Analysis Of Wind Turbine Towers Research Articles

Finite Element Formulation of Timoshenko Non Prismatic Beam Column Element for Static and Dynamic Analysis of Wind Turbine Towers

Finite Element Formulation of Timoshenko Non Prismatic Beam Column Element for Static and Dynamic Analysis of Wind Turbine Towers

Coupled Bending-Torsional Buckling Analysis of Wind Turbine Tower Including Warping Effect Using the Differential Quadrature Method

Coupled Bending-Torsional Buckling Analysis of Wind Turbine Tower Including Warping Effect Using the Differential Quadrature Method

Time and Frequency Domain Analysis of Wind Turbine Towers Under Spatially Correlated Wind Field

Time and Frequency Domain Analysis of Wind Turbine Towers Under Spatially Correlated Wind Field

A general frequency adaptive framework for damped response analysis of wind turbines

Dynamic response analysis of wind turbine towers plays a pivotal role in their analysis, design, stability, performance and safety. Despite extensive research, the quantification of general dynamic response remains challenging due to an inherent lack of the ability to model and incorporate damping from a physical standpoint. This paper develops a frequency adaptive framework for the analysis of the dynamic response of wind turbines under general harmonic forcing with a damped and flexible foundation. The proposed method is founded on an augmented dynamic stiffness formulation based on a Euler-Bernoulli beam-column with elastic end supports along with tip mass and rotary inertia arising from the nacelle of the wind turbine. The dynamic stiffness coefficients are derived from the complex-valued transcendental displacement function which is the exact solution of the governing partial differential equation with appropriate boundary conditions. The closed-form analytical expressions of the dynamic response derived in the paper are exact and valid for higher frequency ranges. The proposed approach avoids the classical modal analysis and consequently the ad-hoc use of the modal damping factors are not necessary. It is shown that the damping in the wind turbine dynamic analysis is completely captured by seven different physically-realistic damping factors. Numerical results shown in the paper quantify the distinctive nature of the impact of the different damping factors. The exact closed-form analytical expressions derived in the paper can be used for benchmarking related experimental and finite element studies and at the initial design/analysis stage.

Fatigue reliability analysis of wind turbine tower under random wind load

It is important to understand the vibration response and fatigue characteristics of the wind turbine structure. The fatigue reliability of the tower flange and bolt is studied in this paper. Firstly, by using the orthogonal expansion method and the Numerical-Theoretical method of random dynamic action, the random fluctuating wind field is expanded into a set of scattered points to calculate the wind load. The numerical calculation of the dynamic response of the wind turbine is verified with the measured data. Then, a fatigue probability calculation method based on the probability density evolution method is proposed. It is an effective method to substitute the fatigue damage D obtained by a rain flow counting method into the probability density evolution equation to solve the probability density of fatigue damage. In the end, a 1.5 MW wind turbine tower was taken as an example for analyzing the fatigue damage of its flange and bolt which considers the wind speed and wind direction distribution. By using the probability density evolution method, the evolution probability density curve clusters of the structural responses can be given accurately and quantitatively; thus, the reliability of the structure under random load can be conveniently obtained.

Seismic behavior analysis of wind turbine tower affected by hydrodynamic pressure based on a simplified calculation model

Abstract The interaction between water and structure will inevitably lead to the hydrodynamic pressure, which could change the dynamic behavior of the wind turbine tower under earthquake action. Based on the Morison hydrodynamic theory, a simplified calculation method of hydrodynamic pressure was proposed, and the effects of different water depths and hydrodynamic pressure on the seismic behavior of the wind turbine tower is investigated. The main results include: wind turbine tower in deep water is sensitive to water, and the deformation and energy dissipation capacity of the wind turbine tower are decreased affected by the hydrodynamic pressure; the influence of hydrodynamic pressure on the acceleration and displacement is related to the high frequency components of the seismic wave, and the effect of hydrodynamic pressure on the internal force, displacement, and acceleration increases with the increasing of the water depths under different earthquakes. Finally, a shaking table test is carried out, and the experimental results are in good agreement with the calculated results using our proposed method.

Collapse analysis of wind turbine tower under the coupled effects of wind and near‐field earthquake

AbstractIn this paper, the pattern of wind turbine tower collapse as a result of the coupled effects of wind and an intense, near‐field earthquake is investigated. The constitutive relation of the tower cylinder steel is simulated via a nonlinear kinematic hardening model, and the specific value of each parameter in the constitutive model is provided. A precise model of the tower structure coupled with the blade is created using a nonlinear, finite element method. This method is compared with the results from a static pushover test of a small cylindrical tower to validate the finite element modeling method in this research. Two earthquake wave sets are selected as inputs. One contains 20 near‐field velocity pulse‐like ground motion waves with various pulse periods; the other contains 20 ordinary far‐field ground motion waves. A wind turbine tower with a hub height of 60 m is selected as an example for analysis. The dynamic response of this tower as a result of the coupled effects of the two ground motion wave sets and a transient wind load is calculated using nonlinear time‐history analysis. The calculation results shows that the average horizontal displacement of the tower top as a result of the near‐field velocity pulse‐like ground motion is 33% larger than the case with far‐field ground motion. Finally, the seismic collapse vulnerability curve of this wind turbine tower is calculated. The seismic collapse capacity of the tower is evaluated, and the seismic collapse pattern of the tower is analyzed.

