the vertical displacement z of the suction anchor, and the cross-sectional rotation angle θ of the suction anchor.

[0015] (2.3) Substitute the initial response values ​​into the three distributed springs to obtain the new soil resistance value, then return to step (2.2) and use the new soil resistance value to calculate the new response value of the foundation unit in the soil; the soil resistance value includes the horizontal soil resistance per unit length p, the vertical soil resistance per unit length τ, and the additional moment per unit length m;

[0016] (2.4) Obtain the new value y of the maximum horizontal displacement of the suction anchor new and the initial value of the maximum horizontal displacement of the suction anchor y old The absolute value of the error e y , the new value of the maximum vertical displacement of the suction anchor z new and the initial value of the maximum vertical displacement of the suction anchor z old The absolute value of the error e z And the new value of the maximum cross-sectional rotation angle of the suction anchor θ new and the initial value of the maximum cross-sectional rotation angle of the suction anchor θ old The absolute value of the error e θ , judge e y 、e z and e θ Whether the judgment criteria are met, if so, proceed to step (2.5); if not, update the initial response value to the new response value of the foundation unit in the soil and return to step (2.3);

[0017] (2.5) storing the T value, the corresponding basic response and the anchor displacement value s obtained in step (2.4), the basic response including the response new value of each basic unit and the corresponding soil resistance new value;

[0018] The calculation formula of s is:

[0019]

[0020] Wherein, y k is the horizontal displacement y of the basic unit at the stress point; z k is the vertical displacement z of the basic unit at the stress point;

[0021] (2.6) judging whether s is greater than the set standard, if yes, entering step (3); if not, executing T=T+ΔT and returning to step (2.1), ΔT is the loop step of T;

[0022] (3) storing the T value and the corresponding basic response and s value in step (2);

[0023] (4) finding the minimum value of s in step (3);

[0024] (5) judging whether the minimum value of s in step (4) is the minimum value of the entire value range of angle α, if yes, outputting the basic response and the corresponding α value and T value; if not, executing α=α+Δα and returning to step (2.1), Δα is the loop step of α.

[0025] Further, the value range of angle α is 10°-80°.

[0026] Further, the judgment standard of e y , e z and e θ is to satisfy the following three formulas at the same time:

[0027]

[0028] Further, the set standard of s is 0.08-0.12 times the diameter or side length of the suction anchor.

[0029] The implementation method of the vibration reduction anchoring structure of the suction anchor described in the application comprises:

[0030] (1) determining the optimal angle between the anchor chain and the suction anchor through the optimization method of the vibration reduction anchoring structure of the suction anchor;

[0031] (2) cleaning the scour depression area of the seabed around the suction anchor, backfilling and leveling with graded sand or underwater concrete, and ensuring the stability of the seabed foundation;

[0032] (3) using a crane to hoist the suction anchor above the predetermined installation position, then adjusting the horizontal and vertical directions, accurately positioning, allowing the suction anchor to sink by gravity; when the suction anchor sinks to a certain depth, send an underwater robot or a diver to install the damping anchor structure on the side of the suction anchor through the flange, and connect the end of the anchor chain with the universal joint;

[0033] (4) further sinking the suction anchor to the design depth;

[0034] (5) tensioning the anchor chain to the optimal angle and injecting cement slurry into the soil above the anchor chain to form a dense soil layer at the upper part of the anchor chain to maintain the optimal angle of the anchor chain.

