GB/T 47558-2026Wind energy generation systems - Guide for the integrated analysis of floating offshore wind turbines (English PDF)

5.2 Sea State

5.2.1 Water level data should include the relationship between the engineering site and the datum, water depth, tidal characteristics, high tide level, low tide level, tidal range, and duration of rising and falling tides. Values and design tide levels for different return periods.

5.2.2 Salinity, density and temperature of seawater.

5.2.3 Ocean current data should include stratified current velocities and directions at different return periods for different locations within the site area.

5.2.4 Wave data should include wave direction, wave height, and wave period at different return periods, and should preferably be described in the form of wave scatter plots, contour lines, etc. High-period joint distribution characteristics.

5.2.5 Marine biological data should include marine biological growth thickness, density, distribution characteristics, etc.

5.2.6 Sea ice data should include the ice-free period, ice-free water level, ice rink area distribution and movement characteristics, and different reproduction numbers for the sea area where the wind farm is located. The design parameters include ice thickness and mechanical properties.

5.3 Combined wind and wave distribution

5.3.1 The statistical content of the combined wind and wave distribution mainly includes.

a) The combined distribution direction of wind and waves should be statistically analyzed by sector, with each sector not exceeding 30 degrees.

b) Statistically analyze the probability distribution of wave height and wave period in different directions at certain wind speed intervals;

c) Calculate the joint probability of wind and waves in all directions at certain wind speed intervals.

5.3.2 The wave height difference should not exceed 0.5m, and the period difference should not exceed 0.5s; the wind speed range should cover both the incoming and outgoing wind speeds. The speed interval should not exceed 2 m/s, and preferably not exceed 1 m/s.

5.4 Engineering Geology Geological data should include seabed topography, rock (soil) layer distribution and lithological characteristics and mechanical properties of each layer, seismic motion parameters and corresponding data. The basic intensity of the earthquake.

5.5 Wind Turbine - Nacelle Components, Tower and Control Systems

5.5.1 The information on the wind turbine-nacelle assembly and tower should include.

a) Security level;

b) Wind turbine cone angle and drive shaft pre-tilt angle;

c) Blade or equivalent airfoil parameters;

d) Materials, dimensions, mass, center of gravity, and moment of inertia of blades, hubs, nacelles, and towers;

e) Hub center height;

f) Cabin tilt angle and acceleration requirements;

g) Thrust curve and power curve.

5.5.2 Control system data should preferably include.

a) Control system type and main parameters;

b) Control system logic and strategies.

5.6 Floating Foundation Structure Floating foundation information should include the following.

a) Master Dimensions and General Layout Drawings;

b) Structural layout and material properties;

6.1 Calculate the load

6.1.1 The input loads for integrated calculation and analysis should include driving loads, gravity loads, aerodynamic loads, wave loads, flow loads, and marine organism attachment. The load should be considered, and sea ice load, seismic load, impact load, etc. should also be taken into account.

6.1.2 The driving load shall include the torque control load of the generator and converter, the driving load of yaw and pitch, and the mechanical braking load.

6.1.3 Aerodynamic loads should take into account the effects of tip losses, hub losses, tower shadow effects, and aeroelasticity. The motion of floating foundation structures should also be considered. The impact.

6.1.4 Wave Load.

a) Wave loading takes into account all potential effects, including water depth, marine organism attachment, structure type, scale, shape, and response characteristics;

b) Wave loading should take into account the effects of nonlinear waves and the rise of the free wave surface;

c) For floating foundations with a large waterline (such as barges), the impact of waves should be considered, and the impact load should be determined by calculation. Determined by computational fluid dynamics methods, water tank tests, or relevant regulations.

6.1.5 Flow Load.

a) The flow load on a floating foundation structure can be determined using the overall coefficient method, Morrison's formula, or a water tank test;

b) When using the Morrison method, the influence of auxiliary components should be considered;

c) The effects of wave-current coupling and vortex-induced vibration should be considered when considering flow loads.

a) Seismic action shall be determined in accordance with the provisions of NB/T 11600;

b) Sea ice load shall be determined in accordance with the provisions of NB/T 11084;

c) The impact of marine life should be adjusted according to the marine life situation, including the mass and buoyancy of the floating foundation structure and anchoring system, and the dynamic submarine cable model. For the diameter and effective drag force diameter, when no actual measured data is available, the density can generally be taken as 1300kg/m3~1400kg/m3;

6.2 Calculation requirements for working conditions and load combinations

6.2.1 The integrated calculation and analysis should select the controlling load case or the load case of design concern, and the load combination should comply with GB/T 31517.1 In accordance with the provisions of GB /Z 44047.

