scholarly journals Wind turbine load dynamics in the context of turbulence intermittency

2019 ◽  
Vol 4 (4) ◽  
pp. 581-594 ◽  
Author(s):  
Carl Michael Schwarz ◽  
Sebastian Ehrich ◽  
Joachim Peinke
Keyword(s):  
Wind Turbine ◽  
Design Guidelines ◽  
Elastic Model ◽  
Spatial Correlations ◽  
Wind Fields ◽  
Wind Structure ◽  
Turbulence Intermittency ◽  
Velocity Increments ◽  
Fatigue Loads ◽  
Non Gaussian

Abstract. The importance of a high-order statistical feature of wind, which is neglected in common wind models, is investigated: non-Gaussian distributed wind velocity increments related to the intermittency of turbulence and their impact on wind turbine dynamics and fatigue loads are the focus. Gaussian and non-Gaussian synthetic wind fields obtained from a continuous-time random walk model are compared and fed to a common aero-servo-elastic model of a wind turbine employing blade element momentum (BEM) aerodynamics. It is discussed why and how the effect of the non-Gaussian increment statistics has to be isolated. This is achieved by assuring that both types feature equivalent probability density functions, spectral properties and coherence, which makes them indistinguishable based on wind characterizations of common design guidelines. Due to limitations in the wind field genesis, idealized spatial correlations are considered. Three examples with idealized; differently sized wind structures are presented. A comparison between the resulting wind turbine loads is made. For the largest wind structure sizes, differences in the fatigue loads between intermittent and Gaussian are observed. These are potentially relevant in a wind turbine certification context. Subsequently, the dependency of this intermittency effect on the field's spatial variation is discussed. Towards very small structured fields, the effect vanishes.

scholarly journals Wind turbine load dynamics in the context of turbulence intermittency

2019 ◽  
Author(s):  
Carl Michael Schwarz ◽  
Sebastian Ehrich ◽  
Joachim Peinke
Keyword(s):  
Wind Turbine ◽  
Design Guidelines ◽  
Spatial Correlations ◽  
Wind Fields ◽  
Wind Structure ◽  
Turbulence Intermittency ◽  
Velocity Increments ◽  
Fatigue Loads ◽  
Non Gaussian ◽  
Blade Element

Abstract. The importance of a high order statistical feature of wind, which is neglected in common wind models, is investigated: Non-Gaussian distributed wind velocity increments related to the intermittency of turbulence and their impact on wind turbines dynamics and fatigue loads are in the focus. Two types of synthetic wind fields obtained from a Continuous-Time-Random Walk model are compared and fed to a common Blade-Element/Momentum theory based aero-servo-elastic wind turbine model. It is discussed why and how the effect of the non-Gaussian increment statistics has to be isolated. This is achieved by assuring that both types feature equivalent probability density functions, spectral properties and coherence, which makes them indistinguishable based on wind characterizations of common design guidelines. Due to limitations in the wind field genesis idealized spatial correlations are considered. Three examples with idealized, differently sized wind structures are presented. A comparison between the resulting wind turbine loads is made. For the largest wind structure sizes differences in the fatigue loads between intermittent and Gaussian are observed. These are potentially relevant in a wind turbine certification context. Subsequently, the dependency of this intermittency effect on the field's spatial variation is discussed. Towards very small structured fields the effect vanishes.

scholarly journals Applying a Random Time Mapping to Mann modelled turbulence for the generation of intermittent wind fields

2021 ◽  
Author(s):  
Khaled Yassin ◽  
Arne Helms ◽  
Daniela Moreno ◽  
Hassan Kassem ◽  
Leo Höning ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wind Field ◽  
Extreme Values ◽  
Random Time ◽  
Spatial Correlations ◽  
Wind Fields ◽  
Mapping Procedure ◽  
Velocity Increment ◽  
Non Gaussian ◽  
New Time

Abstract. A new approach to derive a synthetic wind field model which combines spatial correlations from the Mann model and intermittency is introduced. The term intermittency describes the transition from Gaussian to non-Gaussian velocity increment statistics at small scales, where non-Gaussian velocity increment statistics imply a higher probability for extreme values than a Gaussian distribution. The presented new model is named the Time-mapped Mann model. The intermittency is introduced by applying a special random time-mapping procedure to the regular Mann model. The Time-mapping procedure is based on the so-called Continuous-time random walk model. As will be shown, the new Time-mapped Mann field reflects spatial correlations from the Mann model in the plane perpendicular to flow direction and temporal intermittency. In a first wind turbine study, the new Time-mapped Mann field and a regular Mann field are used as inflow to a wind turbine in a Blade Element Momentum simulation. It is shown that the wind field intermittency carries over to the loads of the wind turbine, and, thus, shows the importance of carefully modeling synthetic wind fields.

