Response Of Floating Offshore Wind Turbine Research Articles

Dynamic response of multi-unit floating offshore wind turbines to wave, current, and wind loads

Motion of a multi-unit wind-tracing floating offshore wind turbine (FOWT) to combined wave–current and wind is obtained in the frequency-domain. The linear diffraction wave theory with a Green function for small current speeds and the blade-element momentum method are used for the hydrodynamic and aerodynamic analysis, respectively. A finite-element method is coupled with the hydrodynamic and aerodynamic equations to obtain the elastic responses of the FOWT to the environmental loads. The wind-tracing FOWT consists of three 5 MW wind turbines installed at the corners of an equilateral triangular platform. The platform is connected to the seabed through a turret-bearing mooring system, allowing the structure to rotate and face the dominant wind direction; hence, the multi-unit FOWT is called the wind-tracing FOWT. In this study, rigid-body responses of the wind-tracing FOWT to waves and wind are compared with those to combined wave, current, and wind loads for several current speeds and various wave heading angles. For a chosen current speed and wave heading angle, hydro- and aeroelastic responses of the wind-tracing FOWT to combined waves, current, and wind are obtained and compared with those of the rigid structure. Discussion is provided on the effect of the wave–current interaction on the motion and elastic responses of the wind-tracing FOWT. The numerical results show that under the rated wind speed, the motion of the wind-tracing FOWT is mainly governed by the wave-induced hydrodynamic forces and moments and the presence of current results in larger elastic motion of the FOWT to the environmental loads.

The Probability of Ship Collision during the Fully Submerged Towing Process of Floating Offshore Wind Turbines

As global warming intensifies, the development of offshore wind farms is swiftly progressing, especially deep-water Floating Offshore Wind Turbines (FOWTs) capable of energy capture in deep-sea regions, which have emerged as a focal point of both academic and industrial interest. Although numerous researchers have conducted comprehensive and multifaceted studies on various components of wind turbines, less attention has been paid to the operational stage responses of FOWTs to wind, waves, and currents and the reliability of their structural components. This study primarily employs a theoretical analysis to establish mathematical models under a series of reasonable assumptions, examining the possibility of collisions between FOWT transport fleets and other vessels in the passage area during the towing process. Using the model, this paper takes the Wanning Floating Offshore Wind Farm (FOWF) project, which is scheduled to be deployed in the South China Sea, as its research object and calculates the probability of collisions between FOWTs and other vessels in three months from the pier near Wanning, Hainan, to a predetermined position 22 km away. The findings of the analysis indicate that the mathematical model developed in this study integrates the quantities and velocities of navigational vessels within the target maritime area as well as the speeds, routes, and schedules of the FOWT transport fleet. By employing statistical techniques and geometric calculations, the model can determine the frequency of collisions between various types of vessels and the FOWT transport fleet during the transportation period. This has substantial relevance for future risk assessments and disaster prevention and mitigation measures in the context of FOWT transportation.

Research on dynamic response prediction of semi-submersible wind turbine platform in real sea test model based on machine learning

The motion response of floating offshore wind turbine (FOWT) platform is closely related to its safety, and model test is the most direct method to fully study its dynamic characteristic behavior. In this paper the dynamic response of intermediate-scale physical semi-submersible FOWT model test under real sea environmental loads is studied and compared with the numerical model dynamic response, demonstrating that some limitations of small-scale physical model tests can be overcome, such as the catenary effect of mooring lines. It is found that the nonlinear dynamic characteristics of the physical model under actual marine environmental loads can be captured by the numerical model, which can improve the fidelity of model test data for semi-submersible FOWT structures in the existing literature. The dynamic response database of semi-submersible FOWT under complex wind, wave and current loads was established by using a numerical model with high accuracy, and was used in the prediction research of different machine learning algorithm models such as Genetic Algorithm optimization Back Propagation neural network (GA-BP), Support Vector Machine (SVM) and Gaussian Process (GP). The research shows that the relationship between the environmental load and the dynamic response of FOWT can be established by using the machine learning model, in which the number of samples has a significant impact on the prediction of the mooring line tension, and the research on the three algorithm models shows that GP performs significantly better than GA-BP and SVM in predicting the mean value of surge, pitch and mooring line force. For the dynamic response prediction of mooring line tension, GP model can get better results. In the future, this method will become an important method to predict and monitor the dynamic response of FOWT.