6.2.2 Load combination coefficients may not be considered during integrated calculation and analysis.

7.1 General Requirements

7.1.1 The integrated computational analysis system should include simulation modules for aerodynamics, hydrodynamics, structure, and control, and the modules should be able to transfer data to each other. And exchange function.

7.1.2 The calculation model should accurately simulate the wind turbine-nacelle components, tower, floating foundation structure, anchoring system, dynamic submarine cables, etc., and can be based on calculations. The analysis should be appropriately simplified based on type, purpose, and structural features.

7.1.3 The calculation scope of the model should cover the floating offshore wind turbine generator and the motion range of the entire system.

7.1.4 The element size of the computational model should meet the accuracy requirements and can be determined based on sensitivity analysis; the element division should be mutually consistent when calculating different modules. Coordination. When using a meshless method, the initial particle distribution and quantity should be evaluated.

7.1.5 Multiple methods should be used to verify the model during modeling to ensure its accuracy.

7.2 Aerodynamic and Hydrodynamic Models

7.2.1 Aerodynamic Model.

a) Wind models include steady-state models, turbulent models, and gust models. The model type and parameters are determined according to the corresponding calculation conditions.

b) Blade aerodynamic modeling can be built using blade element momentum theory, actuation line theory, generalized dynamic wake, computational fluid dynamics (CFD), etc. Methods to characterize its microscopic aerodynamic properties;

c) When using the CFD method, the mesh size of the aerodynamic model should be determined based on the aerodynamic load model of the blade, and the mesh accuracy should be sensitive. Intuitive analysis.

7.2.2 Hydrodynamic model.

a) The wave model can use either regular or irregular wave types, and the wave type should be determined with reference to the actual observation values of the engineering area. parameter.

b) When using regular waves, select an appropriate wave theory based on wave steepness and water depth; when using irregular waves, refer to the actual observations of the engineering area. Wave spectrum was used for measurement.

c) The ocean current model should be able to characterize the velocity profile of the engineering area; the velocity profile should be based on actual observations or subsequently reported data. Dragging force system The number or flow load coefficient should be determined through towed water tank model tests or wind tunnel model tests.

d) Hydrodynamic models of floating foundations and anchoring systems can be developed using methods such as Morrison's formula, potential flow theory, and CFD. Wave-current coupling Complex hydrodynamic processes with significant viscous effects, such as vortex-induced vibration/vortex-induced motion and wave impact, can be studied using CFD methods. calculate.

e) When performing hydrodynamic calculations based on potential flow theory, the mesh size for the wetted surface should preferably not exceed 2m and 1/7 of the wavelength. When drawing the free surface mesh, ensure a sufficient number of meshes to accurately capture wave features.

f) When performing hydrodynamic calculations using the CFD method, sufficient space should be provided between the wave-generating boundary and the structure, and a reasonable [property] should be placed before the outflow boundary. Wave damping methods should be implemented to eliminate the influence of reflected waves; simultaneously, a two-phase flow method should be used when simulating aerodynamic and hydrodynamic processes, combined with boundary conditions. Surface tracking and capture algorithms are used to characterize complex water surface processes such as wave breaking.

g) When using the CFD method, the mesh size of the hydrodynamic model should be determined based on the water flow and wave conditions and the dynamic characteristics of the floating foundation structure. The grid accuracy sensitivity analysis was then conducted.

7.3 Structural Model

7.3.1 The structural model realistically reflects the mass distribution, center of gravity, stiffness, and damping characteristics of each component, mainly including the wind turbine-nacelle assembly. Models include component models, tower structure models, floating foundation structure models, mooring system models, and dynamic submarine cable models.

7.3.2 Structures with small deformation, structures whose characteristic frequencies are far from the wave-induced and wind-induced frequencies, and structures whose deformation has little impact on the overall system response. A rigid body model can be used.

7.3.3 The wind turbine-nacelle assembly model should include components such as blades, hub, and nacelle. The deformation effects on the blades and tower structure should be considered. Other components... Rigid body simulation can be used for the components. In the calculation and analysis of floating foundation structures and anchoring systems, lumped mass and inertial properties can be used. The internal components of the wind turbine-nacelle assembly are simplified.

7.3.4 Flexible blades and tower structures should preferably use a beam model, and the mass, stiffness, and damping ratio of each node should be defined.

7.3.5 Floating foundation structures can adopt rigid body models. When the overall system is subjected to high-order wave forces, blade passing frequencies, generator rotation frequencies, etc. When the excitation is relatively sensitive, or when the floating foundation structure itself is large in size and has significant flexibility, the elasticity of the floating foundation structure should be evaluated.

