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Dynamic Analysis of Tension Leg Platform for Offshore Wind Turbine Support as Fluid-Structure Interaction
Abstract
Tension leg platform (TLP) for offshore wind turbine support is a new type structure in wind energy utilization. The strong-interaction
method is used in analyzing the coupled model, and the dynamic characteristics of the TLP for offshore wind turbine support
are recognized. As shown by the calculated results: for the lower modes, the shapes are water’s vibration, and the vibration
of water induces the structure’s swing; the mode shapes of the structure are complex, and can largely change among different
members; the mode shapes of the platform are related to the tower’s. The frequencies of the structure do not change much after
adjusting the length of the tension cables and the depth of the platform; the TLP has good adaptability for the water depths
and the environment loads. The change of the size and parameters of TLP can improve the dynamic characteristics, which can
reduce the vibration of the TLP caused by the loads. Through the vibration analysis, the natural vibration frequencies of
TLP can be distinguished from the frequencies of condition loads, and thus the resonance vibration can be avoided, therefore
the offshore wind turbine can work normally in the complex conditions.
Key wordsoffshore wind turbine–tension leg platform–fluid structure interaction–dynamic characteristics–yaw–resonance vibration
... ,, X X X , and 3 rotational DOFs, 456 ,, X X X . Additionally, the system has 2 unknown DOFs which describe the relative rotation of the second body to the first one, 7 X and 8 X , and also 2 known DOFs of rotor spinning, ,and nacelle yaw, . ...
... to 8 4 10 for spring coefficient and a value of 7 3 10 to 8 1 10 for damping coefficient causes a critical region (increased index) for the structure in heave direction. It should be mentioned that in the critical region the system is more likely to be unstable. ...
Stability and dynamic modeling of the floating wind turbine (FWT) is a crucial challenge in designing of the type of structures. In this paper, the tension leg platform (TLP) type FWT is modeled as a multibody system considering the flexibility between the nacelle and tower. The flexibility of the FWT is modeled as a torsional spring and damper. It has 6 degrees of freedom (DOFs) related to the large-amplitude translation and rotation of the tower and 4 DOFs related to the relative rotation between the rotor-nacelle assembly and the tower. First, the nonlinear equations of motion are derived by the theory of momentum cloud based on the conservation of momentum. Then, the equations of motion are solved and the system is simulated in MATLAB. Moreover, the effect of flexibility between the nacelle and tower is investigated via the dynamic response. The stability of the system in three different environmental conditions is studied. Finally, the spring and damping coefficients for the system response to get near to instability are determined, by which the critical region is defined. The simulation results demonstrate the importance of the flexibility between the nacelle and tower on the overall behavior of the system and its stability.
... The design is based on their past experience in the design and fabrication of TLP which takes into consideration the stability of the structure, mooring forces and ease in maintenance. Huang and Zhang (2011) performed dynamic analysis of tension leg platform for offshore wind turbine support as fluid-structure interaction using finite element method. The study showed that the TLP supporting structure for wind turbine has good adaptability at any water depth and it is less affected by the natural vibration characteristics when changing the mooring length and the depth of platform. ...
The performance of offshore wind turbine supported with different configurations of Tension-leg-platform (TLP) are studied for vertical plane motion responses (surge, heave, and pitch) along with the side-to-side, fore–aft, and yaw tower base bending moments. The long-term distribution is carried out using the short-term floating wind turbine responses based on Rayleigh distributions and North Atlantic wave data. The long-term response analysis is performed for the 5 MW TLP-type offshore wind turbine. The study aims at predicting the most probable maximum values of motion amplitudes that can be used for design purposes. The transfer functions for surge, heave and pitch motions of the floater are obtained using the FAST code. The performance of floating structure in the long-term analysis not only depends on the transfer functions but also on the careful selection of design wave spectrum model. Among different theoretical design wave spectrum models, three models are chosen that closely represents the sea states and the response spectrums are computed for these models. As the nature of the response spectrum of the floating structure is analogous with the input wave spectrum model, it can be assumed to have the same probabilistic properties and modeled as a stationary stochastic process. The long-term probability distributions for TLP-type floater configuration for surge, heave and pitch motion amplitudes along with the tower base bending moments are used for design purposes, so as to guarantee the safety of the floating wind turbines against overturning/capsizing in high waves and wind speed. The calculation of the long-term distribution using FAST will help in the preliminary analysis of the performance of floaters in the study of wave-induced response of floaters.
... The oil geological reserves in South China Sea. gravity and high engineering cost (Huang and Zhang, 2011). Bucket foundation is circular plate with skirts and has some advantages, for example, saving investment and iterative use (Larsen, Ibsen, and Barari, 2013). ...
