GB/T 47721-2026Wind energy generation systems - Design specification for integrated support structures of offshore wind turbines (English PDF)

6.1 General Rules

6.1.1 External conditions should include wind conditions, ocean conditions, geological conditions, and earthquakes, etc.

6.1.2 Integrated design should take into account the impact of environmental and power grid conditions on the construction and operation of offshore wind farms.

6.1.3 Integrated design should take into account normal external conditions during operation as well as extreme external conditions with different return periods.

6.1.4 The area for offshore wind farm projects should ideally include at least one year of measured wind data. The measurement method should comply with the provisions of GB/T 18709. The data should include measured time-series data such as wind speed, wind direction, temperature, and air pressure. The review, interpolation, and correction of wind measurement data should be carried out in accordance with... The provisions of GB/T 37523.

6.1.5 The completeness of valid wind measurement data for offshore wind farms shall not be less than 90%, and the calculation method shall comply with the provisions of GB/T 18710.

6.1.6 The offshore wind farm project area should include at least one year of measured hourly water level, wave, and ocean current data, as well as measured seabed topography and historical data. Historical charts. Related data should comply with GB/T 51308 and should be prepared in accordance with GB/T 31517.1-2022 for marine hydrological and environmental data collection. Environmental condition assessment.

6.1.7 In the absence of long-term measured data for the engineering area, numerical simulations of the marine hydrological conditions in the engineering area should be conducted, based on the simulations. The results were statistically analyzed to determine the marine conditions such as waves, currents, water levels, and sea ice at any location in the project area.

6.1.8 The environmental condition parameters and their joint probability distribution should include the following.

a) Wind conditions. Wind speed, wind direction distribution, and turbulence intensity are obtained through long-term measured data or high-precision wind resource assessment models;

b) Waves. Wave height, wave period, and wave direction are obtained through wave observation data or high-precision wave numerical models;

c) Ocean currents. Obtain current velocity and direction through ocean current observation data or high-precision ocean current numerical models;

d) Water level. Water level changes are obtained through methods such as water level observation or high-precision numerical simulation;

e) Sea ice. Obtain ice thickness, ice velocity, ice orientation, and sea ice data through field observations, field sampling experiments, satellite remote sensing, or high-precision numerical models. Strength, etc.;

f) Geology. Obtain soil layer distribution, physical and mechanical parameters through geophysical, geotechnical engineering investigation and indoor geotechnical tests.

6.2 Wind conditions

6.2.1 The wind condition model used for integrated load analysis shall meet the requirements of GB/T 18451.1-2022.

6.2.2 The wind speed probability distribution model should be determined based on the wind measurement results of the engineering site, and the calculation method in GB/T 18451.1-2022 can be adopted.

6.2.3 The turbulence values at different wind speeds for offshore wind farm sites should be determined based on measured wind resource data, and the wake of the offshore wind farm should be taken into account. Influence.

6.2.4 The 10-minute average wind speed Vhub, which occurs once every 50 years, should be evaluated using extended data from nearby reference meteorological stations or numerical models. Estimate. In tropical and subtropical regions, when tropical and temperate cyclones dominate, Monte Carlo simulation methods can be used to assess the extreme winds of tropical cyclones. For specific methods, please refer to Appendix J of GB/T 18451.1-2022.

6.2.5 The calculation of air density at offshore wind farm sites shall be in accordance with the provisions of GB/T 18710.

6.2.6 If the project site is located in a typhoon-prone area, the integrated load analysis should consider the impact of typhoons, and the typhoon wind conditions should comply with GB/T 31519. According to the regulations.