Output-only modal analysis of wind turbine tower based on vibration response under emergency stop

The identification technique of output-only modal parameters is proposed for the large wind turbine tower under emergency stop. Compared with the response of regular operating conditions, the immediate tower structural response under emergency stop much more resembles a state of free vibration, which is more appropriate for the modal identification of the wind turbine tower. The vibration response is measured in the nacelle, which is easy to perform in the field modal test. The variational mode decomposition (VMD) is applied to decompose the vibration response into several band-limited intrinsic mode functions. The free responses of decomposed functions are extracted by applying the random decrement technique (RDT). Finally, the modal damping ratio and natural frequency are identified from each free modal response by using the Hilbert transform method. Simulations and a 1.5 MW wind turbine field modal test results verify the effectiveness of the proposed identification method. The main modal parameters of wind turbine, including weak modes, are effectively extracted by using output-only vibration responses under emergency stop. The modal parameter identification method is provided for the large wind turbine structure under the engineering condition.

Wind load response of offshore wind turbine towers with fixed monopile platform

Wind turbine towers are continuously subjected to wind force as their major dynamic load. Dynamic response of the wind turbine tower subjected to wind forces is usually estimated by numerical methods such as finite element method (FEM). In this paper, the analytical transfer matrix method (TMM) is used to determine wind load response of wind turbine. Therefore, various and general models including coupled springs (CS), distributed springs (DS) and apparent fixity length (AF) models are employed for modeling of wind turbine foundation and axial force is modeled as a variable force along the tower, as well. Wind force is divided into two parts containing thrust and distributed force. The transfer matrix is derived based on Euler-Bernoulli's beam differential equation. The global transfer matrix is obtained by applying boundary conditions of the tower and constructing the point matrix. Then, the factors affecting the tower dynamic response such as foundation models, axial induction factor, terrain factor, wind shear and gust condition are examined in several case studies. Finally, the TMM results are compared with the available results in the literature such as of the FEM which show good agreement. The comparisons can be concluded that the TMM can be used instead of the conventional numerical methods maintaining high accuracy for wind induced vibration analysis of wind turbine towers.

A study and analysis of wind turbine towers with rotor size at different heights

<div><p><em>The aim of this paper is to study and analyse the size of rotor of wind turbine at heights. The study analysis of relevant data at set of for different hub heights of 30 m, 40 m, 50 m, 78 m and 100 m is carried out to compute power coefficient and extractable power. An increase in hub height caused an increase in energy generation of 3.52% and 6.28% for 78 m to 100 m, and for 78 m to 100 m hub heights, respectively. The results analysis leads to the power attainment in respect of height of hub and rotor size at a particular location of a wind farm. The data analytic finding leads to cost effective design of wind turbine to render required energy at that location of wind turbine.</em></p></div>

Nonlinear Response of Wind Turbines Under Wind and Seismic Excitations With Soil–Structure Interaction

The objective of this paper is to present an efficient beam formulation based on the boundary element method (BEM), for the nonlinear dynamic analysis of wind turbine towers of variable cross section founded either on surface or on monopile foundation system. The whole structure may undergo moderately large displacements, taking into account the effect of soil–structure kinematic and inertia interaction. The tower is subjected to the combined action of arbitrarily distributed or concentrated transverse wind loading as well as to seismic excitation together with axial loading arising from the self-weight of the tower and the mechanical parts. The Blade element momentum theory is taken into consideration in order to produce the wind load time histories, while the site seismic response is obtained through one dimensional shear wave propagation analysis. The soil–surface foundation system is formulated as equivalent lateral and rotational springs, while the case of monopile system is treated as a prismatic beam on elastic foundation assigning the corresponding springs and dashpots along its length. An extensive case study is carried out on a wind turbine tower–foundation system employing the generated wind velocity time histories and recorded earthquake accelerograms, providing insight to several structural phenomena. The results of the proposed model are compared wherever possible with those obtained from a commercial finite elements software package, illustrating the validity and the efficiency of the developed method. From the obtained results, the strong influence of the nonlinear effects on the dynamic response of the wind turbine tower is verified.

