Wind

The RC propeller performance under steady and sinusoidally time-varying freestream (stream-wise or longitudinal gust) was investigated in the University of Dayton Low-Speed Wind Tunnel (UD-LSWT) in the open-jet configuration. The propellers were tested at varying incidence angles and reduced frequencies. The streamwise gust was created by actuating the shuttering system located at the test section exit and was characterized using hot-wire anemometry. A system identification model was developed for the shuttering system to determine the shutter actuation profile that would result in a sinusoidal gust in the test section. Changes in propeller thrust, power, and pitching moment were observed with an increase in propeller incidence angle under the steady freestream. The propeller’s steady freestream performance was then used to predict response under periodic streamwise gusts in edgewise flight. Below a reduced frequency of 0.2, the propeller response agrees with the prediction model, suggesting that the propeller response is quasi-steady. At reduced frequencies higher than 0.2, a reduction in mean thrust and pitching moment and significant phase lag was observed. Full article

With the growing expansion of renewable sources around the world, wind energy is among those that stand out. With the advances of technology, wind turbine projects have considerably increased their power, reaching higher power, mainly for offshore installations. One of the main challenges is the power converters, more specifically the semiconductor components, which have limited voltage and current capabilities. Thus, the concept of multilevel converters emerged, increasing the voltage levels and thus carrying higher power levels. In addition to the application of multilevel converters, it is possible to increase the voltage and power levels employing an open-end winding (OEW) connection to the generator. In this context, the present work investigated the application of a multilevel converter (three-level cascaded H-bridge back-to-back) driving a squirrel-cage induction machine in an open-end winding configuration, connected to a wind energy conversion system (WECS). The analysis of the proposed system was developed through dynamic simulation of a 1.67 MW WECS, using PLECS software, including the modeling of the main system components: generator, power converters, system control, filter, and grid connection. The results show that the objective of obtaining a 5-level behavior in the output voltage is achieved by using the OEW connection. Furthermore, a low harmonic content is achieved in the machine current as in the current injected into the grid. In addition, it is possible to verify the power distribution between the converters, demonstrating that converters with smaller power can be combined to reach higher WECS power. Full article

In this quick study, we estimated the Weibull distribution’s parameters using wind data collected between March 2017 and January 2018 using a twelve-meter mast meteorological station on the grounds of the National Energy Research Center in Khartoum. In order to quantify these descriptors, we relied on analytical and stochastic methods, subsequently enabling specialists from researchers, engineers, decision-makers, and policymakers to apprehend the wind characteristics in the vicinity. Hence, the computed scale and shape parameters were provided, in which the Firefly algorithm (FA) resulted in the most accuracy in terms of the coefficient of determination, which equaled 0.999, which we considered logical due to the observed nonlinearity in the wind speed numbers. On the contrary, the energy pattern factor method had the worst prediction capability depending on several goodness-of-fit metrics. This concise work is unique because it is the first to use data from Sudan to forecast local wind speeds using artificial intelligence algorithms, particularly the FA technique, which is widely used in solar photovoltaic modeling. Additionally, since classic estimating approaches act differently spatially, evaluating their efficacy becomes innovative, which was accomplished here. On a similar note, a weighted-average wind speed was found to equal $4.98 \mathrm{m}/\mathrm{s}$ and the FA average wind speed was $3.73 \mathrm{m}/\mathrm{s}$, while the rose diagram indicated that most winds with potential energy equivalent to $3 \mathrm{m}/\mathrm{s}$ or more blow from the north. Full article

As one of the preferred types of renewable energy, wind energy is rapidly growing. The purpose of this study is to provide a comprehensive and in-depth numerical analysis on the National Renewable Energy Lab (NREL) 5-MW offshore wind turbine to help understand the wind turbine’s aerodynamic features. In this research, the preprocessing was conducted by using SolidWorks modeling, and a realizable k-ε viscous model from ANSYS/FLUENT was used as the solver in the CFD simulation. Eight test cases were developed, and fixed inlet velocity 9 m/s was set as the baseline case. After the initial mesh independent study and model validation, a detailed numerical analysis was carried out. The results of near wake flow features, torque and thrust, pressure and pressure coefficient distribution, limiting streamline along wind turbine blades, power coefficient as a function of tip speed ratio were evaluated. Whenever possible, simulation results were compared with data in the literature (numerical or experimental), and good agreement was observed. The detailed wind turbine aerodynamic analysis results are expected to provide valuable input to wind turbine design and thus to improve the effectiveness of harnessing wind energy. Research is on the way to further understanding the influence of different inflow conditions on the aerodynamic characteristics. Full article