Hydrodynamic studies of a 15 MW semi-submersible FOWT to assess the suitability of the inclusion of a damper system

Floating Offshore Wind Turbines (FOWT) can exploit the high energy density found in the offshore environment, with turbines now reaching up to 15 MW in size. At the same time, however, the energetic environment and the massive size of the device present significant challenges in the motion stabilization and mooring system. To overcome these challenges, a tuned mass damper (TMD) has been considered for integration in the FOWT for peak motion reduction. This paper investigates the baseline responses including motion, dynamic response, and tensile loading of the mooring line for a 15MW FOWT on a semi-submersible platform without TMD to identify the damageable motion and the impacts of the TMD on the motion response under wave-wind environmental loadings. The comprehensive analysis is conducted in a package for the dynamic analysis of offshore marine systems, named as Orcaflex. The dynamic and motion characteristics of the 15MW FOWT are analysed and compared under different environmental parameters. The wave and wind parameters are quantified by the 20-years statistical data of the Celtic Sea including both operational and extreme conditions (with a 50-year return period). Subsequently, the key parameters of TMD are investigated by configuring different combinations of mass, damping coefficients and stiffnesses. The preliminary results of the study show that the TMD system can successfully mitigate extreme motion characteristics, however this is strongly dependent on damping properties. Unsuitable TMD designs may increase the motion responses of FOWT and the tensile loading on the mooring line. Therefore, the TMD properties have to be adjusted based onsite environmental conditions). With this consideration, an active TMD with changeable damping properties will be conducted in future research.

Structural vibration control of spar-buoy floating offshore wind turbines

Floating offshore wind turbines (FOWTs) have complex dynamics problems and strong coupling effects within their entire systems, and they are sensitive to winds and sea waves that may cause structural fatigue damages and power production fluctuations. Structural vibration control is a promising way to reduce FOWT responses, but most previous studies focused on linear control strategies with the limitations of requiring large strokes and having narrow effective frequency bandwidth. Nonlinear energy sinks (NESs) have emerged as an alternative to overcome the above limitations of linear control methods. In the present study, an OC3-Hywind spar-buoy FOWT is selected as a prototype structure for developing an in-house model to investigate its associated aerodynamics, hydrodynamics, and structural dynamics. The wind turbine blades and tower are modelled by three-dimensional Euler-Bernoulli beam elements and the floater is assumed as a rigid body. The blades’ pre-twist, pitch, and rotating angles are also considered to develop the system’s time-varying mass, stiffness, and damping matrices. The nonlinear quasi-static model is adopted to calculate the forces generated by the mooring cables. The straightforward and efficient in-house model is validated against FAST. Subsequently, a bistable track NES with a profile combining both negative second-order and positive fourth-order terms is proposed, designed, and incorporated into the model to mitigate FOWT responses under two investigated environmental conditions. Results show that the in-house model is of high accuracy in estimating dynamic characteristics and responses of FOWTs, paving the way for preliminary design and analysis of FOWTs with different platform types. Moreover, the bistable track NES can effectively control the fore-aft displacements at the tower top with practical strokes.

Wave power extraction by Multi-Salter's duck WECs arrayed on the floating offshore wind turbine platform

Integrating a floating offshore wind turbine (FOWT) and an array of wave energy converters (WECs) can be suggested as a proper new hybrid concept with the aim of more energy harvesting and lower total energy cost. This paper proposes the new composition of a floating braceless semi-submersible platform and an array of Salter's duck (SD) WECs. First, a comparison of the numerical results and experimental data of the hydrodynamics response of FOWT and the single SD WEC response are presented and discussed. Then, the performance of three-hybrid FOWT-Multi-Salter's Duck (FOWT-MSD) systems with 12SD, 15SD, and 18SD WECs has been investigated under different wave periods and wave heights. In the wave period of 6–9 s, 12SD absorbs more power than 15SD and 18SD. From T = 9–11 s, all three systems have the same absorbed power. For wave periods above 12 s, 15SD and 18SD have higher absorbed power than 12SD. No clear trend was observed for wave periods below 6 s. The effect of wave direction shows that at lower wave heights, maximum absorber power belongs to FOWT-12SD under zero wave direction. In contrast, increasing wave heights leads to a smaller difference between the three-hybrid systems at different wave directions.