Reliability Analysis of Wind Turbine Towers

To increase energy density in order to meet increasing electricity demands, increasingly large-scale designs for wind turbines have been developed. Wind turbine towers of larger sizes can generate more electricity, but such large sizes also create higher costs in terms of development and maintenance. The present research sets up a wind turbine tower model, wherein the loads of towers are calculated by their relation to wind speed. The finite element method is used to analyze the stress distribution of towers under these loads. Impacts from different loads are compared as well. The wind speed distribution is derived from data collected in Penghu, Taiwan using statistical methods. Fatigue analysis of towers is then conducted using fatigue loads and wind speed distribution, and the mean time to failure (MTTF) of towers is calculated with quantitative reliability theory. The results show that the main loads of towers are the wind force acting on the rotation area of wind turbine blades and the moment caused by non-uniform wind speed. After comparing this research finding with loads calculated by a wind turbine design software, it is concluded that it is a feasible and conservative method to analyze a wind turbine tower structure with the loads calculated by its relation to wind speed. In addition, it is shown that both the average and maximum hourly wind speeds in Penghu can be fitted into Weibull distribution. In conclusion, the fatigue analysis shows that the probability is greater than 99.8% for the tower model's failure time to be above 331,416 cycles, and it further shows that the tower model in this research possesses appropriate fatigue durability and is considered a safe tower design for Penghu.

Vibration Characteristics Analysis of Wind Turbine Towers under Foundation Conditions

Based on a kind of 1.5MW large-scale horizontal axis wind turbine tower, the mechanical modeling of a wind turbine tower-foundation is established, the static and dynamic analysis of the model is carried out by ANSYS software. The top displacement of the system is calculated by the static analysis to meet the design requirements in engineering. In dynamic analysis, each pile foundation is equivalent to a group of springs for the simulation of horizontal and vertical rigidity of the pile. The influence of top mass and foundation elasticity on wind turbine tower modes is analyzed, and calculated the natural frequency of the tower within a certain scope of rigidity in different directions about the piles foundation. The results show that the natural frequency of the wind turbine tower is influenced significantly by the mass on the tower top and foundation rigidity. The study provides a theoretical basis for optimal design of the wind turbine.

The Finite Element Analysis of the Large Horizontal Axis Wind Turbine Generator Tower

Building finite element model of wind turbine tower, analyzing Static and modal of tower with using finite element analysis software ANSYS .Getting stress distribution, maximum displacement, natural frequencies and modes of vibration by finite element modal analysis of wind turbine tower and analyzing natural frequencies of wind turbine tower to determine whether to cause the tower and the wind wheel drive resonance.

Dynamic Analysis and Evaluation of Wind Turbine Towers

This paper presents static and dynamic analysis of wind turbine towers which is supporting a 1.5MW wind turbine based on the theory of FEM. In static analysis, the modal frequencies of the towers are analyzed without wind load. In dynamic analysis, by the fluid-coupling theory, the dynamic effect of wind loads on the towers is calculated. It can be concluded that the main errors under the different load situations is caused by the impact of fluid structure coupling.

Influence of Simplified Models on Seismic Response Analysis of Wind Turbine Towers

Abstract. The dynamic response of wind turbine tower under earthquake is analyzed by aid of the ANSYS program in this paper. To investigate the effects of simplification calculation models of blades and engines on calculation results, a blades-tower integrated finite element (FE) model and a mass-tower finite element (FE) model are established respectively. Then model analysis is discussed and the time history analysis of the system under the input of mean value earthquake record is carried out. The results show that seismic responses of a wind turbine tower are remarkable and seismic action may be the dominant factor in the design of wind turbine towers that located at a seismically active zone. Torsion effect of a tower is evident as a result of the impact of mass eccentricity. Bottom stress at the direction perpendicular to seismic waves is much bigger than that along it. It is also found that the blades-tower integrated finite element model can reflect more accurately the dynamic responses of the tower in the whole process of the earthquake and the “time-lag” effect by comparison, and these provide reliable reference to design and further research of towers.

Example of the buckling resistance strength analysis of wind turbine tower with large aspect ratio opening under complex loads

Example of the buckling resistance strength analysis of wind turbine tower with large aspect ratio opening under complex loads

A peak factor for non-Gaussian response analysis of wind turbine tower

Equivalent static wind load evaluation formulas considering the dynamic effects based on peak factor were proposed to estimate the design wind load on the wind turbine tower in complex terrain. The non-linear part of wind pressure was considered to estimate the mean wind loads. The peak factor based on a non-Gaussian assumption was derived to estimate the non-linearity of wind load, especially in the high turbulence intensity. The formula of the peak factor is simplified to a function of the third order moment (skewness) considering the spatial correlation of wind velocity, the resonance response and the background response. The proposed methods showed favorable agreements with dynamic wind response analysis by FEM.

Seismic response analysis of wind turbine towers including soil-structure interaction

In this paper, a multibody model of wind turbine towers with the consideration of soil—structure interaction (SSI) is proposed to investigate their dynamic responses to seismic excitations in time domain. Using joint beam elements, the elastic tower is discretized into many rigid bodies coupled elastically by constraint joints and springs. The SSI is represented by a frequency-independent discrete parameter model approximately. The governing motion equations are derived by the application of Lagrange formalism including Lagrange multipliers. To investigate the effects of SSI and the dynamic behaviour of wind turbine towers under aerodynamic loading and earthquake loading, the tower of a large wind turbine is modelled and simulated with recorded seismic excitations.