Most of the Brazilian territory is classified as a hot and humid climate, whose natural ventilation is one of the most important passive design strategies. The use of this strategy can be enhanced in the design through the shed roof air collectors or extractors. However, this strategy is not exploited by architecture design, due to the designers’ lack of knowledge about the efficiency of these devices. The article’s aim is to present guidelines for the design of shed roof air extractors and collectors, seeking to help designers to use these devices in buildings. The method is parametric studies, through CFD simulations. For the shed roof air extractors and collectors, the following is recommended: aerodynamic geometries; building with less depth and large air outlet openings. The increase in the number of sheds influences ventilation more than the change in the geometry of the sheds. For extraction, the area of the air outlet openings is the parameter that exerts the greatest influence on ventilation. For collection, the increase in the sizes of the openings of the sheds, without changing other parameters, does not significantly increase the air speed. Full article

Wave data play a critical role in offshore structure design and coastal vulnerability studies. For various reasons, such as equipment malfunctions, wave data are often incomplete. Despite the interest in completing the data, few studies have considered constructing a machine learning model with publicly available wind measurements as input, while wind data from reanalysis models are commonly used. In this work, ANNs are constructed and tested to fill in missing wave data and extend the original wave measurements in a basin with limited fetch where wind waves dominate. Input features for the ANN are obtained from the publicly available Integrated Surface Database (ISD) maintained by NOAA. The accuracy of the ANNs is also compared to a state-of-the-art reanalysis wave model, MEDSEA, maintained at Copernicus Marine Service. The results of this study show that ANNs can accurately fill in missing wave data and also extend beyond the measurement period, using the wind velocity magnitude and wind direction from nearby weather stations. The MEDSEA reanalysis data showed greater scatter compared to the reconstructed significant wave heights from ANN. Specifically, MEDSEA showed a 22% higher HH index for expanding wave data and a 33% higher HH index for filling in missing wave data points. Full article

As offshore wind capacity could grow substantially in the coming years, floating offshore wind turbines (FOWTs) are particularly expected to make a significant contribution to the anticipated global installed capacity. However, FOWTs are prone to several issues due partly to environmental perturbations and their system configuration which affect their performances and jeopardize their structural integrity. Therefore, advanced control mechanisms are required to ensure good performance and operation of FOWTs. In this study, a model predictive control (MPC) is proposed to regulate FOWTs’ power, reposition their platforms to reach predefined target positions and ensure their structural stability. An efficient nonlinear state space model is used as the internal MPC predictive model. The control strategy is based on the direct manipulation of the thrust force using three control inputs, namely the yaw angle, the collective blade pitch angle, and the generator torque without the necessity of additional actuators. The proposed controller accounts for the environmental perturbations and satisfies the system constraints to ensure good performance and operation of the FOWTs. A realistic scenario for a 5-MW reference wind turbine, modeled using OpenFAST and Simulink, has been provided to demonstrate the robustness of the proposed MPC controller. Furthermore, the comparison of the MPC model and a proportional-integral-derivative (PID) model to satisfy the three predefined objectives indicates the superior performances of the MPC controller. Full article

Wind energy holds a leading position among other renewable energy sources in electricity production. The competitive advantage of wind turbines to be connected to every electrical grid around the world and the 2030 targets of the EU have led to their high penetration in all countries, and especially European ones. Wind power plants are installed in areas with sufficient wind conditions, which simultaneously, are exposed to lightning activity, creating risks in their smooth operation. Considering the fact that there are more wind power installations in areas with different soil and topographic characteristics and the demand for the reliable, economically efficient, and smooth operation of the wind turbines, there is a need for standardized solutions that can be adapted to project-specific characteristics. In the current work it is introduced a methodology that intends to provide modular lightning protection for wind turbines and wind power plants, with the main drivers being the techno-commerciality and high availability of the facility, which can be adopted in most of the sites having as basis the relevant international standards. Full article

High-rise buildings cause accelerated winds around them. However, the interference effects of high-rise buildings on the surrounding low-rise buildings in urban blocks have not been evaluated. This study investigated the wind pressure coefficients on the roofs and walls of low-rise buildings surrounding a high-rise building through wind tunnel experiments. Seventy-two wind directions were considered from 0° to 355° in 5° increments, and the influence of the wind direction on the wind pressure coefficients of surrounding buildings was evaluated. At a 30° wind direction angle, the positive and negative peak wind pressure coefficients occurred in a low-rise building at the leeward side of the high-rise building. The positive peak pressure, approximately 1.4 times that without a nearby high-rise building, occurred at the windward corner on the front wall of a low-rise building. The negative peak value, approximately three times that without a nearby high-rise building, was observed at the windward edge on the roof of a low-rise building. Thus, accelerated winds caused by high-rise buildings may result in unexpected damage to the surrounding low-rise buildings. Full article

