Offshore installation method for pile foundation jacket of ultra-large converter station

Abstract

The invention provides an offshore installation method for an ultra-large converter station pile foundation jacket, and relates to the technical field of offshore heavy structure installation. Comprising the steps that a floating crane ship, a semi-submersible barge and a jacket in an ultra-large converter station pile foundation hoisting scene serve as a core multi-floating-body system, and a'hydrodynamic parameter-motion response-load distribution 'linkage control logic is established through seabed refined detection and sea condition window quantitative screening in combination with hydrodynamic interference analysis in a double-ship typical arrangement form; by means of the multi-floating-body coupling hydrodynamic model, collaborative matching of semi-submersible barge diving, floating crane ship hoisting loading and multi-floating-body motion response is achieved, the technical problems that according to a traditional installation method, due to the fact that multi-floating-body hydrodynamic interference is ignored, the collaboration is poor, and the safety risk is high are solved, and the method is suitable for offshore installation operation of the ultra-large converter station pile foundation jacket.

Description

Technical Field

[0001] This invention relates to the field of marine heavy structure installation technology, specifically a method for marine installation of a pile foundation jacket for an ultra-large converter station. Background Technology

[0002] With the large-scale development of offshore flexible DC transmission projects, the jacket foundation of ultra-large converter stations, as the core load-bearing structure of the project, relies on the coordinated operation of multiple floating bodies, including floating cranes and semi-submersible barges, for its offshore installation. Existing offshore installation technology for jacket foundations has significant limitations.

[0003] Ignoring the hydrodynamic interference effects of multi-buoy vessels: Existing technologies mostly conduct hydrodynamic calculations based on the isolated condition of a single floating body, without considering the wave-making interference and flow field interaction between floating crane vessels and semi-submersible barges in series or T-shaped arrangements. When the distance between the two vessels is 30-50m, wave-making interference can cause the prediction error of the single vessel's motion response to exceed 20%, and existing technologies do not quantify this interference, which can easily lead to jacket collisions or abnormal stress on the slings.

[0004] Lack of quantitative correlation between coupled response and operation: Existing technologies mostly rely on empirical operation control for the submersible barge's descent and the floating crane's loading, without establishing a linkage mechanism of "added mass - radiation damping - motion response". For example, without combining the peak pitch (RAO) of the two vessels to optimize the loading timing, the force fluctuation of the slings exceeds 15%, which cannot meet the installation accuracy requirements of the jacket foundation of ultra-large converter stations.

[0005] Sea state adaptation lacks theoretical support: Existing technologies mostly use fixed wave height and wind speed thresholds to select operating windows, without combining the logic of "measured sea state in the sea area + RAO calculation for multi-buoy vessels". For example, the impact of the difference between normal and strong wave directions in the installation area on the interference of the two vessels is not considered, resulting in low utilization of the operating window period, and there is no way to avoid the danger caused by gap resonance (wave number kL=nπ).

[0006] Load calculation is detached from hydrodynamic parameters: Existing technologies simplify load distribution to "total weight - buoyancy" without considering the impact of the added mass of both vessels and radiation damping on load transfer. For example, when a semi-submersible barge submerges to its maximum depth, changes in added mass can cause a real-time load calculation deviation of 100-200t, which can easily lead to single-vessel overload or sudden load drop.

[0007] In summary, existing technologies present technical challenges such as high coordination difficulty and high safety risks due to interference from the movement of multiple floating bodies during the installation of ultra-large structures. Summary of the Invention

[0008] Therefore, this invention provides a method for offshore installation of jacket foundations for ultra-large converter stations to solve the above problems. This method is based on the coupling response characteristics of multi-floating bodies and achieves three core objectives: quantifying the coupling response of the floating crane vessel-semi-submersible barge-jacket multi-floating body system and clarifying the hydrodynamic interference law under a typical dual-vessel arrangement; establishing a linkage mechanism of "hydrodynamic parameters-operational operation-load distribution" to improve the collaborative stability of multi-floating bodies; and optimizing sea state screening based on the motion characteristics of multi-floating bodies to improve the adaptability of the operation window and the safety of installation.

[0009] The present invention provides a method for offshore installation of a pile foundation jacket for an ultra-large converter station, which mainly includes the following steps:

[0010] S1: Use multibeam echo sounding equipment to scan the seabed in the jacket installation area, combine it with the sea state statistics of the installation area, and use frequency domain hydrodynamic calculation methods to obtain the response amplitude operator (RAO) of the multi-floating body system (including floating crane, semi-submersible vessel and jacket) to screen suitable operating windows.

[0011] S2: A semi-submersible barge carries the pre-assembled buoys of the ultra-large converter station pile foundation jacket to the construction sea area, and the barge is fixed in position by dropping a fixed anchor.

[0012] S3: The floating crane enters the construction sea area and is aligned with the semi-submersible barge in a series or T-shaped arrangement to ensure the span conditions required for the lifting operation.

[0013] S4: Install rigging and wave compensation devices between the floating crane vessel and the jacket, install collision protection components, and deploy multi-buoy monitoring equipment to collect real-time data on the relative position of the two vessels, the motion status of the floating bodies, and the stress data of the rigging.

[0014] S5: Untie the sea lashings between the jacket and the semi-submersible barge, and check the buoy sealing performance and the baseline status of the coupling response of the multi-buoy system;

[0015] S6: Calculate the added mass and radiation damping of the dual-ship system based on the frequency domain hydrodynamic model, derive the structural buoyancy by combining the jacket's water entry depth, and substitute it into the load linkage logic formula (real-time load of semi-submersible barge = total weight of jacket and pontoon - total buoyancy of jacket - real-time lifting weight of floating crane), and coordinate the submersion of the semi-submersible barge and the loading of the floating crane until the jacket is completely detached from the semi-submersible barge;

[0016] S7: The floating crane vessel lifts the jacket to the installation position, fine-tunes the attitude of the jacket through the attitude adjustment component, and removes the equipment after the jacket is fixed; among them, the multi-floating body system coupling response control is based on the dual-ship coupled hydrodynamic model based on the surface element method to avoid the risk of motion amplification caused by the resonance phenomenon between the two ships.

[0017] Furthermore, the operation window selection in step S1 needs to take into account the wind, wave, and current characteristics of the installation sea area and the motion threshold of the multi-buoy system. Through RAO analysis, sea conditions that are prone to resonance should be avoided to ensure that the motion state of the floating body meets the requirements of the installation operation.

[0018] Furthermore, the arrangement of the two ships in step S3 needs to be selected based on hydrodynamic interference analysis: the tandem arrangement is suitable for sea conditions where the wave direction is consistent with the long axis of the hull, so as to reduce hydrodynamic interference in the sway direction; the T-shaped arrangement is suitable for sea conditions with transverse or oblique waves, so as to optimize the stability of the roll direction.

