Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
39 results
Search Results
Item Open Access Optimization of floating offshore wind turbine platforms with a self-tuning controller(2017) Lemmer, Frank; Müller, Kolja; Yu, Wei; Schlipf, David; Cheng, Po WenThe dynamic response of floating offshore wind turbines is complex and requires numerous design iterations in order to converge at a cost-efficient hull shape with reduced responses to wind and waves. In this article, a framework is presented, which allows the optimization of design parameters with respect to user-defined criteria such as load reduction and material costs. The optimization uses a simplified nonlinear model of the floating wind turbine and a self-tuning model-based controller. The results are shown for a concrete three-column semi-submersible and a 10MW wind turbine, for which a reduction of the fluctuating wind and wave loads is possible through the optimization. However, this happens at increased material costs for the platform due to voluminous heave plates or increased column spacing.Item Open Access Acoustic and seismic emissions from wind turbines(2017) Calarco, Francesca; Cheng, Po Wen; Zieger, Toni; Ritter, JoachimWith regards to the interdisciplinary “TremAc” Project funded by the German Federal Ministry for Economic Affairs and Energy, this paper examines acoustic and seismic emissions generated by wind turbines with the aim of identifying a better understanding of their interaction. Measurement campaigns will be carried out in the field around a single wind turbine plant and results in terms of acoustic and seismic signals will be correlated and then evaluated in relation to environmental factors such as wind speed, wind direction and temperature as well as to data related to the wind turbines-specifications (e.g. rotation speed).Item Open Access Flatness-based feedforward control of wind turbines using Lidar(2014) Schlipf, David; Cheng, Po WenCurrent lidar technology is offering a promising opportunity to take a fresh look at wind turbine control. This work evaluates a flatness-based feedforward approach, that allows to calculate the control action based on trajectories of the rotor speed and tower motion using wind measurements. The trajectories are planned online considering actuator constrains to regulate the rotor speed and minimize tower movements. The feedforward signals of the collective pitch and generator torque update can be combined with conventional feedback controllers. This facilitates the application on commercial wind turbines. Simulations using a realistic lidar simulator and a full aero-elastic model show considerable reduction of tower and shaft loads.Item Open Access Realistic simulations of extreme load cases with lidar-based feedforward control(2017) Hagemann, Tim; Haizmann, Florian; Schlipf, David; Cheng, Po WenThis work presents the development of a simulation environment which allows to simulate realistic extreme events with lidar-based feedforward control. This environment includes turbulent wind fields including extreme events, wind evolution and wind field scanning with a nacelle-based lidar system. It is designed to simulate lidar-based controllers in a realistic environment. In addition, a controller extension is proposed to identify and mitigate extreme events in wind fields based on lidar measurements. The combination of this extreme event controller with the realistic simulation environment is a promising tool for load reductions in wind turbines.Item Open Access How far do we see? Analysis of the measurement range of long-range lidar data for wind power forecasting(2017) Würth, Ines; Brenner, Alex; Wigger, Maayen; Cheng, Po WenItem Open Access Tidal current turbine wake and park layout in transient environments(2014) Arnold, Matthias; Cheng, Po Wen; Daus, Philipp; Biskup, FrankDue to orbital velocities of the waves, the characteristics of tidal current turbines change over time. Therefore the induction factor and subsequent the wake is time dependent. Within the present research this time dependency is investigated by using Computational Fluid Dynamics (CFD) with Virtual Free Surface (VFS) and Actuator Disc (ACD) models. Based on this setup several different wave and current scenarios are simulated and analyzed with respect to the transient velocities in the turbine wake. Special respect is taken to the velocity undulations radiated by the changing apparent velocities in the rotor plane. These undulations move with the wake of the tidal current turbines and increase wave loads on 2nd row turbines in a park. This paper presents an efficient method for simulation of wave and park interactions and investigates dynamic turbine wakes under a large variety of parameters. Based on these simulations a suggestion for a tidal park design with respect to a balance of fatigue loads and power output is concluded.Item Open Access Coupled MBS-CFD simulation of the IDEOL floating offshore wind turbine foundation compared to wave tank model test data(2015) Beyer, Friedemann; Choisnet, Thomas; Kretschmer, Matthias; Cheng, Po WenA two MW floating offshore wind turbine is currently developed within the EU-FP7 project FLOATGEN. A wave tank test of the floater model at 1/32th scale has been performed in extreme wave conditions. In the present