Dynamic Response of 15 MW Floating Wind Turbine With Non-Redundant and Redundant Mooring Systems Under Extreme and Accidental Conditions

AbstractThis work focuses on examining the dynamic behavior of large floating offshore wind turbine (FOWT) exposed to extreme (wind and wave with 50-year return period) and accidental (mooring line breakage) loadings. The FOWT considered is 15 MW reference turbine supported on semi-submersible platform stationed using catenary moorings. As the mooring configuration greatly affects the response of FOWT, two different mooring configurations namely non-redundant (three-line) and redundant (six-line) systems were studied and compared. The coupled multi-body dynamic system was solved using Openfast. When simulating the mooring line failure, both the operating and extreme loading conditions were considered. Failure of one mooring was considered at a time. The response of the coupled system due to breakage of the mooring indicates high displacements in surge and sway directions in comparison to the intact system especially for the non-redundant mooring system. Furthermore, change in platform yaw angle and increased tension in the other intact mooring lines were observed. The findings from this study will be helpful in accidental limit state design and preventing failure of similar large FOWT systems. In addition, insights into using non-redundant and redundant mooring configurations for such large structures with respect to extreme and accidental loadings were also discussed.

Research on coupled dynamic characteristics of Floating Wind Turbine under complex environment

The fully coupled aerodynamic-hydrodynamic-mooring numerical model of floating offshore wind turbine(FOWT) has been established. The complex conditions such as second-order wave force, full-field turbulent wind, and mooring break have been taking into account. Using OrcaFlex and FAST to calculate the dynamic response of FOWT under the combined action of wind, wave and current. The time-domain response of floating foundation, mooring tension, blade root contact force, aerodynamic power, and wind rotor thrust are obtained. And the effect of the turbulent wind and mooring break at different positions on the FOWT are studied. The results show that compared with the platform motion and mooring tension, the aerodynamic power and rotor thrust are more sensitive to the turbulent wind, and there are fluctuations in amplitude and multiple peaks in the frequency spectrum. Compared with the leeward side, the mooring break on the windward side is a more dangerous situation, and it is easy to cause the collapse of platform and the break of the remaining mooring. The mooring break on the leeward side is relatively safe, and it will produce a drift in the sway direction, and have little impact on the safety of the wind turbine.

Research and numerical analysis of floating offshore wind turbine based on a novel extended tuned mass damper

Offshore wind turbines will be developed from shallow water to deep water to meet the rapid growth of wind power generation. Floating offshore wind turbine (FOWT) faces complex load challenges, which endanger its safety and service life. Hence, it is urgent to develop a novel damping device to improve the stability of FOWT. In this paper, a novel extended tuned mass damper (ETMD) is proposed. On this basis, a linear quadratic regulator is added to realize the design and simulation of the extended active tuned mass damper (EATMD) control system to reduce the surge response of FOWT. Numerical analysis shows that under the control of ETMD, the surge response of the tower is reduced by 73%, and the frequency modulation width is increased by 55%. Here, under the control of EATMD, the displacement, velocity, and acceleration of the surge response of the tower are decreased by 47.0%, 30.7%, and 24.2%, respectively.

Transient response reduction of floating offshore wind turbine subjected to sudden mooring line failure

Floating offshore wind turbine (FOWT) is subjected to different dynamic loads during its lifetime. It is essential to ensure the safety of FOWT against these loads to avoid the economic losses. In the past, a majority of the studies focused on reducing the effect of dynamic loads due to wind and waves. This paper explores the application of a tuned mass damper (TMD) for reducing the transient response of FOWT during the mooring line failure. The FOWT is subjected to sudden loads when there is a mooring line breakage. The response control of FOWT during such an event is of immense importance to avoid the catastrophic failure. Although TMD is usually designed for vibration reduction in a steady state, this work focuses on transient response reduction. The investigations are carried out for a case where TMD is placed in the nacelle of FOWT. A reduced-order model is used for the TMD design. An optimum TMD is obtained by minimizing the H∞ norm of the system response when subjected to external disturbances. The designed TMD performance is assessed by carrying out a coupled nonlinear dynamic analysis using aero-hydro-servo-elastic code, OpenFAST. Three different environmental conditions corresponding to below-rated, near-rated, and near-cut-out wind speeds are considered for the analysis. The effectiveness of the TMD is assessed for the scenario of single, double, and triple mooring line failure. The performance indices, defined in terms of peak, root mean square, and standard deviation of the FOWT responses are evaluated for each of the cases. The designed TMD is found to be advantageous for reducing the transient response of FOWT during the mooring line failure. Therefore, the TMD can be effectively used for transient response reduction and enhancing the safety of FOWT in the event of accidental mooring line failure.