[0019] Furthermore, the multi-buoy monitoring equipment in step S4 includes a GNSS positioner, a six-degree-of-freedom attitude sensor, and a sling tension sensor. The equipment data update frequency must meet the real-time control requirements to ensure timely feedback on the relative motion status of the two ships. When the relative motion amplitude exceeds the preset range, an adjustment mechanism is triggered.

[0020] Furthermore, the buoyancy of the jacket structure in step S6 needs to be obtained by combining the jacket's water entry depth and its own buoyancy characteristics. The total buoyancy is the sum of the structural buoyancy and the buoyancy of the pontoon. The load linkage logic needs to synchronously link the effects of the additional mass of the two ships and the radiation damping on the load transfer.

[0021] Furthermore, in step S6, the submersible barge's diving rate and the floating crane's loading rate need to be dynamically adjusted based on the relative motion of the two vessels. The diving rate should be controlled at 0.3-0.5 m / min, and the loading rate at 30-50 t / min, to ensure the stability of the multi-buoy system.

[0022] The present invention has the following advantages over the prior art:

[0023] 1. This invention provides a method for offshore installation of a jacket foundation for an ultra-large converter station, which quantifies the coupling response of a multi-floating body system consisting of a floating crane vessel, a semi-submersible barge, and the jacket foundation, and clarifies the hydrodynamic interference patterns under a typical dual-vessel arrangement; establishes a linkage mechanism of "hydrodynamic parameters - operation - load distribution" to improve the collaborative stability of the multi-floating bodies; and optimizes sea state screening based on the motion characteristics of the multi-floating bodies to improve the adaptability of the operation window and the safety of installation.

[0024] 2. This invention provides a method for offshore installation of a jacket foundation for an ultra-large converter station, featuring controllable multi-buoy interference: quantifying hydrodynamic interference from dual-ship deployment reduces motion response prediction error from 20% to less than 5%, mitigating resonance risk; intelligent collaborative control: establishing a "hydrodynamic-operation-load" linkage mechanism, ensuring relative motion between the two ships is ≤50mm; precise sea state adaptation: combining sea conditions with multi-buoy RAO screening windows extends the operational window by 20%; and precise load allocation: load calculation is correlated with hydrodynamic parameters, with G-submersible error ≤5%, avoiding single-ship overload. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the guide frame installation.

[0027] Figure 2 This is a schematic diagram of the pontoon installation.

[0028] Figure 3 This is a diagram showing the relationship between the lifting weight, radius, and lifting height of the crane vessel.

[0029] Figure 4 This is a schematic diagram of the pile positions during the installation of the jacket.

[0030] Figure 5 This is a flowchart of the installation process for the jacket foundation piles.

[0031] Figure 6 This is a schematic diagram showing the installation location of the jacket support. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment provides a method for offshore installation of a pile foundation jacket for an ultra-large converter station, mainly including the following steps:

[0035] S1: Use multibeam echo sounding equipment to scan the seabed in the jacket installation area, combine it with the sea state statistics of the installation area, and obtain the response amplitude operator (RAO) of the multi-floating body system through frequency domain hydrodynamic calculation method to select a suitable operating window;

[0036] Detailed seabed survey: A multibeam echo sounder (0.1m resolution) is used to scan a 200m×200m area of ​​the installation site to identify protruding obstacles (those with a height > 0.3m need to be cleared by underwater blasting) to ensure that the seabed flatness error is ≤ 0.3m; Simultaneously, seabed sediment (silt thickness, bearing capacity) data are collected to adapt to the bearing requirements of the jacket foundation;

[0037] Quantitative analysis of sea state windows: Collect sea state statistics (including significant wave height, period, current velocity, and wave direction) for more than one year in the installation area. Use frequency domain hydrodynamic calculation methods to establish a dual-ship coupled hydrodynamic model using AQWA software to calculate six-degree-of-freedom added mass, radiation damping, and RAO; screen windows that meet the following conditions:

[0038] Environmental parameters: wind speed ≤13.8m / s, wave height ≤1.5m (operation stage) / ≤1.0m (preparation stage), current velocity ≤1.0m / s;

[0039] Motion thresholds: Floating body pitch / roll ≤ 3°, heave ≤ 200mm, pitch / roll ≤ 50mm;

[0040] Resonance avoidance: Avoid the resonance period of the gap between the two ships (kL=nπ).

[0041] S2: A semi-submersible barge carries the pre-assembled buoys of the ultra-large converter station pile foundation jacket to the construction sea area, and the barge is fixed in position by dropping a fixed anchor.

[0042] Prefabrication and loading of the jacket: The jacket is prefabricated in sections on land (upper cross brace section, main pipe section, lower cross brace section). During prefabrication, the pontoon (steel sealed structure with independent sealed chamber, no leakage in water pressure test) is assembled as an integrated unit. The jacket is pulled to the deck of a semi-submersible barge by a traction winch and fixed with M60 high-strength bolts and sea lashing.

[0043] Semi-submersible barge positioning: After the semi-submersible barge sails to the construction sea area, it will deploy 4 fixed anchors (arranged in a figure-eight shape, with the anchor chain length being 3 times the water depth) with the assistance of the anchor boat. The barge position will be adjusted through the anchor chain tension control system, with a positioning deviation of ≤0.5m.

[0044] S3: The floating crane enters the construction sea area and is aligned with the semi-submersible barge in a series or T-shaped arrangement to ensure the span conditions required for the lifting operation.

[0045] Floating crane vessel positioning: The floating crane vessel adopts DP dynamic positioning or anchor positioning, and is arranged in series or T-shape with the semi-submersible barge (with a spacing of 9.7m, the optimal spacing) to ensure a lifting span of 70-75m and a boom elevation angle of ≥60°.

[0046] Layout selection criteria: Tandem arrangement is suitable for waves with the same wave direction as the long axis of the hull (such as normal waves in the E direction), reducing pitching interference; T-shaped arrangement is suitable for transverse waves (such as strong waves in the NE direction), optimizing roll stability.

[0047] S4: Install rigging and wave compensation devices between the floating crane vessel and the jacket, install collision protection components, and deploy multi-buoy monitoring equipment to collect real-time data on the relative position of the two vessels, the motion status of the floating bodies, and the stress data of the rigging.

[0048] Rigging and wave compensation devices: High-strength steel wire rope rigging (safety factor ≥1.2) is installed, and the rigging tension deviation is ≤5%; an active wave compensation system is installed (compensation accuracy ±5mm) to counteract the effects of heave;

[0049] Monitoring equipment deployment: Installation on floating cranes, semi-submersible barges, and jacket structures:

[0050] GNSS positioning instrument (accuracy ±5mm, update frequency 10Hz) to collect the relative positions of the two ships;

[0051] A six-degree-of-freedom attitude sensor (accuracy ±0.1°) monitors the buoy's pitch, roll, and heave.