Given the 516 Arouca pedestrian suspension bridge’s design and characteristics, the owner, a municipality, required a set of tests in order to evaluate its aerodynamic characteristics and dynamic response, aiming at both structural safety and user comfort. Wind tunnel tests were performed over a sectional scaled model to obtain the static aerodynamic coefficients and dynamic response. The tests were carried out on different bridge configurations—a deck with people and a deck with an arch for secondary cables (connecting each suspension point to the catenary on the opposite side of the deck)—for the static coefficients. For the dynamic response, only the deck alone was tested. A major challenge had to be overcome, as the main displacement mode belonged to a swing movement, to assemble a wind tunnel setting, requiring a suspension system allowing wind displacements. A persistent trend of small amplitude displacements was identified, influencing user comfort and contributing to the installation of the secondary cables, but no aerodynamic instabilities were identified. Full article

High-rise buildings in cities adversely affect wind regimes by changing the air currents in their surrounding areas. In particular, extreme climate phenomena caused by climate change are stronger and more frequent, causing damage in cities. To better understand skyscraper wind behaviors around high-rise buildings, actual measurements are necessary to determine the environmental assessment of the wind effect. In this study, field measurements were performed with five anemometers at five points in the vicinity of a skyscraper called the LCT residential complex (411.6 m tall) surrounded by high-rise buildings in the coastal city of Busan, South Korea during Typhoon Hinnamnor. The gust was 3.7 times stronger, while the maximum 1-min mean wind speed was 3.1 times stronger than those measured at a nearby reference weather station operated by the Korean Meteorological Administration. The characteristics of downward and canyon winds were shown to depend on the spatiotemporal characteristics of the five points. The turbulence intensity declined as the wind speed increased and converged to a certain value. The gust factor also dropped as the wind speed increased and converged to 2.0, and was considered to be the parameter that best represents the intensity of instantaneous gust caused by the skyscraper wind effect. These results suggest that high-rise buildings should be designed with the consideration of gusts twice as strong as the average wind speed. In addition, field measurements should be accompanied in order to respond to the skyscraper wind effect. Full article

Wind loads for the design of wind-resistant high-rise buildings are generally evaluated based on spectral modal analysis or time-history response analysis using wind pressure data obtained from wind tunnel experiments with rigid models. The characteristics of the fluctuating wind pressures around vibrating buildings must be evaluated for relevant wind-resistant designs because the wind pressures around buildings are affected by their vibrations. One of the methods to investigate fluctuating fields is complex proper orthogonal decomposition (CPOD), which can express complicated pressure fields, including advection phenomena, as coherent structures. This paper presents the phase characteristics of fluctuating wind pressures around rigid and elastic models of a square-sectioned prism evaluated via CPOD analysis using the results of wind tunnel experiments. The evaluation procedure for the symmetricity of the fluctuating wind pressure modes obtained via CPOD is presented. The similarity of fluctuating wind pressure fields is evaluated as the congruency of the planes formed by the 1st- and 2nd-eigenmodes. With symmetricity and similarity, the fluctuating wind pressure fields are classified into three types: resonant and non-resonant states in smooth flow, and in gradient flow. The characteristics of the three types of wind pressure fields are shown, respectively, in the symmetric and anti-symmetric modes. Full article

This study investigated the impact of ice formation on the performance and aerodynamics of a vertical axis wind turbine (VAWT). This is an area that is becoming more prevalent as VAWTs are installed alongside horizontal axis wind turbines (HAWTs) in high altitude areas with cold and wet climates where ice is likely to form. Computational fluid dynamics (CFD) simulations were performed on a VAWT without icing in Ansys to understand its performance before introducing ice shapes obtained through the LewInt ice accretion software and repeating simulations in Ansys. These simulations were verified by performing a wind tunnel experiment on a scale VAWT model with and without 3D printed ice shapes attached to the blades. The clean blade simulations found that wind speed had little impact on the performance, while reducing the blade scale severely reduced performance. The ice formation simulations found that increasing the icing time or liquid water content (LWC) led to increased ice thickness. Additionally, glaze ice and rime ice conditions were investigated, and it was found that rime ice conditions that occur in lower temperatures caused more ice to form. The simulations with the attached ice shapes found a maximum reduction in performance of 40%, and the experiments found that the ice shapes made the VAWT unable to produce power. Full article