[0035] Beneficial effects: compared with the prior art, the present application has the following significant advantages: the damping anchor structure effectively alleviates the adverse effects of micro-amplitude load on the soil; the optimal angle between the anchor chain and the suction anchor is obtained through iteration, thereby optimizing the installation position of the damping anchor structure on the suction anchor of the semi-submersible platform, which suppresses the transmission of dynamic load and ensures that the bearing performance of the suction anchor is in the best state. The present application can significantly prolong the service life of the suction anchor and reduce the operation and maintenance cost of the deep-sea platform. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a damping anchor structure of a suction anchor provided by an embodiment of the present application;

[0037] Figure 2 is a schematic view of the damping anchor structure installed on the suction anchor of the semi-submersible platform in an embodiment of the present application;

[0038] Figure 3 is a schematic view of the optimal angle between the anchor chain and the suction anchor in an embodiment of the present application;

[0039] Figure 4 is a mechanical model of various soil resistances borne by the suction anchor in an embodiment of the present application;

[0040] Figure 5 is a flowchart of an optimization method of a damping anchor structure of a suction anchor in an embodiment of the present application. DETAILED DESCRIPTION

[0041] The present application will be further described below with reference to the accompanying drawings.

[0042] The accompanying drawings in Figures 1 to 5 The reference signs in the accompanying drawings are as follows:

[0043] 1, suction anchor; 2, damping anchor structure; 21, load-bearing column; 22, ring spring; 23, outer shell; 24, spring base; 3, flange; 4, universal joint; 5, anchor chain.

[0044] Embodiment 1

[0045] As shown in Figure 1 and Figure 2 , embodiment 1 provides a vibration-damping anchoring structure of a suction anchor, which is installed on the outer wall of a suction anchor 1 of a semi-submersible platform and comprises a flange plate 3, a load-bearing column 21, an annular spring 22, an outer shell 23 and a spring base 24, wherein the outer shell 23 is welded and fixed on the flange plate 3, the load-bearing column 21 is slidingly arranged on the outer shell 23, and the outer side end of the load-bearing column 21 is provided with a ring of protrusions, which functions as an axial limiting part. The spring base 24 is arranged inside the outer shell 23, and the inner side end of the load-bearing column 21 is fixed on the spring base 24. The annular spring 22 is sleeved on the load-bearing column 21, and the two ends of the annular spring 22 are fixedly connected with the spring base 24 and the outer shell 23, respectively. The outer side end of the load-bearing column 21 is fixed with a universal joint 4, and an anchor chain 5 is connected with the universal joint 4. The flange plate 3 is welded and fixed on the outer wall of the suction anchor 1 of the semi-submersible platform, and the installation position is at a distance of 1 / 3 to 1 / 2 of the length of the suction anchor 1 from the anchor bottom.

[0046] In this embodiment, the load-bearing column 21 is made of high-strength corrosion-resistant titanium alloy material, the annular spring 22 is made of Hastelloy C276 material, and the outer shell 23 has a wall thickness of 50 mm and is made of titanium alloy material. In addition, the surfaces of the load-bearing column 21, the annular spring 22 and the outer shell 23 are sprayed with a phenolic epoxy paint coating to prevent seawater corrosion.

[0047] The working principle of the vibration-damping anchoring structure is as follows: when the anchor chain 5 is stretched, the load-bearing column 21 moves and compresses the annular spring 22, thereby achieving the effect of absorbing horizontal load and making the vibration-damping anchoring structure have a vibration-damping function. The present application can significantly prolong the service life of the suction anchor and reduce the operation and maintenance cost of the deep-sea platform.

[0048] Embodiment 2

[0049] As shown in Figures 3 to 5 , embodiment 2 provides an optimization method of a vibration-damping anchoring structure of a suction anchor, which comprises the following steps:

[0050] (1) configuring parameters for the suction anchor 1 and the soil layer, setting the initial value of the angle a between the anchor chain 5 and the suction anchor 1, the value range of the angle a and the initial value of the ultimate anchor tension T, dividing the suction anchor foundation from top to bottom into n+1 foundation units and numbering them in sequence as 0-n;

[0051] The suction anchor parameters include the geometric parameters of the suction anchor, the material mechanics parameters (elastic modulus, Poisson's ratio, yield strength) of the material, the structural parameters (the position height of the anchoring point); the soil layer parameters include the physical property parameters (specific gravity, water content, pore ratio) of the soil, the mechanics property parameters (shear strength parameter, elastic modulus, Poisson's ratio, stiffness coefficient, ultimate bearing capacity coefficient) of the soil, and the thickness of the soil layer. The value range of the angle a is 10°-80°, and the initial value of the ultimate anchor tension T is 40000kN.

