06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7

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Publication Type: search.filters.UBSTyp.ZeitschriftenartikelAuthor: search.filters.author.Cheng, Po WenAuthor: search.filters.author.Schlipf, David

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Now showing 1 - 5 of 5
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    Lidar-based wake tracking for closed-loop wind farm control
    (2017) Raach, Steffen; Schlipf, David; Cheng, Po Wen
    This work presents two advancements towards closed-loop wake redirection of a wind turbine. First, a model-based wake-tracking approach is presented, which uses a nacelle-based lidar system facing downwind to obtain information about the wake. The method uses a reduced-order wake model to track the wake. The wake tracking is demonstrated with lidar measurement data from an offshore campaign and with simulated lidar data from a simulation with the Simulator fOr Wind Farm Applications (SOWFA). Second, a controller for closed-loop wake steering is presented. It uses the wake-tracking information to set the yaw actuator of the wind turbine to redirect the wake to a desired position. Altogether, the two approaches enable a closed-loop wake redirection.
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    Four-dimensional wind field generation for the aeroelastic simulation of wind turbines with lidars
    (2022) Chen, Yiyin; Guo, Feng; Schlipf, David; Cheng, Po Wen
    Lidar-assisted control of wind turbines requires a wind field generator capable of simulating wind evolution. Out of this need, we extend the Veers method for 3D wind field generation to 4D and propose a two-step Cholesky decomposition approach. Based on this, we develop a 4D wind field generator - evoTurb - coupled with TurbSim and Mann turbulence generator. We further investigate the impacts of the spatial discretization in 4D wind fields on lidar simulations to provide practical suggestions.
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    Multibody modeling for concept-level floating offshore wind turbine design
    (2020) Lemmer, Frank; Yu, Wei; Luhmann, Birger; Schlipf, David; Cheng, Po Wen
    Existing Floating Offshore Wind Turbine (FOWT) platforms are usually designed using static or rigid-body models for the concept stage and, subsequently, sophisticated integrated aero-hydro-servo-elastic models, applicable for design certification. For the new technology of FOWTs, a comprehensive understanding of the system dynamics at the concept phase is crucial to save costs in later design phases. This requires low- and medium-fidelity models. The proposed modeling approach aims at representing no more than the relevant physical effects for the system dynamics. It consists, in its core, of a flexible multibody system. The applied Newton-Euler algorithm is independent of the multibody layout and avoids constraint equations. From the nonlinear model a linearized counterpart is derived. First, to be used for controller design and second, for an efficient calculation of the response to stochastic load spectra in the frequency-domain. From these spectra the fatigue damage is calculated with Dirlik’s method and short-term extremes by assuming a normal distribution of the response. The set of degrees of freedom is reduced, with a response calculated only in the two-dimensional plane, in which the aligned wind and wave forces act. The aerodynamic model is a quasistatic actuator disk model. The hydrodynamic model includes a simplified radiation model, based on potential flow-derived added mass coefficients and nodal viscous drag coefficients with an approximate representation of the second-order slow-drift forces. The verification through a comparison of the nonlinear and the linearized model against a higher-fidelity model and experiments shows that even with the simplifications, the system response magnitude at the system eigenfrequencies and the forced response magnitude to wind and wave forces can be well predicted. One-hour simulations complete in about 25 seconds and even less in the case of the frequency-domain model. Hence, large sensitivity studies and even multidisciplinary optimizations for systems engineering approaches are possible.
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    Adaptive Vorsteuerung für Windenergieanlagen
    (2013) Schlipf, David; Cheng, Po Wen
    Der Beitrag beschreibt, wie Windmessungen mit LIDAR in einer Vorsteuerung verwendet werden können, um die Drehzahlschwankungen und damit die Belastungen von Windenergieanlagen zu reduzieren. Kernstück dieser Vorsteuerung ist ein Filter, der adaptiv auf die aktuellen Messungen eingestellt werden muss, da sich die Prädiktionszeit und die Korrelation zwischen Vorhersage und Anlagenverhalten kontinuierlich ändern. Die Ergebnisse werden mit Messdaten einer 5MW Anlage validiert.
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    Control design methods for floating wind turbines for optimal disturbance rejection
    (2016) Lemmer, Frank; Schlipf, David; Cheng, Po Wen
    An analysis of the floating wind turbine as a multi-input-multi-output system investigating the effect of the control inputs on the system outputs is shown. These effects are compared to the ones of the disturbances from wind and waves in order to give insights for the selection of the control layout. The frequencies with the largest impact on the outputs due to the limited effect of the controlled variables are identified. Finally, an optimal controller is designed as a benchmark and compared to a conventional~PI-controller using only the rotor speed as input. Here, the previously found system properties, especially the difficulties to damp responses to wave excitation, are confirmed and verified through a spectral analysis with realistic environmental conditions. This comparison also assesses the quality of the employed simplified linear simulation model compared to the nonlinear model and shows that such an efficient frequency-domain evaluation for control design is feasible.