scholarly journals Comparison of the Blade Element Momentum Theory with Computational Fluid Dynamics for Wind Turbine Simulations in Turbulent Inflow

2018 ◽  
Vol 8 (12) ◽  
pp. 2513 ◽  
Author(s):  
Sebastian Ehrich ◽  
Carl Schwarz ◽  
Hamid Rahimi ◽  
Bernhard Stoevesandt ◽  
Joachim Peinke
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Standard Deviation ◽  
Wind Turbine ◽  
Cfd Simulation ◽  
Wind Fields ◽  
Turbulent Inflow ◽  
Power Spectral ◽  
Fatigue Loads ◽  
Blade Element

In this work three different numerical methods are used to simulate a multi-megawatt class class wind turbine under turbulent inflow conditions. These methods are a blade resolved Computational Fluid Dynamics (CFD) simulation, an actuator line based CFD simulation and a Blade Element Momentum (BEM) approach with wind fields extracted from an empty CFD domain. For all three methods sectional and integral forces are investigated in terms of mean, standard deviation, power spectral density and fatigue loads. It is shown that the average axial and tangential forces are very similar in the mid span, but differ a lot near the root and tip, which is connected with smaller values for thrust and torque. The standard deviations in the sectional forces due to the turbulent wind fields are much higher almost everywhere for BEM than for the other two methods which leads to higher standard deviations in integral forces. The difference in the power spectral densities of sectional forces of all three methods depends highly on the radial position. However, the integral densities are in good agreement in the low frequency range for all methods. It is shown that the differences in the standard deviation between BEM and the CFD methods mainly stem from this part of the spectrum. Strong deviations are observed from 1.5 Hz onward. The fatigue loads of torque for the CFD based methods differ by only 0.4%, but BEM leads to a difference of up to 16%. For the thrust the BEM simulation results deviate by even 29% and the actuator line by 7% from the blade resolved case. An indication for a linear relation between standard deviation and fatigue loads for sectional as well as integral quantities is found.

Field monitoring of the ground vibrations adjacent to an onshore wind turbine foundation

2020 ◽  
Author(s):  
Pengpeng He ◽  
Jesús González-Hurtado ◽  
Tim Newson ◽  
Hanping Hong ◽  
Melanie Postman ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Near Field ◽  
Wind Farms ◽  
Field Monitoring ◽  
Vibration Monitoring ◽  
Onshore Wind ◽  
Wind Structure ◽  
Soil Foundation ◽  
Non Gaussian ◽  
Fluctuating Wind

Investigations of the soil-foundation interaction behavior of wind turbine foundations and transfer of energy from the wind to the ground have not been reported in Canada. Indeed, very few vibration monitoring studies have been conducted globally around wind farms. It has been found that turbines predominantly produce vibrations related to structural resonances and blade passing frequencies. Energy is found to be modified with distance and is dominated by surface waves. This paper describes a study of the effect of the wind-structure interaction on the behaviour of a turbine foundation and the generation of ground-based vibrations around a working commercial wind turbine in Ontario. The field monitoring system and meteorological instrumentation are described in this paper and the responses of the structure and the surrounding ground due to the fluctuating wind-field are discussed. The spectral analysis shows that the higher frequency vibrations attenuate more rapidly than the lower frequency vibrations. The tilted elliptical particle motions are found to be non-Gaussian because of the non-Gaussian wind conditions. The response attenuation with distance indicates that both geometric and material attenuation may dominate the vibration attenuation in the near field and only geometric attenuation occurs in the far field.

scholarly journals Fatigue Assessment of Monopile Supported Offshore Wind Turbine under Non-Gaussian Wind Field

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Bing Li ◽  
Kang Rong ◽  
Haifeng Cheng ◽  
Yongxin Wu
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Wind Turbines ◽  
Wind Field ◽  
Pile Foundation ◽  
Offshore Wind ◽  
Wind Fields ◽  
Offshore Wind Turbines ◽  
Non Gaussian