An equation-based method for fully coupled analyses of floating offshore wind turbine based on Modelica

This paper presents a fully coupled aero-hydro-servo-elastic method to simulate floating offshore wind turbines (FOWT) based on Modelica language and AeroDyn co-simulations. The main features of this method are as follows. (1) The features of Modelica language (equation-based, object-oriented, and hierarchy structure) afford extreme flexibility and efficiency in the modeling process, and wind turbine structures or theoretical methods can be easily upgraded or replaced. (2) AeroDyn, a relatively precise aerodynamic load calculation module, is integrated into the system; thus, the model is more accurate than the previous Modelica library in calculating the responses of FOWTs. First, this paper introduces the theory of the proposed model in Modelica and AeroDyn module to calculate offshore FOWT response. Second, the implementation method for Modelica with AeroDyn is introduced. A dynamic link library (DLL) is programmed as the channel for exchanging data, and a controller to coordinate the stepping relationship between Modelica and AeroDyn is established. Third, code-to-code comparisons are performed based on International Energy Agency (IEA) Wind Task 23 Subtask 2. The results show excellent agreements between the proposed method and FAST in predicting dynamic responses of the rotor, tower, platform, and mooring system under both steady and turbulent winds combined with wave conditions. Finally, a case about high altitude work is carried out to demonstrate the flexibility of modeling processes. A single pendulum model constrained at the bottom is used to model the motion of the worker at a high altitude, coupled to the motion of a FOWT. The results show that the motion along the Y-axis is effectively suppressed as the damping force at the bottom increases, while the suppression is less pronounced on the X-axis. This method comprising the structure properties of blade and time domain potential flow hydrodynamic loads is more complete than the previous method using Modelica language to construct the fully coupled FOWT simulation model. Besides, it provides a more flexible modeling and simulation tool for some engineering practices, such as FOWT combined with fish cages, and FOWT operation and maintenance.

Experimental study on dynamic response of a floating offshore wind turbine under various freak wave profiles

This study performed experimental investigation on the dynamic response of an in-place floating offshore wind turbine (FOWT) under freak wave actions. Based on the method of wave profile modulation, various freak wave profiles embedded in unidirectional Gaussian seas were generated in wave basin and the action of these waves on the FOWT was measured and analyzed, which has not been done before. The motions of FOWT were analyzed in time domain as well as time-frequency domain. The effect of freak wave parameters on FOWT motions was addressed, i.e., freak wave height, freak wave period, large crest, and deep trough. The dynamic response of FOWT was observed as a spike at the occurrence of freak wave in a conventional random wave, where the impact of freak wave can last for 17 spectral peak periods of wave. Data analysis shows that the motions of FOWT increased linearly with the freak wave height. In addition, the occurrence of freak wave induced the coupled effect on surge and pith, which was strengthen with the increase of freak wave height and wave period. Compared to a large crest, a deep trough of freak wave led to stronger motions and was supposed to be a key concern on the safety of the FOWT. The novel findings in this study provided a reference for the design of survival load on a FOWT and benchmarks for validating numerical models.

Coupled rigid-flexible dynamics modeling and validations of floating offshore wind turbine

Floating offshore wind turbine (FOWT) is a complex dynamical system, and reasonable dynamic model is significant to the structural response analysis and reliability evaluation of FOWTs. In this paper, a coupled rigid-flexible modeling method is proposed to predict the dynamic response of spar-type FOWTs and validated by experimental results. The dynamic modeling framework of the method is firstly presented, including the multi-rigid-body (MRB) module and the flexible tower module. The integrated kinematics formulation of MRB module considering the servo control mechanism is derived based on the quasi-coordinates Lagrange's equation. The equation of motion of the flexible tower is established by synthesizing the finite element method (FEM) and Kane's approach. Next, the external loads modules including gravity effects, hydrostatic and hydrodynamic loads, aerodynamic and mooring loads are addressed and incorporated into the equations of motion of the system. The proposed method is then validated against a scaled experiment and full-scale numerical results of FAST, and the aerodynamic performance, the hydrodynamic performance, the MRB module, the flexible analysis module, the mooring system and the servo control mechanism are systematically valuated. The results indicate that the proposed method has a satisfactory ability to predict the dynamic responses of FOWTs under different conditions.