Wu, K. and Fan, Q., 2015. Study on bearing capacity of bucket foundation subjected to horizontal loading. The bucket foundation is one parts of offshore platform and is wearing the wave or wind loading which causes the bucket foundation instability to offshore platform falling. So, the numerical simulation, limit analysis and model test are investigated and compared in order to reveal the bearing capacity of bucket foundation under horizontal loading. Based on the three analysis methods compared, it can be observed that: (1) the results of the three methods are in good agreement. (2) The bucket foundation subjected to horizontal loading is rotation and the center of rotation is located in the two-thirds of embedded depth. Under horizontal load, the coherent spoon plastic zone is formed in the bottom of bucket foundation. And, the wedge plastic zone is formed on both sides of the bucket foundation. While, in the same direction with horizontal load of the barrel side is passive area and larger earth pressure is being because of barreling into foundation soil. On the other side of the foundation is active area, which the foundation is separation with soil.
High‐frequency pressure pulsations are hydraulic phenomena that are frequently observed in pumped storage power stations. These pulsations can propagate through the steel pipes, concrete lining, and the surrounding rock system, which in turn may have detrimental effects on the environment, such as noise pollution, and relocation of the local residents. This paper proposes a vibration‐damping concept that involves wrapping a local soft cushion layer outside the buried steel pipe; this layer could partially eliminate the pressure fluctuations in the headrace tunnel, thereby reducing the ground vibrations caused by the pressure pulsations. In this study, the finite element method was used to model the propagation of vibrations in the surrounding rock and fluid‐filled pipes, including static simulation of the structure, and dynamic simulation of the surrounding rock. The simulation results suggest that adding an appropriate local soft bedding layer can effectively reduce the ground vibrations by more than 60% and the possible surface noise within the standard vertical vibration norms. The inhibitory effect of the soft cushion on the propagation of vibrations is determined by the wrapping angle, thickness, and material of the bedding layer. This effect increases with increasing wrapping angle and thickness of the bedding layer, and decreases with increasing elastic modulus of the material. After the addition of the bedding layer between the steel pipe and concrete lining, the pressure in the inner pipe is primarily borne by the steel lining rather than the coupling of the steel lining, concrete lining, and the surrounding rock. Hence, the thickness of the part of the steel liner in contact with the soft bedding layer should be increased. In addition, the thickness variations in the steel pipe joints should be smooth to avoid stress concentration.
Fixed offshore wind turbines usually have large underwater supporting structures. The fluid influences the dynamic characteristics of the structure system. The dynamic model of a 5-MW tripod offshore wind turbine considering the pile–soil system and fluid structure interaction (FSI) is established, and the structural modes in air and in water are obtained by use of ANSYS. By comparing low-order natural frequencies and mode shapes, the influence of sea water on the free vibration characteristics of offshore wind turbine is analyzed. On basis of the above work, seismic responses under excitation by El-Centro waves are calculated by the time-history analysis method. The results reveal that the dynamic responses such as the lateral displacement of the foundation and the section bending moment of the tubular piles increase substantially under the influence of the added-mass and hydrodynamic pressure of sea water. The method and conclusions presented in this paper can provide a theoretical reference for structure design and analysis of offshore wind turbines fixed in deep seawater.
This paper focus on the global structure strength analysis of a Tension Leg Platform (TLP) based on the design wave approach, the global structural analysis of the Tension Leg Platform is to ensure the hull global structural integrity under design environmental conditions, then to check if the design scheme is feasible. Firstly, a global FEM model of the entire TLP was established, the hull structure was modeled in detail, whilst the deck structure was represented through a simplified deck beam model. A hydrodynamic analysis for operation and extreme conditions were conducted to get the design wave parameters for critical wave loads. Then, wave loads were mapped to the global structure finite element model, the tendons were modeled as spring element which represents 6 degrees of freedom and rotations. Stress responses are computed by SESAM using the design wave approach. Maximum stresses in the form of equivalent stress (von-Mises) are computed for the passage of a wave characterized by height and period. The maximum stresses include the combined effects of static and dynamic loading. The maximum stress and its distribution trends, control elements were obtained by finite element analysis according to critical wave heading, wave periods, wave heights and wave positions. Results and analysis method proposed in this paper can be used as reference for strength analysis of other offshore platforms. Copyright © 2014 by The International Society of Offshore and Polar Engineers.