[0052] Tension sensor (range 0-10000t) to collect real-time force data on slings;

[0053] Underwater laser rangefinder (accuracy ±2mm) is used to measure the depth and spacing of the jacket structure in the water.

[0054] Collision protection: Inflatable fenders (1.5m in diameter, buffer capacity ≥100kJ) are deployed on the outside of the jacket and on the side of the semi-submersible barge.

[0055] S5: Untie the sea lashings between the jacket and the semi-submersible barge, and check the buoy sealing performance and the baseline status of the coupling response of the multi-buoy system;

[0056] Untying of marine lashings: Use hydraulic cutting tools to cut the marine lashings and check for any remaining connections;

[0057] System verification: Check the buoy sealing (pressure fluctuation ≤1%), semi-submersible barge ballast system (diving rate 0.3-0.5m / min), monitor equipment status, and collect multi-buoy coupling response baselines (pitch ≤1.5°, roll ≤1.2°, heave ≤120mm).

[0058] S6: Calculate the added mass and radiation damping of the dual-ship system based on the frequency domain hydrodynamic model, derive the structural buoyancy of the jacket structure by combining the water depth of the jacket structure, and substitute it into the load linkage logic formula (real-time load of semi-submersible barge = total weight of jacket structure and buoy box - total buoyancy of jacket structure - real-time lifting weight of floating crane), and coordinate the submersion of the semi-submersible barge and the loading of the floating crane until the jacket structure is completely separated from the semi-submersible barge.

[0059] Hydrodynamic parameter calculation: Based on the AQWA model, the central control console divides the entire lifting process into several typical working conditions and performs quasi-static calculations. Corresponding to the lifting process, the corresponding stages are substituted into the corresponding working conditions, considering the added mass of the two vessels and radiation damping (e.g., the added mass of the tandem floating crane vessels is 1.2 × 10⁻⁶). 10kg) and jacket buoyancy (F_total = structural buoyancy F_sound + buoyancy of the pontoon F_box, where F_sound varies with the water depth h_in, and h_in is positively correlated with the semi-submersible barge's diving depth h_submersible).

[0060] Load linkage control: Based on "real-time load of semi-submersible barge G_submersible = G_total - F_total - real-time load of floating crane P_actual", the semi-submersible barge submerges (rate 0.3-0.5m / min) and the floating crane loads (rate 30-50t / min) are controlled in a coordinated manner; when the relative motion between the two vessels exceeds 50mm, the submersible / loading rate is adjusted to compensate.

[0061] Detachment determination: When Gsubmersible ≤ 5t and the distance between the jacket and the semi-submersible barge is ≥ 2m, it is determined that the detachment is complete.

[0062] S7: The floating crane vessel lifts the jacket to the installation position, fine-tunes the attitude of the jacket through the attitude adjustment component, and removes the equipment after the jacket is fixed; among them, the coupling response control of the multi-floating body system is based on the dual-ship coupling hydrodynamic model based on the surface element method to avoid the risk of motion amplification caused by the resonance phenomenon between the two ships;

[0063] Dynamic displacement: The floating crane vessel moves to the installation position at a rate of 0.15-0.2 m / s, and the DP system corrects the vessel's position in real time.

[0064] Fine-tuning of posture: Lower the guide frame to 1m above the installation position and fine-tune it using a level and elevation gauge (each adjustment ≤10mm) to ensure that the levelness deviation is ≤0.2% and the elevation deviation is ≤30mm.

[0065] Permanent fixation: Lower the jacket to the seabed foundation, grout the gaps (C50 superfluid concrete), and test the load-bearing capacity and weld quality after 24 hours of curing.

[0066] Example 2

[0067] This embodiment uses the installation method provided in Embodiment 1 for a 9100t heavy-duty jacket foundation as an example. Regarding the multi-buoy coupling response characteristics, hydrodynamic calculation logic, and installation process requirements of floating cranes, semi-submersible barges, and jacket foundations, this embodiment focuses on the entire offshore installation process of a super-large converter station pile foundation jacket foundation (hereinafter referred to as "jacket foundation"). It elaborates on system configuration, preliminary preparation, core procedures, and quality verification in detail, ensuring that each step is deeply matched with theoretical foundations, numerical models, and process parameters.

[0068] I. Preset System Configuration and Technical Basis

[0069] 1.1 Core Equipment Parameters of Multi-Floating Body System

[0070] This implementation method uses clearly defined engineering-grade equipment to ensure that the hydrodynamic characteristics and coupling response of the multi-floating body system conform to the research conclusions. Specific parameters are as follows:

[0071] Floating crane vessel: A 12,000t self-propelled slewing "Zhenhua 30" type floating crane vessel is selected, with main dimensions of 320m length, 58m beam, and 28m depth, an operating draft of 18m (13.5m self-propelled draft), and a displacement exceeding 180,000 tons. The core operating equipment is a bow single-arm double-hook crane, with a rated lifting capacity of 12,000t in fixed operation (25m outboard working radius) and a rated lifting capacity of 7,000t in slewing operation. The main hook lifting height covers from 150m underwater to 120m above water, meeting the full-stroke requirements of the jacket structure from detachment from the semi-submersible barge to precise installation. The vessel's center of gravity coordinates are (174.11, 0.66, 26.7)m, and the DP (dynamic positioning) system reaches DP2 level, maintaining a positioning accuracy within ±1m in complex sea conditions.

[0072] Semi-submersible barge: The 15,000t "Zhen Semi-Submersible 1" type semi-submersible barge is selected. The hull type is a three-island semi-submersible box barge with main dimensions of 140m length, 70m beam, and 8.5m depth. The design draft is 4.5m, the maximum diving depth is 16.5m, the lifting capacity ranges from 8100 to 17000t, and the deadweight tonnage is 21000t. It can stabilize jacket structures ranging from 9100 to 19703t. The hull is equipped with 44 ballast tanks, and a precise diving rate of 0.3 to 0.5m / min can be achieved through the ballast adjustment system, meeting the linkage control requirements of "diving depth - jacket entry depth". The ship's center of gravity coordinates are (77, 0, 7.34)m. Three stern buoys are installed, and the stern buoy is detachable to accommodate structural avoidance requirements during jacket loading and unloading.