6.3 Waves

6.3.1 The wave characteristic parameter values used in the integrated design meet the requirements.

a) The NSS condition should obtain the long-term joint probability distribution of Vhub, Hs, and Tp for hub height, as well as the joint probability of wind direction and wave direction. distributed.

b) The SSS condition should consider a combined probability of Hs and wind speed of once in 50 years under normal power generation conditions, which can be based on the marine meteorological conditions of the site. The data were determined by extrapolation using the "reverse first-order reliability analysis method," the specific method of which can be found in the appendix of GB/T 31517.1-2022. The provisions of F shall apply; or a return period of Hs,50 shall be used as a conservative value.

c) ESS conditions should consider return periods of Hs,50, Hs,1 and the corresponding Tp range; return periods of H50, H1 and the corresponding wave periods. scope.

6.3.2 Irregular wave trains in random sea states should be analyzed using wave spectra. The wave spectra should be tailored to the geographical region and the severity of the sea state being simulated. Degree and related usage conditions are determined.

a) When the wave pattern in an offshore wind farm is dominated by wind waves, PM

2.5 should be used for wave and fatigue analysis of fully developed, unlimited wind areas. Wave pattern or Wensheng's standard pattern;

b) When analyzing waves and extreme conditions in different growth stages and limited wind zones, it is advisable to use the Jonswap wave spectrum or the Wensheng constant spectrum;

c) Depending on the actual conditions of the sea area where the project is being carried out, other wave spectrum forms may also be used.

6.3.3 Fatigue load calculations should consider the NSS corresponding to different average wind speeds, and the number of sea states and average wind speeds should be determined through sensitivity analysis. The wind speed resolution is reasonable.

6.3.4 The long-term joint probability distributions of Vhub, Hs, and Tp, as well as the joint probability distributions of wind direction and wave direction, shall comply with GB/T 31517.1-2022. According to the regulations.

6.3.5 Wave characteristic values under ESS should be evaluated based on long-term marine meteorological databases. If sufficient marine meteorological data is unavailable... According to the range of maximum wave height and associated wave period that can be used to assess, it is advisable to refer to GB/T 31517.1-2022 for assessment.

6.4 Ocean currents

6.4.1 The assessment of ocean current characteristics should provide the tidal current type, spatiotemporal variation patterns of ocean currents, ocean current vector map, and the maximum possible tidal current velocity for the engineering sea area. Contents such as flow characteristics.

6.4.2 The design current condition assessment should consider the following components in conjunction with the current characteristics of the target area.

a) Utide caused by tides, storm surges, and changes in atmospheric pressure;

b) Uwind. The total flow velocity should be the vector sum of the above components, and the velocity of water particles caused by waves should be the vector superposition of the ocean current velocity. Ocean currents affect... The effects of wavelength and wave period are generally small and can be ignored. For specific distribution models of ocean current components, please refer to GB/T 31517.1-2022.

6.5 Water level

6.5.1 The water level condition assessment should provide the elevation datum transformation relationship of the engineering site, as well as HAT, LAT, MSL, storm surge increase/decrease, etc. The characteristic values are shown in Figure

3.For areas significantly affected by tides, the mean high tide level, mean low tide level, maximum tidal range, and minimum tidal range should also be given. Characteristic values such as tidal range, mean tidal range, mean duration of rising tide, and mean duration of ebb tide.

6.5.2 For wind farm projects in sea areas sensitive to sea level rise, the impact of sea level rise on water level should be considered.

6.6 Sea Ice

6.6.1 The sea ice survey area should include the engineering site and surrounding sea area, and collect data on ice period, ice thickness, ice concentration, ice intensity, and ice cover. Information such as ice type, sea ice drift direction, ice speed, and ice disc measuring tool.

6.6.2 The design sea ice condition assessment should include the following parameters.

a) Basic parameters of sea ice, including effective ice period; extreme values of ice thickness in 1-year and 50-year cycles, sea ice compressive strength, sea ice flexural strength, and flatness. Average ice speed, main direction of sea ice;

b) Joint probability distribution of ice thickness, ice velocity, and ice direction.