Dynamics of deep-sea floating wind turbine was analyzed by the computer simulation technology. Firstly the wave dynamics model of floating platform and aerodynamics model of wind turbine based on the generalized dynamic wake (GDW) theory were established. Secondly, the force was loaded on the multi-flexible body dynamics model of wind turbine including "wind rotor -nacelle- tower- mooring system" which was established in FORTRAN. And then the whole model and results were turned into ADAMS model. Taking a 5 MW wind turbine for example, floating wind turbine system was analyzed by multi-field coupling dynamic model. The results show that during operation of the floating wind turbine, its floating platform must withstand great hydrodynamic force, and the dynamic response of the whole structure and fluctuation of power are greatly impacted by the coupling of aerodynamic and hydrodynamic loads.
A novel test system of dynamic stiffness for isolator of large rated load was desiyned. The dynamic mass was simulated by the universal material testing machine. The dynamic load was performed by impact hammer. The system characteristics such as static stiffness and frequency response function were measured. Therefore the corresponding test formula of dynamic stiffness for isolator was derived. A single axle rubber isolator for large wind turbines was used as example. The experiment results show that the novel approach is applicable to the single axle isolator, the test equipment and construction are easily used. The measured dynamic stiffness is close to the theoretical results, it has slight error in the low frequency range. The method is convenient and practical, and meets the engineering needs.
This paper presents the research and development of a special self-contained Inclinometer based on the requirement of offshore platform monitoring. The device records the anchors inclination completely and accurately, providing information for stress analysis of the anchor chain. Laboratory calibration, platform movement simulation experiment, and real platform testing confirmed the instrument can meet the measurement requirements. The instrument is high-precision, energy-economical, mass-storage and user-friendly. Its able to work underwater continuously for up to one year. In addition, the small size minimizes the interference caused by the carriers motion. Compared with its foreign counterparts, the new instrument is inexpensive, so its suitable for extensive multi-point measurement. Now it has been installed in LH11-1 platform in the South China Sea for measurement of anchor chain inclination. Its the first time to employ measuring device with autonomous right in offshore platform monitoring in China.
The blade vibration analysis hypothesizing the blade a cantilever beam fixed on one end was presented, The vibration equation of HAWT(horizontal axis wind turbine) blade was developed by the finite element method. The analysis of natural vibration characteristics of an actual wind turbine model 7FD-200 was made by using the ALGOR-FEAS. In order to make the software appropriate to wind turbine blade, a net-generation module was developed with the BORLANDC3.1 language under the environment of AUTOCAD 12 for Win ADS (AutoCAD Development System). The blade finite element net can be generated automatically. In the calculation, the vibration of the blade is divided into three kinds of vibrations, including flap, flutter and torsion, The five lower order natural vibration frequencies and vibration shapes of each kind of vibration were calculated respectively.
Selected results of a study concerning the load bearing capacity and the seismic behavior of a prototype steel tower for a 450 kW wind turbine with a horizontal power transmission axle are presented. The main load bearing structure of the steel tower rises to almost 38 m high and consists of thin-wall cylindrical and conical parts, of varying diameters and wall thicknesses, which are linked together by bolted circular rings. The behavior and the load capacity of the structure have been studied with the aid of a refined finite element and other simplified models recommended by appropriate building codes. The structure is analyzed for static and seismic loads representing the effects of gravity, the operational and survival aerodynamic conditions, and possible site-dependent seismic motions. Comparative studies have been performed on the results of the above analyses and some useful conclusions are drawn pertaining to the effectiveness and accuracy of the various models used in this work.
This paper focuses on mitigation of dynamic loading induced on off-shore towers by drifting ice. Conical structures attached to off-shore towers at water level are widely used to reduce static and dynamic ice actions. The level of remaining forces is enough to cause severe tower vibrations, therefore a need for an additional device to reduce the remaining actions is recognized. Present study introduces a new, compliant connection between the cone and the tower. Parameters of the connection are controlled semi-actively to optimize the effect. Numerical studies are made to roughly estimate the effectiveness of the new solution. First, contact problem of ice sheet and cone is simulated using simplified material model for ice. Then a numerical model of a wind turbine tower is constructed. Dynamic interaction between cone and tower is simulated and the new solution effectiveness is discussed.
Structural vibration analysis wind turbine blades using finite element method, Acta Energiae Saris Sinica Static, seismic and stability analyses of a prototype wind turbine steel tower
- N S Bao
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- Z Q N Ye
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- H Karamaneas
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- D E Beskos
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Research on Structure Design of Wind Turbine Supporting System, thesis of master
- L Yan
Semi-Submersible Platform and Anchor Foundation Systems for Wind Turbine Support
- G R Fulto
- D J Malcolm
- H Elwany
- W Stewart
- E Moroz
- H Dempster
- G. R. Fulto