06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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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 Terrestrial laser scanning - a supplementary approach for 3D documentation and animation(2005) Böhm, JanWhile aerial methods undesputedly form the backbone of modern photogrammetry, we have seen an increased use of terrestrial methods in the past years to supplement aerial data especially in the field of 3D city modelling and the animation thereof. This article describes an approach to use terrestrial laser scanning in order to increase detail and realism of datasets derived from arial methods. When devising a new strategy for the integration of data from multiple sources two aspects come to focus. For one methods for the registration of the datasets are needed. Secondly a suitable data model has to be introduced to hold multiple aspects of the data. Consequently we present our methods for the automatted georeferencing of terrestrial laser data and we introduce the concept of LASERMAPs, which are extracted from terrestrial laser data and mapped onto the 3D building model.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 Automation in laser scanning for cultural heritage applications(2005) Böhm, Jan; Haala, Norbert; Alshawabkeh, YahyaWithin the paper we present the current activities of the Institute for Photogrammetry in cultural heritage documentation in Jordan. In particular two sites, Petra and Jerash, were recorded using terrestrial laser scanning (TLS). We present the results and the current status of the recording. Experiences drawn from these projects have led us to investigate more automated approaches to TLS data processing. We detail two approaches within this work. The automation of georeferencing for TLS data is presented along with our approach for automated feature extraction.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 Down-regulation and individual blade control as lifetime extension enablers(2018) Pettas, Vasilis; Cheng, Po WenAs more and more wind turbines are coming close to the end of their design lifetime, evaluation of end of life strategies is becoming highly relevant. Moreover, as turbine technology matures and wind farms grow larger, lifetime extension becomes a financially attractive option compared to re-powering and decommissioning. Present work suggests control strategies, namely down-regulation and individual blade control, as lifetime extension enablers. The concept of using them as retrofit control implementations is explained. Their individual and combined potential in fatigue load reduction is evaluated, along with their effect on other performance and pitch system metrics. Finally, the possible period of extension, beyond the nominal 20 years, is evaluated in an example case where the retrofit control strategy is applied after 15 years of baseline operation. The aeroelastic simulations are performed with a 10 MW reference wind turbine, according to load certification standards. Results show that the two methods complement each other in load alleviation. The pitch actuator demands are also significantly decreased when the two methods are combined.