Effect of Mooring Parameters on Dynamic Responses of a Semi-Submersible Floating Offshore Wind Turbine

Based on a new semi-submersible floating offshore wind turbine (FOWT), a coupling aero-hydro-flexible model was established to study its dynamic behaviors, as well as the corresponding mooring system, under complicated sea scenarios. The aerodynamic load, the wave load, the current load, and the mooring load were taken into consideration. To further investigate the influence of the mooring parameters on the floating system, the diameter and the total length of mooring lines, which are the most critical parameters in mooring line design, were chosen to be analyzed. Particularly, five diameters and seven lengths were adopted to establish the FOWT mooring system, and a time-domain simulation was carried out for each cases. Based on the numerical simulations, their influences on the mooring system stiffness and the dynamic responses of FOWT were studied. The results show that the diameter has little influence on the static shape of the mooring line. The mooring system stiffness can be effectively increased by reducing the length and increasing the diameter of mooring lines. Moreover, the surge motion of floating foundation can be effectively controlled by increasing the mooring line diameter and decreasing mooring line length under the rated sea scenario. From this aspect, the dynamic response features of the FOWTs could be improved.

Dynamic Performance Evaluation of an Integrated 15 MW Floating Offshore Wind Turbine Under Typhoon and ECD Conditions

Technology innovation has led to an increase in floating wind turbine size aimed at releasing the pressure on capital cost and increasing its capacity factor. Large-size turbines pose high challenges regarding design with essential structure reliability. The dynamic performance of an integrated 15-megawatt (MW) wind turbine under extreme sea loads is investigated in this paper. Platform motions, mooring system positioning forces, sizeable blades, and tower behaviors are all studied under the targeted typhoon condition and extreme coherent gust with direction change (ECD) wind condition. Potential flow theory is used to analyze the first-order wave load, mean-drift wave load, and second-order difference-frequency wave load on the substructure of the ultra-large 15 MW floating offshore wind turbine (FOWT). The blade element momentum (BEM) theory is adopted for the calculation of the aerodynamic loads on the floating wind turbine, and the finite element method (FEM) is applied to analyze the mooring lines of the floating wind turbine. The results show that the effect of quadratic transfer function (QTF) will significantly increase the dynamic response of FOWT under the typhoon sea state. The ECD wind condition has an influential impact on the motion responses, the axial force of the mooring lines, and structural responses under the normal operating state.

An aero-hydro coupled method for investigating ship collision against a floating offshore wind turbine

Ship collision hazards with floating offshore wind turbines (FOWTs) has been identified and the dynamic responses of FOWT under ship collision scenarios are necessary to be investigated. This paper develops a numerical solver to address the challenge of considering wind-wave loads in the ship-FOWT collision analysis. The user-defined load subroutine, LOADUD, in LS-DYNA is utilized to model the wind, wave and mooring loads. A simplified aerodynamic model considering blade pitch strategy is used and the hydrodynamic loads are calculated based on potential-flow theory with a linear wave kinematic model. The mooring forces are considered with a linearized model. The implementation of the coupled solver is verified by conducting free decay test, wave-only and wind-only analysis, respectively and comparing them with the reference values. Good agreement has been achieved, indicating that the aero-hydro coupling effects can be accurately simulated by the numerical solver. With the developed method and solver, cases of ship collision with a spar-type floating wind turbine are simulated and both local structural deformation and global motions in 6DOF are obtained. The influence of velocity, flexibility of tower, deformability of the ship, wind-wave loads are further discussed. It is found that the impact velocity can greatly affect the structural responses and a high-speed impact can directly lead to tower collapse. By comparing the cases of ship collision with FOWT, and those with fixed-support wind turbine, the flexibility of wind turbine tower is found to rarely influence the energy dissipation under collision scenario of FOWT, while it is important for the collision scenario of fixed-support wind turbine. The wind-wave condition can be more hazardous as a smaller impact velocity can lead to structures collapsing. This is because, even though the structure can withstand the ship collision, the residual strength may not be enough for the following wind loads, which can result in the structure to finally collapse. Additionally, the proposed fully coupled method is used to validate one of the authors’ previous studies, which is a decoupled method regarding the ship-FOWT collision analysis [1]. The external dynamic results from two methods are compared and discussed. Good agreement is reached between two methods for low-velocity impact but for high-speed collision or collisions with serious deformation, limitations of decoupled method can be found because some basic assumptions of them are violated. The proposed method and solver can be used to evaluate the crashworthiness of FOWT during the engineering design phase.

