Analysis of Octagonal Pile Supporting Offshore Wind Turbines Under Wave Loads

2014 ◽  
Author(s):  
Serena Lim ◽  
Longbin Tao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Computational Cost ◽  
Offshore Wind ◽  
Computational Time ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Element Method

Offshore wind energy development has gained considerable momentum around the world as wind is stronger and steadier offshore compared to land. This has led to a significant increase in production in recent years, especially offshore wind turbine embedded in shallow waters, such as the recent large scale offshore wind farms in the Northern Europe region. Being at the offshore waters, the wind turbines are subjected to harsh environment. The pile supporting the wind turbine must be reliable and able to withstand such sea condition. It is an important part of the design to study the structural behaviour of the piles under the wave loads. Due to the significant capital cost associated with the fabrication of the large circular cylinders, a new recommended innovative design to overcome such problem is to substitute the circular cylinder with a vertical monopile of octagonal cross-sectional shape. This paper describes the development of an efficient numerical model for structural analysis of wave interaction with octagonal pile using a modified semi analytical Scaled Boundary Finite Element Method (SBFEM). In contrast to the existing solutions obtained using the traditional methods such as the Finite Element Method (FEM) which typically suffer from high computational cost and the Boundary Element Method (BEM) which faces limitation from fundamental equations and problems with singularities. The most prominent advantage that SBFEM has over the FEM is in terms of the number of elements used for calculation and hence a reduction in computational time. When compared with BEM, the SBFEM does not suffer from computational stability problems.

Wave Diffraction Forces on Offshore Wind Turbine Piles With an Octagonal Cross Section

2013 ◽  
Author(s):  
Serena Lim ◽  
Longbin Tao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wave Diffraction ◽  
Offshore Wind ◽  
Circular Cylinders ◽  
Computational Time ◽  
Offshore Wind Turbine ◽  
Computational Stability ◽  
Irregular Frequency ◽  
Element Method

Traditional offshore wind turbines are normally supported by circular monopiles which are fabricated by rolling thick plates and welding them longitudinally. Due to the significant capital cost associated with the fabrication of such large circular cylinders, a new recommended innovative design to overcome such problem is introduced by replacing the circular cylinder with a vertical pile of octagonal cross-sectional shape. An efficient and very accurate semi-analytical/numerical solution based on the Scaled Boundary Finite Element Method (SBFEM) is developed to calculate the wave diffraction forces acting on the octagonal cylinders where no fundamental solutions known exist. Compared to the traditional Boundary Element Method (BEM), the SBFEM is free from the irregular frequency difficulty which means that it does not suffer from computational stability problems at sharp corners. The SBFEM solution also exhibits an enormous reduction of elements used to calculate the wave diffraction compared to the Finite Element Method (FEM), hence, a significant reduction in computational time. The SBFEM computation of the diffraction force demonstrates highly accurate results with a small number of surface elements. The presented method shows significant advantages, and is suitable for engineering applications especially the wave-structure interaction in the practical design.

scholarly journals Impacts of Mooring-Lines Hysteresis on Dynamic Response of Spar Floating Wind Turbine

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2109
Author(s):  
Weimin Chen ◽  
Shuangxi Guo ◽  
Yilun Li ◽  
Yijun Shen
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Wave Loads ◽  
Mooring Lines ◽  
Hysteresis Behavior ◽  
Floating Wind Turbine ◽  
Motion Responses ◽  
Element Method