[0073] Jacket Structure: A 2000MW converter station pile foundation jacket structure is selected, employing an integral truss structure design with a total weight of 9100t (or adapted to 19703t according to project requirements). In the lateral support system, the upper horizontal brace elevation is -15.00m, and the lower horizontal brace corresponds to a mud surface elevation of -47.00m. A clearance of approximately 55.5m is reserved in the middle for the entry, exit, and positioning of semi-submersible barges. Regarding component specifications, the main pipe uses φ2400mm steel pipe, while the upper and lower horizontal braces and diagonal braces use φ1200mm and φ1500mm steel pipes respectively. Local reinforcement structures are installed at the diagonal brace intersections to cope with stress concentration during hoisting. The jacket is prefabricated and the pontoon is assembled as an integrated unit. The pontoon adopts a steel sealed structure, and its external dimensions and buoyancy parameters are matched with the total weight of the jacket (e.g., 19703t jacket with a fixed buoyancy of 13700t), ensuring that the total buoyancy can be dynamically adjusted in coordination with the diving depth of the semi-submersible barge.

[0074] 1.2 Core Technology Basis

[0075] Hydrodynamic calculation model: Based on potential flow theory and frequency domain / time domain motion equations, a coupled hydrodynamic model of a floating crane and a semi-submersible barge is established using AQWA software. The calculation range covers wave periods of 3.2 to 30 seconds and wave angles of 0° to 180° (in 45° intervals). It can output the additional mass coefficient, radiation damping coefficient, and response amplitude operator (RAO) of the two ships in six degrees of freedom: sway, roll, heave, pitch, pitch, and yaw. This provides a theoretical basis for the coupled response control of multi-floating bodies.

[0076] Two-ship arrangement schemes: Two typical schemes are selected: tandem arrangement and T-shaped arrangement. In the tandem arrangement, the two ships are aligned along the X-axis with their bows facing the positive X-axis direction and a distance of 9.7m. This is suitable for sea conditions where the wave direction is consistent with the long axis of the ship (such as normal waves in the E direction in the waters of Yangjiang City). In the T-shaped arrangement, the position of the floating crane remains unchanged, and the bow of the semi-submersible barge faces the positive Y-axis direction, with a distance of 9.7m. This is suitable for sea conditions with transverse or oblique waves (such as strong waves in the NE direction), and the amplitude of the roll motion can be reduced by optimizing hydrodynamic interference.

[0077] Load linkage logic: Establish a linkage logic of "real-time load of semi-submersible barge (G_submersible) = total weight of jacket + buoy (G_total) - total buoyancy of jacket (F_total) - real-time lifting weight of floating crane (P_actual)", where F_total = buoyancy of jacket structure (F_structure, which varies with water depth h_in) + fixed buoyancy of buoy (F_box). h_in is positively correlated with the submersible barge diving depth (h_submersible) (e.g., when h_submersible = 16.5m, h_in = 8m), ensuring that the load transfer process conforms to the hydrodynamic characteristics of multi-buoy.

[0078] II. Preliminary Preparation Stage

[0079] 2.1 Seabed exploration and preprocessing in the installation area (i.e., step S1)

[0080] Detection Range and Equipment: In accordance with the requirements of the operating sea area, a 200m × 200m detection area was demarcated based on the center point of the jacket installation. A multibeam sonar (0.1m resolution) and a side-scan sonar were used for joint scanning to simultaneously record the seabed topography, geological composition, and obstacle distribution. The multibeam sonar's line spacing was set to 10m to ensure full coverage without omissions; the side-scan sonar had a scanning width of 100m on each side, which could clearly identify protruding obstacles (such as rocks and shipwrecks) with a diameter ≥0.3m.

[0081] Data processing and preprocessing: The survey data is imported into a Geographic Information System (GIS) to generate a 3D seabed topographic map, marking anomalous areas (such as localized silt thickness exceeding 5m or rock protrusions exceeding 0.3m in height). For protruding obstacles, underwater blasting combined with mechanical debris removal is used: first, underwater drilling rigs are used to drill holes 1-1.5m deep in the rock, filled with emulsion explosives (≤5kg per hole), and remotely controlled blasting is used to break the rock to 0.5m below the seabed; then, a grab dredger is used to remove the broken debris, ensuring that the seabed flatness error after cleaning is ≤0.3m. For areas with excessively thick silt, silt solidification is used: cement slurry (water-cement ratio 1:1.5) is injected into the silt layer using an underwater jet pump, with a solidification depth ≥2m. After solidification, the foundation bearing capacity must be ≥150kPa to meet the bearing requirements of the jacket foundation.

[0082] Sea state window filtering: Based on sea state statistics for Yangjiang City (valid wave height H throughout the year) 1 / 3 The average value is 1.13m, the average period T is 5.71s, the normal wave direction is E, and the strong wave direction is NE. Based on the calculation results of the AQWA hydrodynamic model, the operation window is selected as follows:

[0083] Environmental parameter thresholds: wind speed ≤13.8m / s (corresponding to Beaufort scale 6), significant wave height ≤1.5m (operation stage) / ≤1.0m (preparation stage), tidal current velocity ≤1.0m / s;

[0084] Multi-body motion thresholds: for floating cranes and semi-submersible barges, the pitch / roll angle is ≤3°, the heave amplitude is ≤200mm, and the pitch / roll displacement is ≤50mm;

[0085] Resonance avoidance: Avoid the resonance period of the gap between the two ships (wave number kL=nπ, n is an integer) through RAO analysis. For example, the resonance period is 6.1~6.4s when arranged in series and 8~8.5s when arranged in a T-shape, so as to ensure that the wave period is far away from the resonance range during the operation period.

[0086] 2.2 Onshore prefabrication of jacket structure and assembly of pontoon (preliminary process of step S2)

[0087] Segmented prefabrication process: The jacket structure is prefabricated in three segments: upper cross brace segment, main pipe segment, and lower cross brace segment.

[0088] Main pipe section: Q345C grade steel plate is selected and rolled into φ2400mm steel pipe by plate rolling machine. The length of a single section is 15~20m. It is welded by submerged arc automatic welding. After welding, 100% ultrasonic flaw detection (UT) and 20% radiographic flaw detection (RT) are carried out to ensure that the weld quality level reaches Grade I in GB / T 19418-2010.

[0089] Horizontal and diagonal bracing sections: φ1200mm and φ1500mm steel pipes are used respectively. The ends are cut according to the design angle, fixed with special tooling, and welded to the main pipe. During the welding process, a total station is used to monitor the verticality of the components, and the deviation is controlled to ≤0.1%.

[0090] Node reinforcement: Weld a 20-30mm thick reinforcing plate at the intersection of the diagonal braces. The welding of the reinforcing plate to the main pipe and diagonal braces shall be done with fillet welds and the weld leg height shall be ≥15mm to avoid stress concentration at the nodes during hoisting.

[0091] Integrated assembly of floating boxes: such as Figure 2 As shown, the pontoon adopts a rectangular sealed structure, made of Q235B grade steel plate with a wall thickness of 8~10mm. Internally, it is equipped with transverse and longitudinal partitions (spaced 3~5m apart), forming multiple independent sealed chambers (to prevent a sudden drop in buoyancy due to single-point leakage). During assembly, the pontoon's installation position on the jacket is first located using a total station (symmetrically distributed on both sides of the main pipe). Then, CO2 gas shielded welding is used to weld and fix the pontoon to the main pipe of the jacket. After welding, a hydrostatic test is conducted (test pressure 0.2MPa, pressure held for 30 minutes with no leakage) to ensure the pontoon's sealing performance, with a final buoyancy deviation ≤1%.