6.7 Marine life

6.7.1 The thickness of marine organisms and its dependence on water depth should be assessed based on validated references, local experience, and existing measurement results. Dependence. It is advisable to conduct studies on specific sites to determine the nature, thickness, and variation of marine organisms with water depth.

6.7.2 The influence of attached marine organisms on the cross-sectional area of structural components can be evaluated using the equivalent diameter method. The equivalent diameter can be calculated using formula (1). calculate.

6.7.3 The surface roughness (k) of the structural components with attached marine organisms is taken as 0.005m~0.05m. Its influence on wave and current loads can be assessed using equal... The method of evaluating the effective hydrodynamic coefficient is used.

6.7.4 The density of attached marine organisms should be determined through actual surveys. If no measured data is available, a value of 1300 kg/m^3 to 1400 kg/m^3 can be used.

6.8 Geological conditions

6.8.1 An engineering geological condition assessment should be conducted for offshore wind farm projects, including an overview of the hydrogeology, environmental water and soil corrosivity. Analysis, adverse geological processes, site soil type classification, site category classification, site stability and suitability evaluation, feasibility analysis of natural foundations, marine Feasibility analysis of foundation selection and pile driving for wind farms, etc. Soil and rock classification should comply with GB 50021, and seabed elevation should be based on local conditions. The results of topographic measurements and seabed evolution have been confirmed.

6.8.2 The engineering geological survey of offshore wind farm sites shall be conducted at and around the location of the offshore wind turbine generator sites. The survey area shall be... It covers all offshore wind turbine generator sites in offshore wind farms.

6.8.3 The engineering geological survey of offshore wind farm sites shall include at least the following. water depth and seabed topography, seabed surface conditions, and natural features. Or man-made seabed obstacles, structural characteristics, spatial distribution and physical and mechanical properties of seabed strata, geological hazards and seismic factors.

6.8.4 The geological parameters for foundation or anchor design should be based on the foundation type, engineering geological survey results, in-situ test results, and indoor geotechnical test results. The results of static load tests on pile foundations in the engineering site can be used to determine the overall situation.

6.8.5 The scour protection design of offshore wind turbine pile foundations should be based on seabed topography and geological conditions, ocean currents and wave characteristics, and foundation type, etc. Based on information, combined with the results of seabed evolution and local scour analysis, and after technical and economic comparisons, the scour protection design for shallow foundations should be determined in conjunction with numerical models. The results of the simulated water tank test will determine the outcome. During the construction and operation phases, the scouring of the foundation should be monitored.

6.9 Seismic conditions

6.9.1 The integrated design shall determine the following seismic conditions.

a) Historical seismic activity in the project area, as well as recent seismic activity and signs;

b) Seismic ground motion parameters such as peak ground acceleration, basic seismic intensity, and characteristic period of the engineering area;

c) Analysis of the possibility of liquefaction, slippage and subsidence of the seabed in the project area due to earthquakes.

6.9.2 Seismic design should preferably use site ground motion parameters that have undergone seismic safety evaluation and have been approved. Site ground motion parameters should include... Peak ground acceleration and acceleration response spectrum. If measured seismic acceleration records cannot be obtained during the design phase, then seismic safety should be considered. During the evaluation, the site-related seismic spectrum was evaluated and fitted.

6.9.3 The time-history load analysis method should be used for the calculation of seismic loads on offshore wind turbine generators and their supporting structures.

6.10 Power Grid Conditions Under normal operating conditions, the system can be set to handle 20 power outages per year, with each outage lasting no more than 6 hours. In extreme conditions, the system should be configured to handle power outages as follows: The setup process will last for 3 months. The definition and requirements for the site's power grid conditions should comply with GB/T 18451.1-2022 and GB/T 19963.2. The decision will be made.

6.11 Other environmental conditions Other environmental conditions should consider the impact of air temperature, water temperature, humidity, salinity, unit icing, and tidal surge on the integrated design. The parameters can be determined based on representative values or the range of variation in environmental conditions. When selecting design values, the possibility of multiple conditions occurring simultaneously should be considered.