study numerical calculations of the floating foundation with regular waves using coupled MBS-CFD methods are compared to experimental data enabling a validation. Results of the wave elevation, floater motion and mooring line tension show a very good correlation. Flow phenomena like vortex shedding at the hull of the floater are shown. The presented methodology provides detailed knowledge allowing analysis of wave impact and resulting load assessment of floating offshore structures.Item Open Access Reducing the uncertainty of lidar measurements in complex terrain using a linear model approach(2018) Hofsäß, Martin; Clifton, Andrew; Cheng, Po WenIn complex terrain, ground-based lidar wind speed measurements sometimes show noticeable differences compared to measurements made with in-situ sensors mounted on meteorological masts. These differences are mostly caused by the inhomogeneities of the flow field and the applied reconstruction methods. This study investigates three different methods to optimize the reconstruction algorithm in order to improve the agreement between lidar measurements and data from sensors on meteorological masts. The methods include a typical velocity azimuth display (VAD) method, a leave-one-out cross-validation method, and a linear model which takes into account the gradients of the wind velocity components. In addition, further aspects such as the influence of the half opening angle of the scanning cone and the scan duration are considered. The measurements were carried out with two different lidar systems, that measured simultaneously. The reference was a 100 m high meteorological mast. The measurements took place in complex terrain characterized by a 150 m high escarpment. The results from the individual methods are quantitatively compared with the measurements of the cup anemometer mounted on the meteorological mast by means of the three parameters of a linear regression (slope, offset, R2) and the width of the 5th–95th quantile. The results show that expanding the half angle of the scanning cone from 20◦ to 55◦ reduces the offset by a factor of 14.9, but reducing the scan duration does not have an observable benefit. The linear method has the lowest uncertainty and the best agreement with the reference data (i.e., lowest offset and scatter) of all of the methods that were investigated.Item Open Access Application of a Monte Carlo procedure for probabilistic fatigue design of floating offshore wind turbines(2018) Müller, Kolja; Cheng, Po WenFatigue load assessment of floating offshore wind turbines poses new challenges on the feasibility of numerical procedures. Due to the increased sensitivity of the considered system with respect to the environmental conditions from wind and ocean, the application of common procedures used for fixed-bottom structures results in either inaccurate simulation results or hard-to-quantify conservatism in the system design. Monte Carlo-based sampling procedures provide a more realistic approach to deal with the large variation in the environmental conditions, although basic randomization has shown slow convergence. Specialized sampling methods allow efficient coverage of the complete design space, resulting in faster convergence and hence a reduced number of required simulations. In this study, a quasi-random sampling approach based on Sobol sequences is applied to select representative events for the determination of the lifetime damage. This is calculated applying Monte Carlo integration, using subsets of a resulting total of 16 200 coupled time-domain simulations performed with the simulation code FAST. The considered system is the Danmarks Tekniske Universitet (DTU) 10 MW reference turbine installed on the LIFES50+ OO-Star Wind Floater Semi 10 MW floating platform. Statistical properties of the considered environmental parameters (i.e., wind speed, wave height and wave period) are determined based on the measurement data from the Gulf of Maine, USA. Convergence analyses show that it is sufficient to perform around 200 simulations in order to reach less than 10 % uncertainty of lifetime fatigue damage-equivalent loading. Complementary in-depth investigation is performed, focusing on the load sensitivity and the impact of outliers (i.e., values far away from the mean). Recommendations for the implementation of the proposed methodology in the design process are also provided.Item Open Access Comparison of measured and simulated structural loads of an offshore wind turbine at Alpha Ventus(2016) Müller, Kolja; Reiber, Mario; Cheng, Po WenA comparison of fatigue and extreme loads from simulations with full-scale measurements collected over a period of ten months in the offshore test field, Alpha Ventus, is presented in this paper. There are two goals of this study: (1) to check if the measured range of fatigue and extreme loads can be captured correctly by simulations when the variations of relevant environmental parameters are taken into account; and (2) to investigate if measured extreme loads can be reproduced by simulations when ten-minute averages of the environmental parameters are used. The results show a good overall match of loads when the variation of environmental parameters is considered but an insufficient match when the events of maximum load occurrence are compared.