[0052] (2) calculating the ultimate bearing capacity of the suction anchor foundation;

[0053] (2.1) the value of the soil resistance in the elastic state;

[0054] The various soil resistances borne by the suction anchor are calculated by using the mechanical model shown in the figure, Figure 3 Figure 4 Each foundation unit includes three kinds of distributed springs, which are horizontal soil resistance spring, vertical soil resistance spring and additional torque spring. The horizontal soil resistance spring is described by p-y curve, wherein p is the unit length horizontal soil resistance, and y is the horizontal displacement of the suction anchor; the vertical soil resistance spring is described by τ-z curve, wherein τ is the unit length vertical soil resistance, and z is the vertical displacement of the suction anchor; the additional torque spring is described by m-θ curve, wherein m is the unit length additional torque, and θ is the section angle of the suction anchor;

[0055] (2.2) the calculation of the interaction between the suction anchor and the soil is carried out, the control equation of each foundation unit is listed according to the principle of mechanical equilibrium, the unknown quantity is solved by combining the continuity condition of the discrete mechanical model of the suction anchor, and the initial value of the response of the foundation unit in the soil is output; the response value includes the horizontal displacement y of the suction anchor, the vertical displacement z of the suction anchor and the section angle θ of the suction anchor;

[0056] (2.3) the response initial value is brought into the three kinds of distributed springs to obtain the new value of the soil resistance, and then the step (2.2) is returned to obtain the new value of the response of the foundation unit in the soil by using the new value of the soil resistance; the soil resistance value includes the unit length horizontal soil resistance p, the unit length vertical soil resistance τ and the unit length additional torque m;

[0057] (2.4) the error absolute value e new of the new value y old of the maximum horizontal displacement of the suction anchor and the initial value y y of the maximum horizontal displacement of the suction anchor, the error absolute value e new of the new value z old of the maximum vertical displacement of the suction anchor and the initial value z z of the maximum vertical displacement of the suction anchor, and the error absolute value e new of the new value θ old of the maximum section angle of the suction anchor and the initial value θ of the maximum section angle of the suction anchor are obtained.absolute value of the error e θ determining whether e y , e z and e θ meet the determination criteria, the determination criteria of e y , e z and e θ are that the following three formulas are met simultaneously:

[0058]

[0059] If yes, go to step (2.5); if no, update the response initial value to the response new value of the foundation unit in the soil and return to step (2.3);

[0060] (2.5) store the T value, the corresponding foundation response and the anchor tension displacement value s obtained in step (2.4), the foundation response including the response new value of each foundation unit and the corresponding soil resistance new value;

[0061] The calculation formula of s is:

[0062]

[0063] wherein y k is the horizontal displacement y of the foundation unit at the force point; and z k is the vertical displacement z of the foundation unit at the force point;

[0064] (2.6) determine whether s is greater than the set standard, the set standard being 0.08-0.12 times the diameter or side length of the suction anchor. If yes, go to step (3); if no, execute T=T+ΔT and return to step (2.1), ΔT being the loop step of T, ΔT being 100 kN;

[0065] (3) store the T value and the corresponding foundation response and s value in step (2);

[0066] (4) find the minimum value of s in step (3);

[0067] (5) determine whether the minimum value of s in step (4) is the minimum value in the entire value range of the angle α, if yes, output the foundation response and the corresponding α value and T value; if no, execute α=α+Δα and return to step (2.1), Δα being the loop step of α, Δα being 0.5°.

[0068] The optimization method determines the optimal angle of the mooring point anchor chain through iteration, suppresses the dynamic load transmission, and ensures that the bearing performance of the suction anchor is in the best state.

