Investigating Coherent Structures in the Standard Turbulence Models using Proper Orthogonal Decomposition

Eliassen, Lene; Andersen, Søren Juhl

doi:10.1088/1742-6596/753/3/032040

Cited by 6 publications

(6 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The cumulative energy content in the first 100 POD modes (of 3072 nonzero modes in the present simulations) was obtained from the eigenvalues and is shown in Figure . Consistent with the findings in Eliassen and Andersen, the first mode contributed roughly 20% of the total energy for both models, while subsequent modes had smaller contributions. Beyond the first mode, the Mann model had more energy concentrated in lower modes compared with the Kaimal model, as shown in the right side of Figure .…”

Section: Resultssupporting

confidence: 93%

“…In the present study, the undisturbed turbulent flow field is of interest. The coherent structures in the generated wind field for wind turbines have also been investigated previously . Saranyasoontorn related the coherent structures found in the POD analysis to the structural response of a small land‐based wind turbine and found that only a few of the lowest POD modes were required to compute the low frequency energy in the wind turbine response .…”

Section: Introductionmentioning

confidence: 84%

“…Eliassen studied the differences in the spatial coherence between the Kaimal and Mann model using POD and showed that the two turbulence models differed in shape for the lowest POD modes. The Mann model had structures that were horizontally stretched relative to the Kaimal model …”

Section: Introductionmentioning

confidence: 99%

“…The coherent structures in the generated wind field for wind turbines have also been investigated previously. 18,19 Saranyasoontorn related the coherent structures found in the POD analysis to the structural response of a small land-based wind turbine and found that only a few of the lowest POD modes were required to compute the low frequency energy in the wind turbine response. 19 Eliassen studied the differences in the spatial coherence between the Kaimal and Mann model using POD and showed that the two turbulence models differed in shape for the lowest POD modes.…”

mentioning

confidence: 99%

“…The Mann model had structures that were horizontally stretched relative to the Kaimal model. 18 The present work examines differences in response of three representative 5 MW FWTs (semi-submersible, spar, and TLP) when applying the Mann and Kaimal turbulent wind fields. The differences in the results are discussed with respect to a POD of the wind fields, which provides an intuitive explanation for why the coherence modelling can have important consequences for the global responses.…”

mentioning

confidence: 99%

See 4 more Smart Citations

The effects of coherent structures on the global response of floating offshore wind turbines

Bachynski

Eliassen

2018

Wind Energy

Self Cite

View full text Add to dashboard Cite

The global dynamic response of floating wind turbines is commonly simulated using aero‐hydro‐servo‐elastic tools that consider numerically generated wind files as input. Based on the guidelines given in existing standards, two methods of generating such wind files are typically used: the Mann uniform shear model and the Kaimal spectral and exponential coherence model. Both models consider the Kaimal spectrum with similar frequency characteristics: The main difference between the approaches is related to the spatial coherence. The present work examines the consequences of using the two different wind file generation methods for estimating the global responses of representative spar, semi‐submersible, and tension leg platform (TLP) 5 MW wind turbines. Predictions of the standard deviation of low‐frequency responses in operational conditions, including motions at the natural frequency in surge and pitch as well as quasi‐static (spar, TLP) and resonant (semi‐submersible) motions in yaw, are seen to differ up to 30% to 40% depending on the wind field model. The differences in motion responses have important consequences for the design of the mooring system components. Proper orthogonal decomposition (POD) techniques are used to qualitatively explain the differing spatial coherence of the wind field. Simulations including a limited number of POD modes in the wind field highlight the importance of the low‐frequency, energy‐rich modes, suggesting that this type of visualization can be a useful tool.

show abstract

Section: Resultssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

The effects of coherent structures on the global response of floating offshore wind turbines

Bachynski

Eliassen

2018

Wind Energy

Self Cite

View full text Add to dashboard Cite

show abstract

Evaluation of different wind fields for the investigation of the dynamic response of offshore wind turbines

et al. 2020

View full text Add to dashboard Cite

As the size of offshore wind turbines increases, a realistic representation of the spatiotemporal distribution of the incident wind field becomes crucial for modeling the dynamic response of the turbine. The International Electrotechnical Commission (IEC) standard for wind turbine design recommends two turbulence models for simulations of the incident wind field, the Mann spectral tensor model, and the Kaimal spectral and exponential coherence model. In particular, for floating wind turbines, these standard models are challenged by more sophisticated ones. The characteristics of the wind field depend on the stability conditions of the atmosphere, which neither of the standard turbulence models account for. The spatial and temporal distribution of the turbulence, represented by coherence, is not modeled consistently by the two standard models. In this study, the Mann spectral tensor model and the Kaimal spectral and exponential coherence model are compared with wind fields constructed from offshore measurements and obtained from large‐eddy simulations. Cross sections and durations relevant for offshore wind turbine design are considered. Coherent structures from the different simulators are studied across various stability conditions and wind speeds through coherence and proper orthogonal decomposition mode plots. As expected, the standard models represent neutral stratification better than they do stable and unstable. Depending upon the method used for generating the wind field, significant differences in the spatial and temporal distribution of coherence are found. Consequently, the computed structural design loads on a wind turbine are expected to vary significantly depending upon the employed turbulence model. The knowledge gained in this study will be used in future studies to quantify the effect of various turbulence models on the dynamic response of large offshore wind turbines.

show abstract

A Model for Low-Frequency, Anisotropic Wind Fluctuations and Coherences in the Marine Atmosphere

Syed,

Mann

2024

Boundary-Layer Meteorol

View full text Add to dashboard Cite

To assess dynamic loads, large offshore wind turbines need detailed and reliable statistical information on the inflow turbulence. We present a model that includes low frequencies down to $$\sim 1$$ ∼ 1 hr$$^{-1}$$ - 1 using the observed $$S(f) \propto f^{-5/3}$$ S ( f ) ∝ f - 5 / 3 in that range. The presented model contains a parameter representing the anisotropy of the two-dimensional, incompressible turbulence, and it assumes the low-frequency fluctuations to be homogeneous in the vertical direction. Combined with a three-dimensional model for the smaller scales, the model can predict correlations between different points. We have validated the model against two offshore wind data sets: a nacelle-mounted, forward-looking Doppler lidar with four beams at the Hywind Scotland offshore wind farm and sonic anemometer measurements at the FINO1 research platform in the North Sea. One-point auto spectra and two-point cross spectra were calculated after splitting the data into different atmospheric stability classes. The relative strength of the 2D low-frequency fluctuations to the 3D fluctuations was higher under stable conditions. The combined 2D+3D model was able to fit the measured spectra with good accuracy and could then predict the two-point cross spectra, co-coherences, and phase angles between wind fluctuations at different lateral and vertical separations. Good agreement was found between the measured and predicted values, albeit with exceptions. The model can generate stochastic wind fields for investigating wake meandering in wind farms or dynamic loads on floating wind turbines.

show abstract

Investigating Coherent Structures in the Standard Turbulence Models using Proper Orthogonal Decomposition

Cited by 6 publications

References 4 publications

The effects of coherent structures on the global response of floating offshore wind turbines

The effects of coherent structures on the global response of floating offshore wind turbines

Evaluation of different wind fields for the investigation of the dynamic response of offshore wind turbines

A Model for Low-Frequency, Anisotropic Wind Fluctuations and Coherences in the Marine Atmosphere

Contact Info

Product

Resources

About