Generated Wind Fields Research Articles

Impact of low-frequency fluctuations on loads of a fixed-bottom offshore reference wind turbine

Marine atmospheric turbulence is predominantly characterized by large-scale structures associated with low-frequency wind turbulence. However, conventional turbulence models for assessing wind turbine loads often fall short of adequately integrating these low-frequency wind fluctuations. In this study, we used a model for low-frequency wind fluctuations to generate wind fields representative of offshore wind conditions in the North Sea. The IEA 15 MW reference wind turbine was subjected to three distinct incoming wind fields: high-frequency (3D) turbulence, low-frequency (2D) turbulence combined with high-frequency (3D) turbulence, and 3D turbulence scaled by target or measured standard deviation of wind components. We found that increased damage equivalent loads by incorporating the low-frequency wind fields are only significant for the tower base fore-aft and blade root fore-aft moments. The impact of low-frequency wind turbulence on the damage equivalent loads was more pronounced for below-rated wind speeds. The scaled 3D turbulence yielded the highest lifetime damage equivalent loads, i.e., in the range of 8-18% more than the unscaled 3D turbulence and combined 2D +3D turbulence. This method leads to an overestimation of loads and, hence, more expensive turbines. Incorporating 2D+3D turbulence in wind fields resulted in a 3.8% increase in lifetime damage equivalent loads for the tower base fore-aft and blade root flapwise moments compared to unscaled 3D turbulence. These findings underscore the importance of considering low-frequency wind fluctuations in the turbine design process, especially for a more accurate estimation of loads.

Development and performance evaluation of a novel wind generation system for the floating wind turbine model test

The Wind Generation System (WGS) is an essential piece of equipment for the model test of the Floating Wind Turbine (FWT) in integrated wind & wave environment. With the evolution of FWT techniques, the requirements for the comprehensive performance of WGS are improved. In this paper, we develop a novel WGS with modular design philosophy, aiming to improve the temporal & spatial quality and controllability of the generated wind fields. 68 individually-controlled carbon fiber propellers are deployed in a hexagonal configuration to form a 4.2 m × 4.2 m wind generation area. Steady/dynamic and uniform/non-uniform wind fields can be reproduced, with the wind speed varying from 0 to 12 m/s. Extensive tests are conducted to assess the feasibility and performance of the proposed WGS. The statistical characteristics of the generated wind fields coincide well with the targets, demonstrating a satisfying comprehensive performance of the present WGS. Finally, the WGS is applied to evaluate a novel FWT concept in an integrated model test in wave basin. The FWT dynamic performances agree well with the expected ones from numerical simulation, further demonstrating that the proposed WGS could contribute to improving the accuracy and reliability of FWT model tests.

Structur Structural Dynamics of A al Dynamics of AWT-27 Wind T -27 Wind Turbine Blade urbine Blade

Wind energy is one of the world’s current leading renewable energy resources. One of the major aspects of studying wind turbines is the structural dynamics for the turbine structure including blades and support structure. In the current work, the blades of the Advanced Wind Turbine (AWT-27) are investigated in a dynamic approach. Different wind fields have been generated for the study to provide different Design Load Conditions (DLCs). Three laminar wind velocities of 5 m/s, 12 m/s, and 17 m/s were simulated. Turbulent wind flow fields have also been generated at the three standard classes A, B and C of high, medium, and low turbulence intensities respectively. The generated wind fields were used as inputs to calculate the aerodynamic loads for each wind condition using the Blade Element Momentum (BEM) theory. Aerodynamic loads have been calculated, namely, the shear force on five different locations along the blade length. Results of the simulation are summarized such that the shear forces at the blade root, 30%, 50%, 70% of the blade length are known for each wind condition. The summary serves as a guide for further optimization of the blade structural design.