Since manual inspections of offshore wind turbines are costly, there is a need for remote monitoring of their health condition, including health prognostics. In this paper, we focus on corrosion detection and corrosion prognosis since corrosion is a major failure mode of offshore wind turbine structures. In particular, we propose an algorithm for corrosion detection and three algorithms for corrosion prognosis by using Bayesian filtering approaches, and quantitatively compare their accuracy against synthetic datasets having characteristics typical for wall thickness measurements using ultrasound sensors. We found that a corrosion prognosis algorithm based on the Pourbaix corrosion model using unscented Kalman filtering outperforms the algorithms based on a linear corrosion model and the bimodal corrosion model introduced by Melchers. Full article

Pitch systems form an essential part of today’s wind turbines; they are used for power regulation and serve as part of a turbine’s safety system. Hydraulic pitch systems include hydraulic accumulators, which comprise a crucial part of the safety system, as they are used to store energy for emergency shutdowns. However, accumulators may be subject to gas leakage, which is the primary failure mode. Gas leakage affects the performance of the accumulator and, in extreme cases, compromises the safety function of the pitch system. This paper deals with the development and experimental validation of an algorithm to detect gas leakage in piston-type accumulators. The innovation of the algorithm is the ability to generate estimates of the remaining amount of gas while solving the drift problem evidenced in previous research. Additionally, this method enables the ability to isolate gas leakage to a single accumulator out of a bank of accumulators. The approach is based on a State Augmented Extended Kalman Filter (SAEKF), which utilizes an extended thermal model of the accumulator, as well as temperature measurements along the accumulator surface to estimate the remaining gas in the accumulator. The method is experimentally validated and addresses the drift problem in estimating the gas leakage evidenced from previous research. Additionally, the method can identify and isolate gas leakage to a single accumulator from a bank of accumulators. Full article

Equivalent Static Wind Loads (ESWL) are desired in structural design to consider peak dynamic wind effects. Conventional ESWLs are for structures without control. For flexible structures with vibration control devices, the investigation of ESWL is required. Inerter-based Vibration Absorbers (IVAs), due to the light weight and high performance, gained much research attention recently. This paper established a generic analytical framework of ESWL for structures with IVAs. The analytical optimal design formulas for IVAs with different configurations and installation locations are provided. Subsequently, the solutions to uncontrolled and controlled wind-induced responses are derived based on the filter approach. Finally, the ESWL for controlled structures are presented with a gust response factor approach. The ESWL estimation for a tall chimney controlled by IVAs is illustrated, and the results revealed a significant ESWL reduction effect of the IVAs, particularly for the cross-wind vortex resonance. In the presented framework, the conventional uncontrolled ESWL can be converted to the controlled one with a control ratio. The closed form solution of the control ratio is provided, which enables a quick estimation of ESWL for controlled structures particularly in the preliminary design stage. The presented approach has the potential to be extended to more complex structures and vibration control devices. Full article

Corrosion is the leading cause of failure for Offshore Wind Turbine (OWT) structures and it is characterized by a low probability of detection. With focus on uniform corrosion, we propose a corrosion detection and prognosis system coupled with a Decision Support Tool (DST) and a Graphical User Interface (GUI). By considering wall thickness measurements at different critical points along the wind turbine tower, the proposed corrosion detection and prognosis system—based on Kalman filtering, empirical corrosion models and reliability theory—estimates the Remaining Useful Life of the structure with regard to uniform corrosion. The DST provides a systematic approach for evaluating the results of the prognosis module together with economical information, to assess the different possible actions and their optimal timing. Focus is placed on the optimization of the decommissioning time of OWTs. The case of decommissioning is relevant as corrosion—especially in the splash zone of the tower—makes maintenance difficult and very costly, and corrosion inevitably leads to the end of life of the OWT structure. The proposed algorithms are illustrated with examples. The custom GUI facilitates the interpretation of results of the prognosis module and the economical optimization, and the interaction with the user for setting the different parameters and costs involved. Full article

An accurate choice of the inflow parameters has been shown to affect the CFD results significantly. In this study, the actuator disk method (AD) is used to investigate the effects of the widely used inflow formulations, the logarithmic and power-law formulations, in the neutral atmospheric boundary layer simulations. Based on the one-dimensional momentum theory, the AD model is a rapid method that replaces the turbine with a permeable disk and is among the most used methods in the literature. The results of the k-$\omega$ AD simulation indicated that in spite of the logarithmic method’s widespread use, the power law formulation gives a better description of the velocity field. Furthermore, an actuator disk thickness study also showed that given the effect of actuator disk thickness on the rate of convergence, more attention should be dedicated towards finding a suitable disk thickness value. The combination of an optimized mesh and a suitable choice of AD thickness can help with the rate of convergence which in turn shortens the simulation’s run time. Full article