Software-in-the-Loop Combined Reinforcement Learning Method for Dynamic Response Analysis of FOWTs

Floating offshore wind turbines (FOWTs) still face many challenges on how to better predict the dynamic responses. Artificial intelligence (AI) brings a new solution to overcome these challenges with intelligent strategies. A new AI technology-based method, named SADA, is proposed in this paper for the prediction of dynamic responses of FOWTs. Firstly, the methodology of SADA is introduced with the selection of Key Disciplinary Parameters (KDPs). The AI module in SADA was built in a coupled aero-hydro-servo-elastic in-house programDARwindand the policy decision is provided by the machine learning algorithms deep deterministic policy gradient (DDPG). Secondly, a set of basin experimental results of a Hywind Spar-type FOWT were employed to train the AI module. SADA weights KDPs by DDPG algorithms' actor network and changes their values according to the training feedback of 6DOF motions of Hywind platform through comparing theDARwindsimulation results and that of experimental data. Many other dynamic responses that cannot be measured in basin experiment could be predicted in higher accuracy with this intelligentDARwind. Finally, the case study of SADA method was conducted and the results demonstrated that the mean values of the platform's motions can be predicted by AI-basedDARwindwith higher accuracy, for example the maximum error of surge motion is reduced by 21%. This proposed SADA method takes advantage of numerical-experimental method and the machine learning method, which brings a new and promising solution for overcoming the handicap impeding direct use of traditional basin experimental technology in FOWTs design.

Dynamic Response Analysis of a Semi-Submersible Floating Wind Turbine in Combined Wave and Current Conditions Using Advanced Hydrodynamic Models

In this study, advanced hydrodynamic models are proposed to predict dynamic response of a floating offshore wind turbine (FOWT) in combined wave and current conditions and validated by laboratory and full-scale semi-submersible platforms. Firstly, hydrodynamic coefficient models are introduced to evaluate the added mass and drag coefficients in a wide range of Reynolds numbers. An advanced hydrodynamic model is then proposed to calculate the drag force of cylinder in combined wave and current conditions. The proposed model is validated by the water tank tests in the current-only, wave-only and current-wave conditions and is used to investigate the effect of current on the dynamic response of FOWT. Finally, the full-scale semi-submersible platform used in the Fukushima demonstration project is investigated. It is found that the predicted dynamic responses of platform by the proposed hydrodynamic models are improved by the directional spreading function of the sea wave spectrum and show favorable agreement with the field measurement.

Prediction of dynamic response of semi-submersible floating offshore wind turbines by a novel hydrodynamic coefficient model

A novel hydrodynamic coefficients model is proposed for the components of floating offshore wind turbine (FOWT). First, the formulas for evaluation of the added mass and drag coefficient for the components of FOWT are proposed to consider the interaction effects between columns as well as the frequency and amplitude dependencies. The global matrices of hydrodynamic coefficients are then evaluated by the proposed formulas and validated by the experimental data from the forced oscillation test. The predicted dynamic response of FOWT is also validated by the water tank test. Finally, the improvement of dynamic behaviour of the platform by the skirts is investigated. The decrease of amplitude and the increase of natural period for the heave motion of the platform with skirts are successfully simulated by the proposed model.

Prediction of dynamic response of semi-submersible floating offshore wind turbine using augmented Morison's equation with frequency dependent hydrodynamic coefficients

Abstract A fully coupled nonlinear simulation tool using Morison's equation is developed to predict the dynamic response of floating offshore wind turbine (FOWT) system. Water tank tests are conducted to investigate hydrodynamic coefficients and the performance of the simulation tool under different sea states. Three issues are discussed in this paper. First, correction factors for the added mass and drag coefficients are proposed to account for the effects of frequency dependent hydrodynamic coefficients, and the effects of these correction factors on the global matrices are validated by the forced oscillation tests. Then, the effects of the frequency dependent hydrodynamic coefficients and the axial Froude-Krylov force on slender members are clarified by the free decay tests and water tank tests with regular and irregular waves. Finally, the dynamic behavior of mooring system on the fairlead tension is investigated by using quasi-static and dynamic models, respectively. The dynamic responses of FOWT with improved hydrodynamic models agree well with those measured in the water tank tests.