[0092] 2.3 Semi-submersible barge transport and positioning (i.e., step S2)

[0093] Jacket loading: The semi-submersible barge docks at the prefabricated land-based wharf and is submerged to deck level with the wharf surface (draft 4.5m) using a ballast system. A traction winch (500kN traction force) is then used to slowly pull the jacket to the center of the semi-submersible barge deck. A laser rangefinder is used to adjust the relative position of the jacket and the semi-submersible barge, ensuring that the deviation between the jacket's center of gravity and the barge deck center is ≤0.5m. Subsequent installation of sea lashing: M60 high-strength bolts (material 42CrMo) are welded between the jacket's main pipe and the semi-submersible barge deck. Each main pipe is equipped with 8-12 sets of sea lashing, with the bolt preload reaching 100% of the design value to ensure no displacement of the jacket during transportation.

[0094] Navigation and Positioning: The semi-submersible barge navigates to the construction area using a combination of self-propelled propulsion and tugboat assistance. During navigation, sea conditions (wind speed, wave height, current speed) are monitored in real time. If sea conditions exceed safety thresholds (wind speed > 15 m / s, wave height > 2.0 m), the barge enters a nearby safe harbor to wait. Upon arrival at the construction area, four fixed anchors (arranged in a V-shape) are deployed with the assistance of two anchor boats. The anchor chain length is three times the water depth of the work area (e.g., 105 m for a water depth of 35 m), and the anchor weight is ≥ 5 t (to ensure grip). The tension of each anchor chain is adjusted using an anchor chain tension control system (accuracy ±1%) to ensure the semi-submersible barge's positioning deviation is ≤ 0.5 m, and the bow orientation is aligned with the prevailing wave direction (e.g., E-direction), creating conditions for subsequent docking with the floating crane.

[0095] 2.4 Floating crane vessel positioning and dual-vessel layout optimization (i.e., step S3)

[0096] Navigation and positioning of the floating crane vessel: The floating crane vessel "Zhenhua 30" set sail from a nearby port and navigated autonomously to the construction area using the DP2 dynamic positioning system. During the voyage, the route was corrected in real time through satellite positioning. After reaching the target area, the vessel first confirmed that there were no obstacles on the seabed by sonar detection, and then activated the DP system for positioning. The positioning accuracy was ≤1m.

[0097] Twin-ship layout selection and centering:

[0098] The layout scheme is selected based on the real-time wave direction: When the wave direction is E (normal wave direction), a series arrangement is adopted: the stern of the floating crane vessel faces the side of the semi-submersible barge, the length of the two vessels is aligned along the wave direction, and the position of the floating crane vessel is adjusted by GNSS dual-antenna positioning technology to keep the distance between the two vessels at 9.7m (optimal distance), and the lifting span (distance from the center of the crane to the center of gravity of the jacket) is controlled at 75m (optimal span).

[0099] When the wave direction is NE (strong wave direction), a T-shaped arrangement is adopted: the position of the floating crane remains unchanged, the bow of the semi-submersible barge is adjusted to the positive direction of the Y axis (perpendicular to the wave direction), and the distance between the side of the semi-submersible barge and the stern of the floating crane is maintained at 9.7m by adjusting the anchor chain tension, and the lifting span remains 75m.

[0100] Centering accuracy verification: A laser centering instrument (accuracy ±0.1mm) is used to measure the relative position of the rotation center of the floating crane and the center of gravity of the jacket. The longitudinal centering deviation is ≤100mm and the lateral centering deviation is ≤50mm to ensure that the rigging is evenly stressed during lifting (prerequisite for load transfer).

[0101] 2.5 Rigging Installation and Monitoring System Deployment (i.e., Step S4)

[0102] Rigging Selection and Installation: Based on the total weight of the jacket structure and the number of lifting points (4-6 points, symmetrically distributed), select high-strength steel wire rope rigging (material 18×7+FC, diameter ≥120mm, breaking strength ≥1500kN, safety factor ≥1.2). Before installation, clean the jacket structure lifting lugs (remove rust and oil), and install wear-resistant bushings (nylon, 10mm thickness) inside the lugs to prevent rigging wear. Slowly lower the rigging to the lifting lug position using the main hook of the floating crane. Manually assist in threading the rigging into the lug and lock it with a pin (material 40Cr). Install anti-loosening nuts at both ends of the pin to ensure a secure connection between the rigging and the lug. After installation, adjust the tension of each rigging using a tension sensor (range 0-10000t, accuracy ±0.5%), controlling the deviation to ≤5% to prevent the jacket structure from tilting.

[0103] Wave compensation device and collision protection components: An active wave compensation system is installed between the main hook and rigging of the floating crane vessel. This system consists of hydraulic cylinders, displacement sensors, and a controller, which can detect the heave displacement of the floating crane vessel in real time (response time ≤0.1s). The heave effect is compensated by the extension and retraction of the hydraulic cylinders, with a compensation accuracy of ±5mm (stability requirement). Inflatable fenders (diameter 1.5m, length 5m, buffer capacity ≥100kJ) are installed on the outside of the jacket (1~2m from the side of the semi-submersible barge) and on the side of the semi-submersible barge. The fenders are fixed to the hull and jacket by chains to avoid collision damage caused by the coupled motion of multiple floating bodies (safety hazard).

[0104] Monitoring system deployment: Based on monitoring requirements, deploy multi-dimensional monitoring equipment as follows:

[0105] GNSS positioning device: GNSS receivers (accuracy ±5mm, data update frequency 10Hz) are installed at the bow and stern of the floating crane vessel and the bow and stern of the semi-submersible barge to collect the relative coordinates of the two vessels in real time and calculate the pitch and sway displacements.

[0106] Six-DOF attitude sensors: One attitude sensor (measurement range ±30°, accuracy ±0.1°, sampling rate 10Hz) is installed at the center of the floating crane deck, the center of the semi-submersible barge deck, and the top of the jacket structure to monitor pitch, roll, and heave angles and amplitudes.

[0107] Tension sensor: One tension sensor is connected in series on each rigging to collect the real-time load (P_real) of the floating crane.

[0108] Underwater laser rangefinder: Two underwater laser rangefinders (measurement range 0~50m, accuracy ±2mm) are installed on the side of the semi-submersible barge to measure the depth of the jacket in the water (h_in) and the distance between the jacket and the semi-submersible barge in real time.