7.3.6 The mooring system model should include mooring cables, mooring accessories, etc., and preferably include anchoring foundations, and take into account the interaction between the mooring cables and the seabed. Seabed models should be able to characterize seabed stiffness, friction, and scour. This is especially important when considering the dynamic response of towers, floating foundations, and mooring cables. In this case, the mooring connection device and anchoring foundation can be simplified.

7.3.7 When considering the influence of anchorage foundations on the motion response of anchoring systems and floating foundation structures, the geological parameters of the anchorage points should be taken into account. And the soil-anchoring interaction relationship, and select appropriate characterization methods such as equivalent springs.

7.3.8 Mooring cables and mooring accessories, tension tendons, and dynamic submarine cables can be modeled using methods such as the finite element method. Their dimensions and stiffness should be accurately simulated. Mass distribution, hydrodynamics, damping, friction, deformation, and initial tension.

7.4 Control Model

7.4.1 The control system should include blade pitch control, torque control, safety control, yaw control, and should preferably consider vibration control or dynamic ballast.

7.4.2 The controller can be modeled using dynamic link libraries or custom programs.

8.1 General Requirements

8.1.1 Integrated calculations should be constructed by selecting appropriate aerodynamic, hydrodynamic, structural, and control models based on the analysis objectives and requirements. Integrated analysis model.

8.1.2 The integrated calculation and analysis should adopt the time history analysis method.

8.1.3 When a rapid assessment of a floating offshore wind turbine is required, a simplified method can be used for integrated calculation (see 8.3.4).

8.1.4 The integrated calculation results should include, depending on the calculation purpose. blade loads and deformations, aerodynamic performance, mechanical system loads and vibrations, and tower loads. Loads and deformations, motion and loads of floating foundation structures, dynamic submarine cable response, and anchoring system response.

8.2 Calculation Methods and Requirements

8.2.1 When calculating aerodynamic loads based on blade element momentum theory, generalized dynamic wake, actuation line model, CFD, etc., the following provisions shall be met.

a) When using blade element momentum theory to calculate aerodynamic loads, the blade is divided into multiple blade elements, and the aerodynamic forces of each blade element are calculated independently. Turbulence and dynamic stall effects are handled by combining momentum balance with a wake model, and coupled in real time with the motion of a floating base. The inflow velocity distribution is updated using the state-inflow model to indirectly correct the leaf element angle of attack.

b) When using the generalized dynamic wake model, the evolution of the wake momentum is described by time-delay differential equations, thus correcting the steady-state wake of the leaf element momentum theory. Flow assumption. For low-frequency oscillations of floating foundations, a wake convection time delay effect is introduced to correct the inflow velocity, and this is combined with a dynamic stall mode. Type to handle aerodynamic hysteresis and abrupt changes at large angles of attack.

c) When using the actuation line model, the blade is simplified as a linear volumetric force source, and the force is projected onto the CFD mesh through a Gaussian-distributed volumetric force. The mesh is refined near the actuation line to resolve the blade wake, and coarsened in the far field. The floating fundamental motion is realized using dynamic meshing technology. Currently, it is necessary to explicitly couple and solve the flow field and structural motion step by step.

d) The aerodynamic loads on towers and floating foundations can be simplified by using the drag coefficient method, discretizing them into multiple segments, and assigning empirical drag coefficients to each segment. Force coefficients are calculated by assuming a quasi-static state and neglecting vortex-induced vibration, focusing only on the average wind load.

8.2.2 For components with a diameter or width less than or equal to

0.2 times the wavelength, the wave current load can be calculated using the Morrison formula and should conform to... According to NB/T 11084, for components with a diameter or width greater than

0.2 times the wavelength, wave loads can be calculated using potential flow theory superimposed with Morrison's formula. The viscosity effect is calculated using a formula.

8.2.3 Calculations based on potential flow theory.

a) The viscous effect can be considered using an additional damping coefficient matrix or the Morrison formula;

b) The additional damping coefficient matrix can be determined through pool testing or validated numerical simulation;

c) The influence of second-order wave forces should be considered;

d) Tension leg type floating foundation structure systems should consider third-order or higher wave forces;

e) When performing frequency domain analysis, the wave frequencies should cover the entire wave frequency range, and the fineness of the wave frequency division near the resonance region should be increased. It reflects the maximum response amplitude.

8.2.4 Calculation based on CFD method.

a) The accuracy and rationality of the simulation of the background wave field and flow field were verified by using open-field wave generation and flow generation.

b) Sufficient space shall be provided between the wave-generating boundary and the structure to ensure the elimination of the influence of reflected waves.

c) Set up appropriate wave-damping methods in front of the outflow boundary to avoid wave reflection affecting the calculation results.

d) Sufficient mesh count should be set near the free surface to ensure accurate capture of wave characteristics; boundary layer mesh should be set on the object surface. The grid transition should be optimized, and the grid size should be determined through sensitivity analysis.

e) It is advisable to use the Reynolds-mean-turbulence model to simulate turbulence effects, or to use large eddy simulation techniques to analyze turbulence.