Floating wind turbines often experience larger-amplitude motions caused by wind and ocean wave loads, while mooring-lines, such as catenary and taut mooring-lines, make the structure configurations along with an analysis of the global response more complicated compared to a fixed support foundation. Moreover, the restoring performance of dynamic mooring-lines exhibits a significant hysteresis behavior, and this hysteresis behavior may have profound impacts on the structural response of floating wind turbines under environmental loads. In this study, using the coupled finite element method, a dynamic simulation model is developed to study the motion responses of a spar floating wind turbine under consideration of mooring-lines hysteresis. In order to consider large-amplitude motion and nonlinear behaviors of catenary mooring-lines, a FEM (finite element method) model is developed based on a combination of 3D nonlinear beam elements and the super-element approach, and the interaction between mooring-lines and seabed is also included. Using our FEM numerical simulations, firstly, the restoring performance of mooring-lines and its hysteresis behavior are studied. Then, the motion responses, e.g., the displacements of the spar float undergoing various wave loads, are examined. The numerical results show that: the restoring stiffness of mooring-lines exhibits significant hysteresis behavior, and the restoring force is directionally dependent. Due to the hysteresis of restoring performance, for a case of regular wave conditions, little change of the spar surge in a steady-state is seen; however, for a case of extreme wave loads, the motion response gets about 14.4% smaller, compared with the quasi-static cases.

scholarly journals Support condition monitoring of offshore wind turbines using model updating techniques

2019 ◽  
Vol 19 (4) ◽  
pp. 1017-1031 ◽  
Author(s):  
Ying Xu ◽  
George Nikitas ◽  
Tong Zhang ◽  
Qinghua Han ◽  
Marios Chryssanthopoulos ◽  
...  
Keyword(s):  
Finite Element ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Model Updating ◽  
Element Model ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Support Condition ◽  
Offshore Wind Turbines ◽  
Wind Turbine System

The offshore wind turbines are dynamically sensitive, whose fundamental frequency can be very close to the forcing frequencies activated by the environmental and turbine loads. Minor changes of support conditions may lead to the shift of natural frequencies, and this could be disastrous if resonance happens. To monitor the support conditions and thus to enhance the safety of offshore wind turbines, a model updating method is developed in this study. A hybrid sensing system was fabricated and set up in the laboratory to investigate the long-term dynamic behaviour of the offshore wind turbine system with monopile foundation in sandy deposits. A finite element model was constructed to simulate structural behaviours of the offshore wind turbine system. Distributed nonlinear springs and a roller boundary condition are used to model the soil–structure interaction properties. The finite element model and the test results were used to analyse the variation of the support condition of the monopile, through an finite element model updating process using estimation of distribution algorithms. The results show that the fundamental frequency of the test model increases after a period under cyclic loading, which is attributed to the compaction of the surrounding sand instead of local damage of the structure. The hybrid sensing system is reliable to detect both the acceleration and strain responses of the offshore wind turbine model and can be potentially applied to the remote monitoring of real offshore wind turbines. The estimation of distribution algorithm–based model updating technique is demonstrated to be successful for the support condition monitoring of the offshore wind turbine system, which is potentially useful for other model updating and condition monitoring applications.

scholarly journals The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

2020 ◽  
Vol 8 (11) ◽  
pp. 859
Author(s):  
Thanh-Dam Pham ◽  
Hyunkyoung Shin
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Second Order ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Hydrodynamic Loads ◽  
Drift Motion ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU.

Study of Grouted Connections in Offshore Monopile Structures

2019 ◽  
Author(s):  
Efstathios E. Theotokoglou ◽  
Georgia Papaefthimiou
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stress State ◽  
Wind Turbine ◽  
Static Loading ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
The Finite Element Method ◽  
Analysis Problem ◽  
Mesh Density

Abstract In this paper the grouted connection (GC) of an offshore wind turbine is studied. The study is performed numerically by the finite element method (FEM). Initially, a description of the connection, its geometrical variations and its materials are presented. Moreover, analytical types about the deformation of the connection are presented. Subsequently, the analysis of the three dimensioned problem is performed numerically and the procedure as well as the parameters used, are given step by step. The case of the contact analysis problem is also studied. Practical issues such as mesh density and materials interaction are confronted. Finally, the stress state (SS) will be given in the analysis results, in order to specify the behavior of the connection under static loading.