7.1 General Rules

7.1.1 The integrated model of the support structure for a stationary offshore wind turbine should include the rotor-nacelle assembly, the tower model, and the substructure model. And the basic model. The integrated model of the support structure for a floating offshore wind turbine should include the rotor-nacelle assembly, the tower model, and the floating... A model of the basic structure and anchoring system. The wind turbine-nacelle assembly should include the wind turbine, transmission and power generation system, structural components, control system, and other key components. Components and systems.

7.1.2 Integrated modeling should take into account key external environmental factors that affect the operation of offshore wind turbines.

7.1.3 The basic model should consider the nonlinear stiffness and damping of the foundation and subgrade under different external loads. If analysis proves that it will not affect the sea... The dynamic and load responses of the supporting structure above the mud surface are affected, and it is permissible to use the mud surface stiffness, mass, and damping matrix instead of the mud surface below the mud surface. The interaction between the foundation and the soil.

7.1.4 The multibody dynamics model and the finite element analysis model used in the integrated support structure design should maintain consistency in dynamic characteristics. They should have the same mass distribution and moment of inertia, and for the same modeled object under the same boundary conditions, this should be confirmed through comparative calculations. The deviation of the first-order modal frequency of the model should not exceed 2%.

7.1.5 The wind turbine generator model shall meet the requirements of GB/T 18451.1-2022.

7.1.6 Integrated modeling of offshore wind turbine generators should use different local coordinate systems for different structural components, as shown in Figure 4.

7.6 Fixed Substructure

7.6.1 For fixed substructure models, beam elements should be used for modeling, including node coordinates, section properties, material properties, and aerodynamic and hydrodynamic drag. Coefficients and other parameters.

7.6.2 Flanges in the substructure should preferably be modeled as mass points. Auxiliary components and electrical equipment that do not affect the overall structural stiffness should also be considered. The components should be modeled using mass points.

7.6.3 The simulation of the substructure should take into account the influence of environmental conditions, including erosion, corrosion, and marine organism attachment. In particular, extreme operating conditions should be considered. Considering the extreme values of scour depth and corrosion amount, the average scour depth and average corrosion amount should be considered for fatigue conditions.

7.7 Floating Foundation Structure

7.7.1 Suitable finite element models should be used to model floating foundation structures. The mass and stiffness properties of these elements should be based on the actual floating structure. The floating foundation structure is equivalent to that of a real floating foundation structure to reasonably represent its characteristics. If the elasticity of the floating foundation structure is verified through analysis... If the influence of the property on the overall dynamic characteristics is negligible, it can be simplified to a rigid body model. The hydrodynamic load model of a floating foundation structure should be modeled using the following two methods, and its hydrodynamic parameters should be based on pool tests or high-altitude tests. The quality CFD numerical simulation results were compared and calibrated, and the relevant requirements were in accordance with GB /Z 44047-2024.

a) Potential flow theory superimposed with Morrison's formula for viscous drag force.

b) Potential flow theory superimposed with hydrodynamic viscous damping matrix.

7.7.2 The equivalent model of a floating support structure should ensure consistent structural stiffness in the main stress directions. This applies to floating foundation structures or partially floating structures. For basic structures, finite element or multibody models should be used to characterize the elastic deformation of the structure, and beam elements should be used to simulate the flexible characteristics of slender structures.

7.7.3 The integrated support structure design of floating offshore wind turbine generators should be verified by pool testing or CFD simulation to validate hydrodynamic performance. Sensitivity of factors such as drag force coefficient, flow load, hydrodynamic damping and slamming in the force model.

7.7.4 The floating foundation structure model should take into account the effects of environmental conditions such as corrosion and marine organism attachment.