[0109] Central Control Console: Connect all monitoring equipment data to the central control console of the floating crane vessel, realize real-time data visualization through dedicated software (update frequency 1Hz), and set abnormal alarm thresholds (such as triggering audible and visual alarms when the actual load exceeds the rated lifting weight by 85% or the relative movement exceeds 50mm).

[0110] 2.6 Untying of marine tethers and system check (i.e., step S5)

[0111] Untying of sea lashings: Use hydraulic cutting tools (cutting capacity ≥100mm steel plate) to cut the sea lashing bolts between the jacket and the semi-submersible barge. The cutting sequence is "both sides first, then the middle; top first, then bottom" to avoid unilateral stress that could cause the jacket to shift. After each set of sea lashings is cut, use a hoist (rated lifting capacity 50kN) to lift the bolts off the deck to prevent them from falling into the sea. After untying, use underwater camera equipment to check for any remaining connecting structures (such as weld beads or uncut bolts) between the jacket and the semi-submersible barge to ensure the jacket is unrestrained.

[0112] System status check:

[0113] Float box inspection: The internal air pressure of the float box is measured by the pressure sensor on the top of the float box (range 0~0.5MPa, accuracy ±0.01MPa). The pressure fluctuation is ≤1% compared with the initial air pressure (0.1MPa), confirming that there is no leakage in the float box.

[0114] Ballast system check: Start the semi-submersible barge ballast pump set (flow rate ≥ 1000 m³ / h), test the water injection and drainage functions of the 44 ballast tanks, and confirm that the ballast tank level control is normal through the level sensor (accuracy ± 10 mm), and the diving rate can be stabilized at 0.3~0.5 m / min;

[0115] Monitoring equipment calibration: Perform on-site calibration of GNSS positioning devices, attitude sensors, and tension sensors. For example, verify the GNSS positioning accuracy using a known distance (e.g., 100m), and calibrate the tension sensor using a standard weight (e.g., 100t) to ensure that the equipment measurement error is ≤1%.

[0116] Coupled response baseline acquisition: Under the current sea state, collect 10 minutes of multi-floating body motion data and record the baseline values ​​of pitch (≤1.5°), roll (≤1.2°), and heave (≤120mm) of the floating crane and semi-submersible barge, which will serve as a reference for subsequent dynamic control.

[0117] III. Core Operation Phase (i.e., steps S6~S7)

[0118] 3.1 Multi-floating body coupled response control and load transfer (step S6)

[0119] This stage is the core of the installation process, strictly following the "submersion-loading-detachment" logic. Through calculation of typical hydrodynamic parameters and load linkage control, the jacket structure is safely detached from the semi-submersible barge.

[0120] 3.1.1 Calculation of typical hydrodynamic parameters under typical working conditions

[0121] Calculation initiation conditions: Before the semi-submersible barge submerges, the central control console calls the AQWA dual-ship coupled hydrodynamic model, inputs real-time sea state parameters (wind speed, wave height, period, wave direction), and initiates hydrodynamic parameter calculation. The calculation frequency is synchronized with the monitoring data update frequency (1Hz). Because wave calculations are based on the ship's waterline (draft), and the ship's draft cannot be changed in real time, the entire lifting process is divided into several typical working conditions, and the lifting depth corresponding to the typical working conditions is substituted into the calculation.

[0122] Core parameter calculation:

[0123] Added mass and radiation damping: Based on the current wave period (e.g., 5~8s), calculate the added mass coefficient and radiation damping coefficient for the six degrees of freedom of the two ships. For example, the added mass of the floating crane ship in a series arrangement during pitching is 1.2 × 10⁻⁶. 10 kg (period 6.1s), semi-submersible ship roll radiation damping 2.5×10 9 Ns / m (period 8s) to determine whether there is a risk of resonance (such as a sudden increase in added mass or radiation damping peak exceeding the threshold).

[0124] Calculation of jacket buoyancy: The diving depth (hdive) of the semi-submersible barge is obtained using an underwater laser rangefinder. Based on the correlation between "hdive - hent" (e.g., when hdive = 16.5m, hent = 8m), the entry depth of the jacket (hent) is derived. Then, the structural buoyancy (Fstructure) is queried using the jacket buoyancy characteristic curve (pre-drawn based on model tests, with hent and Fstructure corresponding one-to-one). For example, when hent = 8m, Fstructure = 1995t. Finally, the total buoyancy Ftotal is calculated as Fstructure + Fbox (e.g., 1995t + 13700t = 15695t).

[0125] Required lifting weight calculation: Based on the load linkage logic, calculate the required lifting weight P_required = G_total - F_total (e.g., 19703t - 15695t = 4007t), which is used as the target value for the floating crane's load.

[0126] 3.1.2 Submersible Barge Descent Control

[0127] Submersion Initiation and Rate Adjustment: The semi-submersible barge ballast system is activated according to the principle of "bow first, then stern, symmetrical water injection," with an initial submersion rate set at 0.4 m / min. The central control console receives real-time feedback from the attitude sensors regarding the semi-submersible barge's roll angle. When the roll angle > 2°, the water injection volume in the roll-side ballast tank is reduced; when the roll angle > 3°, submersion is paused, and water is injected into the opposite ballast tank (500~1000 m³) until the roll angle drops to ≤ 1.5°, ensuring a smooth submersion process (stability requirement).

[0128] Diving Depth Monitoring and Correction: The diving depth (h_diving) is monitored in real time using the semi-submersible barge's draft gauge (accuracy ±5mm). The depth is compared with the target diving depth (e.g., 16.5m). If the deviation exceeds 0.1m, the ballast rate is adjusted. Upon reaching the target depth, the ballast pump unit is stopped, and the ballast tank level is kept stable. The semi-submersible barge's position is confirmed to be stable (deviation ≤0.3m) using a GNSS positioning system.

[0129] 3.1.3 Floating crane load control

[0130] Loading Initiation and Rate Control: The floating crane vessel initiates loading according to the principle of "slow and gradual increase, step-by-step loading," with an initial loading rate set at 40 t / min. The central control console receives the actual load (Pactual) from the tension sensor in real time and compares it with the required load (Pdemand). When the actual load reaches 80% of the required load (e.g., 3206 t), the loading rate is reduced to 20 t / min; when the actual load reaches 95% of the required load (e.g., 3807 t), the loading rate is reduced to 10 t / min to prevent a sudden increase in actual load from overloading the rigging. Figure 1 and Figure 3 As shown.

[0131] Wave compensation coordination: During the loading process, the active wave compensation system works in real time, adjusting the extension and retraction of the hydraulic cylinder according to the heave displacement of the floating crane (e.g., ±100mm) to compensate for the impact of heave on P_actual and ensure that the fluctuation amplitude of P_actual is ≤5% (load stability requirement).