Design and Structural Analysis of Mono Pile Foundation for Offshore Wind Turbines

2010 ◽  
Author(s):  
Jianhua Zhang ◽  
Zhenqing Wang ◽  
Liang Zhang ◽  
Ke Sun ◽  
Jun Hao
Keyword(s):  
Finite Element ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Pile Foundation ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Bohai Bay ◽  
Time Dynamic ◽  
Stress And Deformation

Offshore wind energy offers a huge potential for expansion of renewable energy in the world. However, placement of wind turbines in harsh offshore environments is an engineering challenge, which requires development of suitable foundation designs. This paper shows different foundation types which are decided by different cases of the seabed. The mono pile foundation for 1.5MW offshore wind turbine is designed for Bohai Bay in China considering the soil and seabed condition. A three dimensional (3D) finite element model of mono pile is established to analyze horizontal ultimate bearing capacity, stress and deformation under lateral loads. Through the modal analysis, the natural frequencies of the mono-pile are given. Results show that the designed mono pile can effectively preclude resonance with the wind turbine. Dynamic responses under wave and seismic loads are analyzed by transient analysis method. And at same time, dynamic amplification factors of stress and deformation are studied. The paper reaches the conclusion that the dynamic effect must be attached importance in the design. Moreover, based on the theory of stability, the simplified method to assess the ultimate buckling moment of the mono pile is put forward. Comparisons are also made with results calculated by codified rules of DNV and ABS and Finite Element Method. Besides, fatigue analysis is carried out according the codified rules of API. The numerical results demonstrate that the design of mono pile is reasonable and reliable. The research results can provide the reference for practical engineering in China.

scholarly journals Low-Computational-Cost Technique for Modeling Macro Fiber Composite Piezoelectric Actuators Using Finite Element Method

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4316
Author(s):  
Diaa Emad ◽  
Mohamed A. Fanni ◽  
Abdelfatah M. Mohamed ◽  
Shigeo Yoshida
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Fiber Composite ◽  
Computational Cost ◽  
Computational Time ◽  
Detailed Model ◽  
Computational Costs ◽  
Macro Fiber Composite ◽  
Low Computational Cost ◽  
Element Method

The large number of interdigitated electrodes (IDEs) in a macro fiber composite (MFC) piezoelectric actuator dictates using a very fine finite element (FE) mesh that requires extremely large computational costs, especially with a large number of actuators. The situation becomes infeasible if repeated finite element simulations are required, as in control tasks. In this paper, an efficient technique is proposed for modeling MFC using a finite element method. The proposed technique replaces the MFC actuator with an equivalent simple monolithic piezoceramic actuator using two electrodes only, which dramatically reduces the computational costs. The proposed technique was proven theoretically since it generates the same electric field, strain, and displacement as the physical MFC. Then, it was validated with the detailed FE model using the actual number of IDEs, as well as with experimental tests using triaxial rosette strain gauges. The computational costs for the simplified model compared with the detailed model were dramatically reduced by about 74% for memory usage, 99% for result file size, and 98.6% for computational time. Furthermore, the experimental results successfully verified the proposed technique with good consistency. To show the effectiveness of the proposed technique, it was used to simulate a morphing wing covered almost entirely by MFCs with low computational cost.

Static and Dynamic Characteristic Analysis of the Tower for Vertical Axis Wind Turbine Based on Finite Element Method

2012 ◽  
Vol 229-231 ◽  
pp. 613-616
Author(s):  
Yan Jue Gong ◽  
Yuan Yuan Zhang ◽  
Fu Zhao ◽  
Hui Yu Xiang ◽  
Chun Ling Meng ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wind Turbine ◽  
Dynamic Characteristic ◽  
Optimization Design ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine ◽  
Characteristic Analysis ◽  
Support Structure ◽  
Element Method

As an important part of the vertical axis wind turbine, the support structure should have high strength and stiffness. This article adopts finite element method to model a kind of tower structure of the vertical axis wind turbine and carry out static and modal analysis. The static and dynamic characteristic results of tower in this paper provide reference for optimization design the support structure of wind turbine further.

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