7.8 Basics

7.8.1 The foundation should be simulated using a reasonable mechanical model to ensure that the model's stiffness and mass are consistent with the actual structure.

a) Pile foundations and other rod-like structures can be simulated using beam elements or shell elements;

b) Thin-walled structures such as cylindrical foundations can be simulated using shell elements or equivalent models;

c) Complex structures welded from steel plates should be simulated using shell elements or equivalent models, depending on the actual structure.

7.8.2 Basic modeling should fully consider the interaction characteristics between different foundation types and soil.

a) The jacket pile foundation was simulated using PY, TZ, and QZ curves;

b) Single pile and cylindrical foundations adopt three-dimensional finite element or other equivalent models.

8.1 General Rules

8.1.1 The time-history load analysis method should be used for integrated load analysis.

8.1.2 Integrated load analysis should include environmental loads such as wind, waves, ocean currents, and sea ice that the unit may experience throughout its entire life cycle, as well as the unit's drive systems. Loads, gravity and inertial loads, ship impact loads, seismic loads, and other loads are taken into account. The results should include permanent loads over the service life. Loads include environmental loads, deformation loads, variable loads, accidental loads, seismic loads, normal service loads, and transportation and installation loads. (Integrated) The load analysis empirical verification should be carried out in accordance with the provisions of GB/T 37257.

8.1.3 The integrated load analysis of the support structure of offshore wind turbine generators should take into account the natural period of the support structure, the natural period of the waves, and the overall dynamics. Mechanical properties are assessed to comprehensively evaluate the dynamic response of the entire system and supporting structure under wave action, with wave action fully covering key operating conditions. Based on this, a simplified process was performed.

8.1.4 Load output is divided into ultimate load and fatigue load, including statistical load and time history load of each node of the tower and foundation structure.

8.1.5 The post-processing of load results under different extreme working conditions shall adopt the different load safety factors specified in Table 1.

8.1.6 Normal operating loads can be divided into the following three cases.

1.Characteristic extreme load (maximum value of the load combination under normal and extreme conditions);

---S2.LDD10-4 (load level with an exceedance probability of 0.01%, equivalent to approximately 22 hours of occurrence within 25 years);

---S3.LDD10-2 (load level with an exceedance probability of 1%, equivalent to approximately 2200 hours of occurrence within 25 years). S1 can be used for tensile strength verification of steel reinforcement and compressive strength verification of concrete in concrete structures, while S2 can be used for verification of fracture toughness required for steel structures. Stress level verification. S3 can be used for stress relief verification and crack control verification of concrete structures.

8.1.7 The integrated calculation and analysis of floating offshore wind turbine generators shall comply with the provisions of GB/T 47558.

8.2 Load Conditions

8.2.1 The integrated load conditions for the support structure of offshore wind turbine generators shall comply with GB/T 18451.1-2022 and GB/T 31517.1- The provisions of 2022 and GB /Z 44047-2024.

8.2.2 The integrated load design conditions for the support structure of offshore wind turbine generators should include wind conditions and sea conditions with a reasonable probability of occurrence. The DLC is determined by the combination of electrical and other external conditions. Special environmental conditions should also cover specific operating conditions within that environment. Table 2 lists... The minimum load design conditions for the support structure of offshore wind turbines should be considered.

8.5 Seismic Conditions

8.5.1 The time-history load analysis method should be used for the seismic load calculation of the support structure of offshore wind turbine generators, especially for those located in areas with strong seismic activity. Offshore wind farm projects that are significantly affected by earthquakes should take into account the occurrence of earthquakes during normal power generation, the shutdown process caused by earthquakes, and the subsequent ground subsidence. For seismic load conditions, the seismic load conditions should be considered according to Table

5.Seismic load calculations should use seismic motion parameters with a 475-year return period. The load calculation should use 7 sets of ground motion acceleration time histories, of which the number of measured strong earthquake records should not be less than 2/3 of the total.

8.5.2 The loads on the blades, drive train, and structural components of offshore wind turbine generators can be verified based on the load parameters obtained from a 50-year return period earthquake. The main components should maintain linear elasticity during calculation.