[0132] 3.1.4 Coupling Response Compensation and Decoupling Determination

[0133] Coupled Response Monitoring and Compensation: The central control console calculates the relative motion amplitude (vector sum of sway, roll, and heave) of the floating crane and semi-submersible barge under multiple typical operating conditions. When the amplitude is >50mm, the compensation mechanism is activated: if it is mainly due to the roll of the semi-submersible barge, the water volume in the ballast tank of the semi-submersible barge is adjusted (e.g., water is injected into the right ballast tank); if it is mainly due to the heave of the floating crane, the compensation amount of the wave compensation system is increased; if it is mainly due to the sway of both ships, the thrust of the floating crane's DP system is finely adjusted (e.g., the thrust of the bow thruster is increased) until the relative motion amplitude drops back to ≤50mm.

[0134] Detachment Criteria: The jacket is considered to have completely detached from the semi-submersible barge when the following three conditions are met:

[0135] The real-time lifting capacity of the floating crane vessel, Pactual, equals Prequired (deviation ≤ 1%).

[0136] The real-time load of the semi-submersible barge is Gsubmersible = Gtotal - Ftotal - Pactual ≤ 5t (the conclusion that "Gsubmersible approaches 0 when disengaged").

[0137] The underwater laser rangefinder measures the distance between the jacket structure and the deck of the semi-submersible barge to be ≥2m (safe distance to avoid collision).

[0138] Confirmation after detachment: Stop the semi-submersible barge from submerging and the floating crane from loading. Use underwater camera equipment to observe that there is no contact between the jacket and the semi-submersible barge. Record the multi-buoy motion data at this time (such as pitch 1.3°, roll 1.1°, heave 110mm) as the reference for subsequent displacement.

[0139] 3.2 Jacket Pile Lifting and Precise Installation (Step S7)

[0140] 3.2.1 Dynamic displacement of floating crane vessel

[0141] Displacement path planning: Based on the installation location coordinates (pre-determined by multibeam detection) and the current position of the floating crane, a displacement path is generated at the central control console. The path avoids areas with seabed obstacles. The displacement distance is usually 100~500m, and the displacement rate is set to 0.15~0.2m / s (for stability requirements).

[0142] DP System Coordinated Relocation: The floating crane vessel activates the DP2 dynamic positioning system and moves slowly along the planned path. During the movement, the GNSS positioning instrument provides real-time feedback on the vessel's position deviation (≤0.5m). The DP system automatically adjusts the thrusters (bow, stern, and side thrusters work together) to correct the position deviation. Simultaneously, attitude sensors monitor the floating crane vessel's pitch and roll angles in real time. When the angle is >2°, the relocation rate is reduced (e.g., to 0.1m / s) to ensure that the jacket structure does not sway significantly during the relocation process.

[0143] 3.2.2 Fine-tuning of the catheter holder posture

[0144] Attitude monitoring and preliminary adjustment: Hoist the jacket to a position 1m above the installation location, pause the movement, and measure the levelness using a level (accuracy ±0.01°) mounted on top of the jacket, and measure the pile top elevation using a GNSS-based elevation measuring instrument (accuracy ±5mm). If the levelness deviation is >0.2% or the elevation deviation is >30mm, make preliminary adjustments using the boom and slewing functions of the floating crane: correct the levelness deviation by adjusting the crane's slewing angle (single adjustment ≤1°), and correct the elevation deviation by adjusting the hook lifting height (single adjustment ≤10mm).

[0145] Fine-tuning and locking: When the levelness deviation is ≤0.2% and the elevation deviation is ≤30mm, fine-tuning is initiated: By controlling the tension of each rigging (with tension sensor feedback, single adjustment amount ≤5t), the levelness is further optimized to ensure the deviation is ≤0.15%; the floating crane position is fine-tuned through the DP system (single adjustment ≤0.3m) to align the jacket foundation legs with the pre-drilled holes in the seabed foundation (alignment deviation ≤20mm). After fine-tuning, the floating crane and DP system are locked to ensure the stability of the jacket foundation attitude.

[0146] 3.2.3 Lowering and Permanent Fixation of the Tractor Stent

[0147] Slow descent control: Activate the descent function of the floating crane, setting the descent rate to 0.1~0.15 m / min. During descent, monitor the levelness and elevation of the jacket in real time. If the deviation exceeds the threshold (levelness > 0.2%, elevation > 30 mm), immediately pause descent and readjust the attitude. When the jacket legs contact the seabed foundation, stop descent and measure the bearing capacity of the legs using pressure sensors (installed at the bottom of the legs, range 0~5000 kN), ensuring that the bearing capacity deviation of each leg is ≤10%.

[0148] Grouting and Fixing: Underwater grouting equipment (grouting pressure 0.5~1.0MPa, flow rate 50~100L / min) is used to grout the gap between the jacket foundation legs and the seabed foundation. The grouting material is superfluid concrete (strength grade C50, initial setting time ≥4h), and the grouting height is from the top surface of the seabed foundation to 1~2m inside the jacket leg. During the grouting process, the grout density is monitored using an ultrasonic detector (accuracy ±1mm) to ensure there are no voids. After grouting, curing is carried out for 24 hours, during which the jacket foundation posture is monitored in real time to prevent posture deviation during curing. Figure 4 , 5 As shown in Figure 6, Figure 4 This is a schematic diagram of the pile positions during the installation of the jacket structure; Figure 5 Flowchart for the installation of jacket foundation piles; Figure 6 This is a schematic diagram showing the installation locations of the jacket, the floating crane, and the semi-submersible barge.

[0149] 3.2.4 Installation quality inspection and equipment removal

[0150] Quality Inspection: After maintenance is completed, an installation quality inspection will be conducted.

[0151] Attitude detection: The levelness of the jacket structure and the elevation of the pile top were re-measured using a level and an elevation measuring instrument (deviation ≤ 0.2%), which met the accuracy requirements of the converter station pile foundation;

[0152] Bearing capacity testing: The bearing capacity of the jacket foundation was tested by surcharge test (surcharge amount is 1.2 times the design bearing capacity), stabilization time is 1 hour, and settlement is ≤10mm;

[0153] Weld inspection: The welds connecting the jacket structure and the subsea foundation are subjected to 100% UT (under-the-earth) and 20% RT (reverse irradiation) inspections, and the weld quality reaches Grade I.

[0154] Equipment withdrawal: After passing the inspection, the rigging, wave compensation system, collision protection components and monitoring equipment are removed: First, the rigging pins are removed, and the rigging is slowly retrieved by the floating crane; then the monitoring equipment is removed, and the equipment is cleaned and calibrated for future reuse; finally, the floating crane and semi-submersible barge withdraw from the construction area in sequence. Before the semi-submersible barge withdraws, it uses the ballast system to deplete water and float to the design draft (4.5m), and the floating crane autonomously navigates to the next work site or port using the DP system.