The vibration of offshore wind turbines caused by external loads is significant, which will cause fatigue damage to offshore wind turbines. Wind load is the main load during the operation period of the wind turbine, and available studies have shown that the external wind field often exhibits certain non-Gaussian characteristics. This article aims to obtain the fatigue assessment of the monopile foundation of the wind turbine under the non-Gaussian wind fields. A 5 MW wind turbine is selected in this article, and OpenFAST is applied to simulate the wind load. By comparing the Mises stress time histories of the pile foundation at a different depth, the fatigue analysis of the critical spots of the pile foundation is obtained. In the analysis of fatigue damage, the rain flow counting method is adopted, and the two-segment S-N curve is selected to analyze the fatigue life of the critical spots. The results show that, by taking the non-Gaussian characteristic of the wind field into account, the fatigue life of the monopile foundation decreases. Therefore, attention should be paid to the influence of non-Gaussian characteristics of wind fields on the fatigue life of monopile-supported wind turbines.

scholarly journals Holistic simulation of wind turbines with fully aero-elastic and electrical model

2021 ◽  
Author(s):  
Marcus Wiens ◽  
Sebastian Frahm ◽  
Philipp Thomas ◽  
Shoaib Kahn
Keyword(s):  
Renewable Energy ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Low Voltage ◽  
Renewable Energy Sources ◽  
Elastic Model ◽  
Electrical Model ◽  
Holistic Model ◽  
Electric System ◽  
Electrical Components

AbstractRequirements for the design of wind turbines advance facing the challenges of a high content of renewable energy sources in the public grid. A high percentage of renewable energy weaken the grid and grid faults become more likely, which add additional loads on the wind turbine. Load calculations with aero-elastic models are standard for the design of wind turbines. Components of the electric system are usually roughly modeled in aero-elastic models and therefore the effect of detailed electrical models on the load calculations is unclear. A holistic wind turbine model is obtained, by combining an aero-elastic model and detailed electrical model into one co-simulation. The holistic model, representing a DFIG turbine is compared to a standard aero-elastic model for load calculations. It is shown that a detailed modelling of the electrical components e.g., generator, converter, and grid, have an influence on the results of load calculations. An analysis of low-voltage-ride-trough events during turbulent wind shows massive increase of loads on the drive train and effects the tower loads. Furthermore, the presented holistic model could be used to investigate different control approaches on the wind turbine dynamics and loads. This approach is applicable to the modelling of a holistic wind park to investigate interaction on the electrical level and simultaneously evaluate the loads on the wind turbine.

scholarly journals Emergence of skewed non-Gaussian distributions of velocity increments in isotropic turbulence

2019 ◽  
Vol 4 (6) ◽  
Author(s):  
W. Sosa-Correa ◽  
R. M. Pereira ◽  
A. M. S. Macêdo ◽  
E. P. Raposo ◽  
D. S. P. Salazar ◽  
...  
Keyword(s):  
Isotropic Turbulence ◽  
Gaussian Distributions ◽  
Velocity Increments ◽  
Non Gaussian

Benchmark of a Novel Aero-Elastic Simulation Code for Small Scale VAWT Analysis

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
David Marten ◽  
Matthew Lennie ◽  
George Pechlivanoglou ◽  
Christian Oliver Paschereit ◽  
Alessandro Bianchini ◽  
...  
Keyword(s):  
Experimental Data ◽  
Wind Turbine ◽  
Open Source ◽  
Structural Model ◽  
Element Model ◽  
Small Scale ◽  
Elastic Model ◽  
Element Analysis ◽  
Simulation Code ◽  
Highly Nonlinear

After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90's in favor of horizontal axis wind turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfill this gap, a structural finite element analysis (FEA) model, based on the Open Source multiphysics library PROJECT::CHRONO, was recently integrated with the lifting line free vortex wake (LLFVW) method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34 m rotor. In this work, some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small-scale, fast-spinning (up to 450 rpm) VAWT. The study turbine is a helix shaped, 1 kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a one-dimensional beam element model and a more sophisticated shell element model. The resulting data represented an excellent basis for comparison and validation of the new aero-elastic coupling in QBlade. Based on the structural and aerodynamic data of the study turbine, an aero-elastic model was then constructed. A purely aerodynamic comparison to experimental data and a blade element momentum (BEM) simulation represented the benchmark for QBlade aerodynamic performance. Then, a purely structural analysis was carried out and compared to the numerical results from the former. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.

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