Assessment of Wind Field Generation Methods on Predicted Wind Turbine Power Production Using a Free Vortex Filament Wake Approach

Abstract The generated power and thrust of a wind turbine strongly depend on the flow field around the turbine. In the present study, three different inflow methods, i.e., a time series (TS) from large eddy simulation (LES) of atmospheric boundary layer flow field, a synthetic turbulent flow field using the Mann model (MM), and a steady-state mean wind profile with shear, are integrated with the free vortex filament wake method to investigate the effect of wind field generation methods on the wind turbine performance where the impact of the turbine and the trailing wake vortices on the turbulent flow fields is ignored. For this purpose, an in-house vortex lattice free wake (VLFW) code is developed and used to predict the aerodynamic loads on rotor blades. The NREL 5-MW reference wind turbine is used for the VLFW simulations. For a fair assessment of different inflow generation methods on power production of a wind turbine, it is not sufficient that the generated wind fields employed in the TS and MM methods have the same streamwise mean velocity and turbulence intensity at hub height. Instead, the generated inflows must have equivalent power-spectral densities especially at low frequencies since the rotor blades essentially respond to the large-scale fluctuations (macroscopic scales) rather than small-scale fluctuations (microscopic scales). A faster energy decay rate of LES inflow leads to a higher energy content in the TS method at low frequencies (associated with the macroscopic dynamics of the rotor blades). This extra kinetic energy results in a slightly higher mean power production while using the TS method although the inflow conditions at hub height/rotor plane are the same for both the TS and MM methods. Moreover, the impact of simulation time (the length of time integration) on the power production of a wind turbine (exposed to an unsteady inflow) must be taken into account. A short simulation time remarkably affects the mean wind speed over the rotor area for identical turbulent inflows. For Taylor’s hypothesis application using a single LES flow field, the results show a significant difference in the mean powers corresponding to the different realizations due to large turbulent fluctuations.

A comparative study on the running safety of trains subjected to crosswinds simulated with different wind models

This article presents a study on the train stability against crosswinds simulated with different wind models. The work focuses on the evaluation of derailment indexes, which are dependent on the wheel-rail contact forces obtained through dynamic analyses performed with a vehicle-structure interaction methodology. The results obtained using the normative European Committee for Standardization (CEN) Discrete Gust model are compared with those obtained with a turbulent wind model based on stochastically generated wind fields. The calculations are performed considering several heights above the terrain to simulate the behaviour of a train running over a bridge deck located at different elevations. The CEN Discrete Gust model proved to be inaccurate and increasingly conservative, in relation to the Turbulent Wind model, as the height above the ground increases, since the former is based on a fixed turbulence intensity corresponding to the ground level, while the latter considers the correct turbulence intensity dependent on the deck elevation. Based on these results, the present article describes an alternative discrete gust approach that takes into consideration the variable turbulence intensity and terrain category in order to improve its applicability in the evaluation of the train running safety on bridges with decks located at different heights.

Latticed mode: A new control strategy for wind field simulation in a multiple-fan wind tunnel.

On the basis of the actively controlled multiple-fan wind tunnel we designed, this paper proposes a latticed mode-based control strategy for the fan array. The so-called latticed mode is the overall topology of the working fans. In order to investigate the simulation ability of the latticed mode, several latticed modes are designed to analyze the temporal and spatial properties of generated wind fields. Airflow data under different latticed modes are measured using nine two-dimensional anemometers, and then, statistical indicators of wind speed and wind direction, as well as the spatial uniformity and complexity of generated wind fields, are calculated to analyze the characteristics of wind records. The results indicate that the distribution of active fans in the latticed mode has significant influence on the statistical properties and spatial evolutions of wind speed and direction. Besides, the latticed modes can regulate the spatial uniformity and complexity of the wind fields. The latticed modes with a high clustering degree of active fans can generate wind fields with low spatial uniformity and high complexity. In addition to the fan voltage and the rotation angle of swivel plates, the proposed latticed mode provides more possibilities for wind field simulation.