[0155] IV. Verification of Key Control Effects

[0156] 4.1 Verification of Cooperative Stability of Multi-Floating Bodies

[0157] Motion response indicators: Using data from attitude sensors and GNSS positioning devices, it was verified that the pitch / roll angle of the floating crane and the semi-submersible barge is ≤2.5° (≤preset threshold 3°), the heave amplitude is ≤180mm (≤preset threshold 200mm), and the relative motion amplitude is ≤45mm (≤preset threshold 50mm), which meets the requirements of dual-ship coupled response control and there is no abnormal motion caused by hydrodynamic interference.

[0158] Resonance avoidance effect: Through calculation by AQWA model and comparison with real-time monitoring data, the wave period during the operation period is far away from the resonance period of the two ships (such as avoiding 6.1~6.4s when arranged in series), and there is no sudden increase in added mass and radiation damping, which verifies the effectiveness of resonance avoidance measures.

[0159] 4.2 Security Verification of Load Transfer

[0160] Load distribution accuracy: Through tension sensor and semi-submersible barge ballast system data, it is verified that the deviation between the real-time lifting weight Pactual of the floating crane and the required lifting weight Prequired is ≤1% (e.g., Pactual = 4007t, Prequired = 4007t), the real-time load Gsubmersible of the semi-submersible barge is ≤5t (e.g., Gsubmersible = 0t), the load transfer error is ≤5%, which conforms to the load linkage logic and there is no overload or sudden drop phenomenon.

[0161] Rigging stress stability: Through tension sensor data, it is verified that the tension fluctuation of the rigging is ≤5% (e.g., average tension 4007t, fluctuation range 3807~4207t), there is no sudden increase in tension caused by coupling motion, and the safety factor of the rigging is always ≥1.2.

[0162] 4.3 Verification of Installation Accuracy

[0163] Posture accuracy: The final test showed that the horizontal deviation of the jacket was 0.18% (≤0.2%) and the elevation deviation of the pile top was 28mm (≤30mm), which met the installation accuracy requirements of the pile foundation and could support heavy equipment such as converter valves and transformers (core functional requirements).

[0164] Structural safety: The load-bearing capacity test and weld inspection results show that the bearing capacity of the jacket foundation reaches 1.2 times the design value, the connection welds are defect-free, and the structural safety meets the GB 50205-2020 "Standard for Acceptance of Construction Quality of Steel Structures" and can meet the operational needs of the entire life cycle (≥25 years).

[0165] This embodiment refines the equipment selection, operation process, and control standards for each step, fully implementing the multi-floating body coupling response theory, hydrodynamic calculation model, and load linkage logic into the installation process. This ensures the safety, stability, and accuracy of the offshore installation of the pile foundation jacket of the ultra-large converter station, providing a reusable technical solution for similar projects.

[0166] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for offshore installation of a pile foundation jacket for an ultra-large converter station, characterized in that, Includes the following steps, S1: Conduct a seabed survey of the jacket installation area, combine it with the sea state statistics of the installation area, obtain the response amplitude operator of the multi-buoy system through frequency domain hydrodynamic calculation method, and select a suitable operating window; S2: A semi-submersible barge carries the pre-assembled buoys of the ultra-large converter station pile foundation jacket to the construction sea area, and the barge is fixed in position by dropping a fixed anchor. S3: The floating crane enters the construction area and aligns itself with the semi-submersible barge to ensure the required span for the lifting operation. S4: Install rigging and wave compensation devices between the floating crane vessel and the jacket, install collision protection components, and deploy multi-buoy monitoring equipment to collect real-time data on the relative position of the two vessels, the motion status of the floating bodies, and the stress data of the rigging. S5: Untie the sea lashings between the jacket and the semi-submersible barge, and check the buoy sealing performance and the baseline status of the coupling response of the multi-buoy system; S6: Calculate the added mass and radiation damping of the dual-ship system based on the frequency domain hydrodynamic model, derive the structural buoyancy of the jacket structure by combining the water depth of the jacket, substitute it into the load linkage logic formula, and coordinate the submersible barge's submersion and the floating crane's load loading until the jacket structure is completely separated from the semi-submersible barge. S7: The floating crane vessel lifts the jacket to the installation position, fine-tunes the attitude of the jacket through the attitude adjustment component, and removes the equipment after the jacket is fixed; among them, the multi-floating body system coupling response control is based on the dual-ship coupled hydrodynamic model based on the surface element method to avoid the risk of motion amplification caused by the resonance phenomenon between the two ships.

2. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 1, characterized in that, The logical formula in step S6 is: Real-time load of semi-submersible barge = Total weight of jacket and buoy - Total buoyancy of jacket - Real-time lifting weight of floating crane.

3. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 2, characterized in that, In step S1, a multibeam detector is used to scan the seabed in the area where the jacket is installed.

4. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 3, characterized in that, The operation window selection in step S1 needs to take into account the wind, wave, and current characteristics of the installation sea area and the motion threshold of the multi-buoy system. By analyzing the response amplitude operator, it is necessary to avoid sea conditions that are prone to resonance and ensure that the motion state of the floating body meets the installation operation requirements.

5. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 4, characterized in that, In step S3, the floating crane and the semi-submersible barge are arranged in series or in a T-shape to achieve centering and positioning.

6. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 5, characterized in that, The arrangement of the two ships needs to be selected based on hydrodynamic interference analysis: tandem arrangement is used for sea conditions where the wave direction is consistent with the long axis of the hull; T-shaped arrangement is used for sea conditions with transverse or oblique waves.

7. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 6, characterized in that, The multi-buoy monitoring equipment in step S4 includes a GNSS positioner, a six-degree-of-freedom attitude sensor, and a sling tension sensor. The equipment data update frequency must meet the real-time control requirements to ensure timely feedback on the relative motion status of the two ships. When the relative motion amplitude exceeds the preset range, an adjustment mechanism is triggered.

8. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 7, characterized in that, The buoyancy of the jacket structure in step S6 needs to be obtained by combining the jacket's water entry depth and its own buoyancy characteristics. The total buoyancy is the sum of the structural buoyancy and the buoyancy of the pontoon. The load linkage logic needs to synchronously associate the effects of the added mass of the two ships and the radiation damping on the load transfer.

9. The method for offshore installation of the jacket foundation of an ultra-large converter station according to claim 8, characterized in that, In step S6, the diving rate of the semi-submersible barge and the loading rate of the floating crane need to be dynamically adjusted based on the relative motion of the two vessels. The diving rate should be controlled at 0.3-0.5 m / min, and the loading rate should be controlled at 30-50 t / min to ensure the stability of the multi-buoy system.

10. The method for offshore installation of the pile foundation jacket of an ultra-large converter station according to claim 9, characterized in that, The attitude adjustment components in step S7 include a level and an elevation gauge.

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