8.6 Integrated Load Analysis of Floating Offshore Wind Turbine Generators

8.6.1 In addition to considering the working conditions in Table 2, the integrated load analysis of the support structure of floating offshore wind turbine generators should also comply with the conditions in Table 6 for floating offshore wind turbine generators. Special design load conditions for the support structure of the wind turbine generator set. In DLC

4.3 operating condition 8.6.2, when the actual sea state exceeds the design sea state boundary for normal power generation of the floating offshore wind turbine, the control... The system executes the wind turbine generator protection shutdown process. In DLC2.6, the failure of the monitoring or control system is considered, leading to the floating... The situation where offshore wind turbines operate and generate electricity beyond the sea state boundaries designed for normal power generation.

8.6.3 The integrated load simulation of floating offshore wind turbine generators should consider the instantaneous failure of a single mooring cable or tension tendon, as well as the relationship between the floating foundation and the load. The motion and load response of the mooring system after reaching a new equilibrium state. Specific settings are shown in Tables 6 for DLC9.1, DLC10.1, DLC9.2, and... DLC10.2.

8.6.4 For floating offshore wind turbine generators with multiple compartments, all phases should be carried out according to DLC

10.3 in Table 6. Analysis of water ingress into the closed compartment.

8.6.5 The robustness design of floating foundation structures and anchoring systems should consider environmental load combinations that occur once every 500 years. Specific settings should refer to... According to Table 6, DLC10.4.

8.6.6 For floating offshore wind turbine generators, the movement of the foundation structure and the yaw error of the wind turbine generator should be considered. Specific settings are detailed in Table 6. Chinese DLC 9.1~DLC 10.3.

8.6.7 For non-redundant anchoring systems, DLC9.1, DLC9.2, DLC10.1, and DLC

10.2 can be ignored, but in this case, additional [features/equipment] are required. Additional safety factor should be determined in conjunction with the non-redundant mooring system and mooring materials.

8.6.8 The integrated load analysis of floating offshore wind turbine generators should be combined with the selection of the gust model period based on the inherent motion period of the floating foundation. For a long-period wave model considering swells, please refer to Appendix O of GB /Z 44047-2024 for details.

8.6.9 Integrated load simulation of floating offshore wind turbine generators; the simulation duration for a single operating condition should ideally reach 3 hours. This should be based on the single operating condition simulation duration. The length is adjusted appropriately based on the average wind speed and Hs under the given reference period in the design data.

8.6.10 The integrated load simulation of floating offshore wind turbine generators should consider the influence of second-order wave loads. If sensitivity analysis proves otherwise... The effect of second-order wave loads is relatively small and can be ignored.

8.6.11 The effects of high and low tide changes on the pretension of the mooring system and the natural period of the floating foundation, as well as the effects on the wave action of the floating foundation, should be considered. The effect of load.

8.7 Integrated Load Post-processing

8.7.1 The integrated load post-processing of offshore wind turbine generator sets should include the load post-processing of the rotor-nacelle assembly and the supporting structure.

8.7.2 Detailed ultimate strength design analysis of the rotor-nacelle assembly and support structure of offshore wind turbine generators should be performed using the finite element method or other methods. Appropriate methods should be used, and the load can be obtained from the statistical matrix results of the limit load of the corresponding component.

8.7.3 The ultimate load statistics can be performed using the method of GB/T 18451.1-2022.

9.1 General Rules

9.1.1 Integrated design should take into account the safety and economy of the supporting structure.

9.1.2 The integrated design should adopt the limit state design method based on probability theory and expressed by partial coefficients. The design expression is shown in formula (2).

9.1.3 The support structure of offshore wind turbine generators should be designed based on integrated load.

9.1.4 The support structure of offshore wind turbine generators shall be designed according to the ultimate limit state and normal operating conditions...