[0069] Example 3

[0070] Embodiment 3 provides an implementation method of the shock-absorbing anchoring structure of the suction anchor, comprising the following steps:

[0071] (1) Determine the optimal angle between the anchor chain 5 and the suction anchor 1 by the optimization method of the shock-absorbing anchoring structure of the suction anchor described in Embodiment 2;

[0072] (2) Clean up the scour depression area of the seabed around the suction anchor 1, backfill and level with graded sand or underwater concrete, and ensure the stability of the seabed foundation;

[0073] (3) Use the crane ship to hoist the suction anchor 1 above the predetermined installation position, then adjust the horizontal and vertical directions, accurately position, and let the suction anchor 1 sink by gravity; when the suction anchor 1 sinks to a certain depth, send the underwater robot or the diver to install the shock-absorbing anchoring structure on the side of the suction anchor 1 through the flange 3, and connect the end of the anchor chain 5 with the universal joint 4;

[0074] (4) Make the suction anchor 1 sink further to the designed depth;

[0075] (5) Stretch the anchor chain 5 to the optimal angle and inject cement slurry into the soil above the anchor chain 5, so as to form a dense soil layer on the upper part of the anchor chain 5 to maintain the optimal angle of the anchor chain 5.

Claims

1. A vibration-damping anchoring structure of a suction anchor, characterized in that: The invention comprises an annular spring (22), a spring base (24), a flange (3), a shell (23) fixed on the flange (3), and a bearing column (21) slidably arranged on the shell (23); the outer end of the bearing column (21) has a circle of protrusions for axial limiting; the spring base (24) is arranged inside the shell (23) and is fixedly connected to the inner end of the bearing column (21); the annular spring (22) is sleeved on the bearing column (21); the two ends of the annular spring (22) are respectively fixedly connected to the spring base (24) and the shell (23); a universal joint (4) is fixed to the outer end of the bearing column (21); an anchor chain (5) is connected to the universal joint (4); and the flange (3) is used to fix the vibration-damping anchoring structure to the side of the suction anchor (1).

2. The vibration-damping anchoring structure according to claim 1, characterized in that: The bearing column (21) and the housing (23) are made of titanium alloy, and the annular spring (22) is made of Hastelloy C276.

3. The vibration-damping anchoring structure according to claim 1, characterized in that: The distance between the installation position of the flange (3) and the anchor bottom of the suction anchor (1) is 1 / 3 to 1 / 2 of the length of the suction anchor (1).

4. The vibration-damping anchoring structure according to claim 3, characterized in that: The flange (3) is welded to the outer wall of the suction anchor (1) of the semi-submersible platform.

5. The vibration-damping anchoring structure according to claim 1, characterized in that: The surfaces of the load-bearing column (21), the annular spring (22) and the housing (23) are sprayed with a phenolic epoxy paint coating to prevent seawater corrosion.