8.3 Integrated Computing

8.3.1 Integrated computing can employ fully coupled, subsystem coupled, or simplified methods, depending on the analysis objective, the object of interest, and the integrity of the data. For the integrated calculation and analysis process, please refer to Appendix A.

8.3.2 The fully coupled method should construct a comprehensive multiphysics model of the floating offshore wind turbine and the marine environment, and at each time step... Simultaneous solution of aerodynamics, hydrodynamics, structure and control.

8.3.3 The subsystem coupling method can calculate aerodynamic loads, hydrodynamic loads, motion response, and control command feedback separately, and iteratively solve... Solution. Implement the interaction between the subsystems (see Figure 1). Consistent model parameters and bidirectional data transfer should be ensured between subsystems, and the results should be correct. A perfect match.

8.3.4 The following methods can be used to simplify calculations.

a) The subsystems are coupled in one direction and data is transferred one-way. The loads generated by the aerodynamic and hydrodynamic subsystems are used to calculate the floating base. Basic motion response;

b) When detailed information is lacking, select existing information on wind turbine-nacelle components of the same or similar type to create an equivalent model;

c) Ignoring the effects of driving loads and the control system, aerodynamic loads are applied using time-history curves, wind force coefficients, or steady forces, etc.

d) The full matrix quadratic transfer function is not considered for hydrodynamic loads; the second-order hydrodynamic loads are solved using the Newman approximation method.

e) Ignoring the effects of nonlinearity in the mooring system, the calculation is performed using the restoring force matrix, and dynamic loads are not considered.

f) The effect of structural elasticity is not considered for floating foundation structures.

8.4 Reasonableness Analysis The integrated calculation and analysis results should undergo regularity and rationality analysis of the value range, including blade deformation and load, tower deformation and load. The load, cabin motion, floating foundation structure motion, and anchoring system stress, etc.

8.5 Results Verification

8.5.1 Verification of analysis results can be achieved through equilibrium condition estimation, comparison of analytical solutions, comparison of results from different software, engineering analogy, and model testing. Evidence and other methods.

8.5.2 Integrated calculation and analysis should be verified in conjunction with model test results under equivalent conditions, including tower load, nacelle motion, and floating. Hydrodynamic characteristics and motion response of the foundation structure, response load of the anchoring system, etc.

9.1 Results Compilation

9.1.1 Blade loads and deformations should include blade root loads, blade tip deformations, and air gap height; aerodynamic performance should include power generation and rotor thrust. Mechanical system loads and vibrations should include six degrees of freedom loads on the engine room and translational accelerations in three directions, as well as generator torque, yaw, and pitch control. Braking load and mechanical braking load.

9.1.2 Tower loads and deformations shall include tower bottom loads, loads on other critical sections, and tower deformation.

9.1.3 The response and load of the floating foundation structure shall include the six degrees of freedom motion of the floating foundation structure, the air gap height and the load.

9.1.4 The dynamic submarine cable response should include the minimum bending radius of the dynamic submarine cable, the load on the critical section, the dynamic submarine cable-platform interference and bottoming out, and Water discharge. The tension at any point on the dynamic cable should not exceed the maximum allowable tension corresponding to the bending radius of that point.

9.1.5 The response of the anchoring system shall include the force on the anchor chain or tension tendon, the pull-out force at the anchor point, and the length of the horizontal chain.

9.1.6 The integrated calculation results should preferably use contour lines, cloud maps, vector maps, distribution curves, change process lines, characteristic values, and columns of characteristic areas. Tables and similar items can be dynamically displayed using animation.

9.1.7 For the analysis results of time processes, the maximum, minimum, mean, and standard deviation of each physical quantity should be extracted. An envelope diagram should be drawn, and accompanying data should be provided. The temporal process of combining feature points is presented to show the calculation results and the frequency domain features.

9.2 Analysis and Evaluation This paper analyzes and evaluates the operational behavior of each component of a floating offshore wind turbine and its dynamic submarine cable under various calculated operating conditions. The methods for price analysis and evaluation can include analogy or comparison. Evaluation content includes, but is not limited to.

a) Analyze the correlation between the frequency characteristics of the object and the natural vibration characteristics of other components, wave frequency, and wind load frequency;

b) Power generation, rotor thrust, nacelle acceleration, nacelle tilt angle, control system effectiveness, and robustness of floating offshore wind turbine generators. Rod properties, tower bottom load, motion response and mooring stress, blade tip air gap, clearance between blade tip and tower, etc.