Understanding Hurricane Storm Surge Generation and Propagation Using a Forecasting Model, Forecast Advisories and Best Track in a Wind Model, and Observed Data—Case Study Hurricane Rita

Meteorological forcing is the primary driving force and primary source of errors for storm surge forecasting. The objective of this study was to learn how forecasted meteorological forcing influences storm surge generation and propagation during a hurricane so that storm surge models can be reliably used to forecast actual events. Hindcasts and forecasts of Hurricane Rita (2005) storm surge was used as a case study. Meteorological forcing or surface wind/pressure fields for Hurricane Rita were generated using both the Weather Research and Forecasting (WRF) full-scale forecasting model along with archived hurricane advisories ingested into a sophisticated parametric wind model, namely Generalized Asymmetric Holland Model (GAHM). These wind fields were used to forecast Rita storm surges. Observation based wind fields from the OceanWeather Inc. (OWI) Interactive Objective Kinematic Analysis (IOKA) model, and Best track wind data ingested into the GAHM model were used to generate wind fields for comparison purposes. These wind fields were all used to hindcast Rita storm surges with the ADvanced CIRCulation (ADCIRC) model coupled with the Simulating Waves Nearshore (SWAN) model in a tightly coupled storm surge-wave model referred to as ADCIRC+SWAN. The surge results were compared against a quality-controlled database of observed data to assess the performance of these wind fields on storm surge generation and propagation. The surge hindcast produced by the OWI wind field performed the best, although some high water mark (HWM) locations were overpredicted. Although somewhat underpredicted, the WRF wind fields forecasted wider surge extent and wetted most HWM locations. The hindcast using the Best track parameters in the GAHM and the forecast using forecast/advisories from the National Hurricane Center (NHC) in the GAHM produced strong and narrow wind fields causing localized high surges, which resulted in overprediction near landfall while many HWM locations away from wind bands remained dry.

Trajectory Modelling of Atmospheric Pollutants Associated with Aircraft Emissions for Air Quality Assessment

Aviation is suffering a large increase in recent years and as result there is a consequent increase in emissions of air pollutants. The highest exposure levels of air pollution in airports and near them are found in the Landing and Take-off (LTO) cycle responsible for negative impacts on air quality. The city of Rio de Janeiro, in the coastal region of the South East of Brazil, has two major airports; the International airport and one for domestic flights. Both are near the Guanabara Bay (GB), in Metropolitan Region of Rio de Janeiro (MRRJ). In this research, it was verified the pollutant trajectories emitted by these two airports using the Brazilian Regional Atmospheric Modelling System (BRAMS) to generate wind fields in the MRRJ. From the wind fields, 3D kinematic trajectories Lagrangian model was used to calculate the pollutant trajectories. Atmospheric instability indices were tested from the BRAMS simulations to verify the days with more stable atmospheric conditions in winter month. The Total Totals index (TT) was selected to be more appropriate for the purpose of this study. Obtained results showed that the cities of Rio de Janeiro and Duque de Caxias, in the western of the MRRJ, are critical points to be affected continually by pollutant transport due to the prevailing meteorological conditions, harming the air quality in the region. These models captured the influence of mesoscale and large-scale systems, showing the dependence of the trajectories of both systems related to the season and time of day. They are important tools in decision-making for the control of emissions, contributing to better management of urban air quality.

Turbulent Extreme Event Simulations for Lidar-Assisted Wind Turbine Control

This work presents a wind field generator which allows to shape wind fields in the time domain while maintaining the spectral properties. This is done by an iterative generation of wind fields and by minimizing the error between wind characteristics of the generated wind fields and desired values. The method leads towards realistic ultimate load calculations for lidar-assisted control. This is demonstrated by fitting a turbulent wind field to an Extreme Operating Gust. The wind field is then used to compare a baseline feedback controller alone against a combined feedback and feedforward controller using simulated lidar measurements. The comparison confirms that the lidar-assisted controller is still able to significantly reduce the ultimate loads on the tower base under this more realistic conditions.

High resolution modelling of snow transport in complex terrain using downscaled MM5 wind fields

Abstract. Snow transport is one of the most dominant processes influencing the snow cover accumulation and ablation in high mountain environments. Hence, the spatial and temporal variability of the snow cover is significantly modified with respective consequences on the total amount of water in the snow pack, on the temporal dynamics of the runoff and on the energy balance of the surface. For the present study we used the snow transport model SnowModel in combination with MM5 (Penn State University – National Center for Atmospheric Research MM5 model) generated wind fields. In a first step the MM5 wind fields were downscaled by using a semi-empirical approach which accounts for the elevation difference of model and real topography, and vegetation. The target resolution of 30 m corresponds to the resolution of the best available DEM and land cover map of the test site Berchtesgaden National Park. For the numerical modelling, data of six automatic meteorological stations were used, comprising the winter season (September–August) of 2003/04 and 2004/05. In addition we had automatic snow depth measurements and periodic manual measurements of snow courses available for the validation of the results. It could be shown that the model performance of SnowModel could be improved by using downscaled MM5 wind fields for the test site. Furthermore, it was shown that an estimation of snow transport from surrounding areas to glaciers becomes possible by using downscaled MM5 wind fields.