6. A method for optimizing the vibration-damping anchoring structure of a suction anchor according to claim 1, characterized in that: include: (1) Parameter configuration is performed on the suction anchor (1) and the soil layer, an initial value of the angle α between the anchor chain (5) and the suction anchor (1), a value range of the angle α, and an initial value of the ultimate anchor tension T are set, and the suction anchor foundation is divided into a plurality of foundation units from top to bottom; (2) Calculate the ultimate bearing capacity of the suction anchor foundation; (2.1) Value of soil resistance in elastic state; Each foundation unit includes three types of distributed springs, namely horizontal soil resistance spring, vertical soil resistance spring and additional moment spring. The horizontal soil resistance spring is described by the py curve, where p is the horizontal soil resistance per unit length and y is the horizontal displacement of the suction anchor; the vertical soil resistance spring is described by the τ-z curve, where τ is the vertical soil resistance per unit length and z is the vertical displacement of the suction anchor; the additional moment spring is described by the m-θ curve, where m is the additional moment per unit length and θ is the cross-sectional rotation angle of the suction anchor. (2.2) Perform suction anchor-soil interaction calculations. The calculation method lists the governing equations for each foundation unit based on the principle of mechanical equilibrium, solves the unknowns based on the continuity conditions of the discretized mechanical model of the suction anchor, and outputs the initial response values ​​of the foundation unit in the soil. The response values ​​include the horizontal displacement y of the suction anchor, the vertical displacement z of the suction anchor, and the cross-sectional rotation angle θ of the suction anchor. (2.3) Substitute the initial response values ​​into the three distributed springs to obtain the new soil resistance value, then return to step (2.2) and use the new soil resistance value to calculate the new response value of the foundation unit in the soil; the soil resistance value includes the horizontal soil resistance per unit length p, the vertical soil resistance per unit length τ, and the additional moment per unit length m; (2.4) Obtain the new value y of the maximum horizontal displacement of the suction anchor new and the initial value of the maximum horizontal displacement of the suction anchor y old The absolute value of the error e y , the new value of the maximum vertical displacement of the suction anchor z new and the initial value of the maximum vertical displacement of the suction anchor z old The absolute value of the error e z And the new value of the maximum cross-sectional rotation angle of the suction anchor θ new and the initial value of the maximum cross-sectional rotation angle of the suction anchor θ old The absolute value of the error e θ , judge e y 、e z and e θ Whether the judgment criteria are met, if so, proceed to step (2.5); if not, update the initial response value to the new response value of the foundation unit in the soil and return to step (2.3); (2.5) Store the T value, the corresponding foundation response, and the anchorage displacement value s obtained in step (2.4). The foundation response includes the new response value of each foundation unit and the corresponding new soil resistance value. The calculation formula for s is: Among them, y k is the horizontal displacement y of the foundation unit at the force point; z k is the vertical displacement z of the foundation unit at the force point; (2.6) Determine whether s is greater than the set standard. If so, proceed to step (3); if not, execute T = T + ΔT and return to step (2.1), where ΔT is the loop step length of T; (3) storing the T value and the corresponding basic response and s value in step (2); (4) Find the minimum value of s in step (3); (5) Determine whether the minimum value of s in step (4) is the minimum value of the entire value range of angle α. If so, output the basic response and the corresponding α value and T value; if not, execute α = α + Δα and return to step (2.1), where Δα is the loop step size of α.

7. The method for optimizing the vibration-damping anchoring structure of a suction anchor according to claim 6, characterized in that: The value range of the angle α is 10° to 80°.

8. The method for optimizing the vibration-damping anchoring structure of a suction anchor according to claim 6, characterized in that: e y 、e z and e θ The judgment criteria are to satisfy the following three formulas at the same time:

9. The method for optimizing the vibration-damping anchoring structure of a suction anchor according to claim 6, characterized in that: The setting standard of s is 0.08 to 0.12 times the diameter or side length of the suction anchor.

10. A method for implementing a vibration-damping anchoring structure of a suction anchor, characterized in that: include: (1) Determining the optimal angle between the anchor chain (5) and the suction anchor (1) by using the optimization method for the vibration-damping anchoring structure of the suction anchor according to any one of claims 6 to 9; (2) Clean the scour depression area of ​​the seabed around the suction anchor (1), backfill and level it with graded sand and gravel or underwater concrete to ensure the stability of the seabed base; (3) using a crane to lift the suction anchor (1) to the top of the predetermined installation position, then adjusting the horizontal and vertical directions, accurately positioning, and allowing the suction anchor (1) to sink by its own weight; after the suction anchor (1) sinks to a certain depth, dispatching an underwater robot or a diver to install the vibration-damping anchoring structure on the side of the suction anchor (1) through the flange (3), and connecting the end of the anchor chain (5) to the universal joint (4); (4) further sinking the suction anchor (1) to the designed depth; (5) tensioning the anchor chain (5) to an optimal angle and injecting cement slurry into the soil above the anchor chain (5) to form a dense soil layer above the anchor chain (5) to maintain the optimal angle of the anchor chain (5).

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