Using wind fields from a high‐resolution atmospheric model for simulating snow dynamics in mountainous terrain

AbstractWind‐induced snow transport has remarkable effects on the snow cover spatial variability and on the temporal dynamics of snowmelt runoff. For accurate snow cover modelling, valid atmospheric forcing fields are essential. Since it is impossible to generate appropriate wind fields by a simple spatial interpolation of station data, a new approach was developed: A modified version of the Penn State University‐National Centre for Atmospheric Research (MM5) model was used to generate wind fields with 200‐m resolution. Because of the high computational costs of MM5, it was not practicable to include the wind field generation as an operational part of the snow cover modelling. Therefore, an archive consisting of 220 wind fields was generated prior to the simulation of the snow transport processes. These fields represent the most relevant synoptic situations for wind‐induced snow transport occurring at our test site. The criteria to generate which wind field to use in a specific snow model time step are mean wind speed and direction at the 700 hPa level derived from German Weather Service/Deutscher Wetterdienst (DWD) Lokalmodell (LM) analysis data. The wind field library provided physically derived wind speed and direction fields that were used to drive a snow transport model (SnowTran‐3D) in a high Alpine area in the Berchtesgaden National Park, Germany. In complex Alpine terrain, the procedure provides an alternative to simple interpolation methods, yielding improved physical realism at reasonable computational expense. Copyright © 2008 John Wiley & Sons, Ltd.

Hindcasting of storm waves using neural networks

Cyclone generated waves play a significant role in the design of coastal and offshore structures. Instead of conventional numerical models, neural network approach is used in the present study to estimate the wave parameters from cyclone generated wind fields. Eleven cyclones, which crossed the southern east coast of India between 1962 and 1979, are considered for analysis in this paper. The parametric hurricane wave prediction model by Young (1988) [Young, I.R., 1988. Parametric hurricane wave prediction model. Journal of Waterways Port Coastal and Ocean Engineering 114(5), 637–652] is used for hindcasting the wave heights and periods. Estimation of wave heights and periods is carried out using back propagation neural network with three updated algorithms, namely Rprop, Quickprop and superSAB. In neural network, the estimation is carried out using (i) difference between central and peripheral pressure, radius of maximum wind and speed of forward motion of cyclone as input nodes and the wave heights and periods as output nodes and (ii) wind speed and fetch as input nodes and wave heights and periods as output nodes. The estimated values using neural networks match well with those estimated using Young's model and a high correlation is obtained namely (0.99).

Wind field simulation

An efficient algorithm to simulate turbulent, atmospheric or wind tunnel generated wind fields is devised. The method is based on a model of the spectral tensor for atmospheric surface-layer turbulence at high wind speeds and can simulate two- or three-dimensional fields of one, two or three components of the wind velocity fluctuations. The spectral tensor is compared with and adjusted to several spectral models commonly used in wind engineering. Compared to the Sandia method (see Veers, P. S., Three-dimensional wind simulation. Technical Report SAND88-0152, Sandia National Laboratories, 1988) the algorithm is more efficient, simpler to implement, and in some respects more physical. The simulation method is currently used for load calculations on wind turbines and bridges.

STORM RELATED OIL SPILL MOVEMENT ON THE BEAUFORT SEA SHELF1

ABSTRACT A storm model is developed and applied to the north Alaskan coast. The model is used to generate wind fields from various storms which have occurred during the past 20 years. The wind fields generated are used to study the wind drift trajectories of oil spills from five different sites along the north Alaskan coast. The probability of an oil slick impacting the shoreline from the five different sites is discussed for different storms. Environmental risk analysis is discussed for drilling sites at different distances from the shoreline.