ALBERT

Description: We apply a modified proper orthogonal decomposition (POD) to large eddy simulation data of a wind turbine wake in a turbulent atmospheric boundary layer. The turbine is modeled as an actuator disk. Our analysis mainly focuses on the pragmatic identification of spatial modes, which yields a low order description of the wake flow. This reduction to a few degrees of freedom is a crucial first step for the development of simplified dynamic wake models based on modal decompositions. It is shown that only a few modes are necessary to capture the basic dynamical aspects of quantities that are relevant to a turbine in the wake flow. Furthermore, we show that the importance of the individual modes depends on the relevant quantity chosen. Therefore, the optimal choice of modes for a possible model could in principle depend on the application of interest. We additionally present a possible interpretation of the extracted modes by relating them to the specific properties of the wake. For example, the first mode is related to the horizontal large-scale movement.

Description: We propose a procedure to estimate the fatigue loads on wind turbines, based on a recent framework used for reconstructing data series of stochastic properties measured at wind turbines. Through a standard fatigue analysis, we show that it is possible to accurately estimate fatigue loads in any wind turbine within one wind park, using only the load measurements at one single turbine and the set of wind speed measurements. Our framework consists of deriving a stochastic differential equation that describes the evolution of the torque at one wind turbine driven by the wind speed. The stochastic equation is derived directly from the measurements and is afterwards used for predicting the fatigue loads for neighboring turbines. Such a framework could be used to mitigate the financial efforts usually necessary for placing measurement devices in all wind turbines within one wind farm. Finally, we also discuss the limitations and possible improvements of the proposed procedure.

Description: Energies, Vol. 11, Pages 612: Stochastic Wake Modelling Based on POD Analysis Energies doi: 10.3390/en11030612 Authors: David Bastine Lukas Vollmer Matthias Wächter Joachim Peinke In this work, large eddy simulation data is analysed to investigate a new stochastic modeling approach for the wake of a wind turbine. The data is generated by the large eddy simulation (LES) model PALM combined with an actuator disk with rotation representing the turbine. After applying a proper orthogonal decomposition (POD), three different stochastic models for the weighting coefficients of the POD modes are deduced resulting in three different wake models. Their performance is investigated mainly on the basis of aeroelastic simulations of a wind turbine in the wake. Three different load cases and their statistical characteristics are compared for the original LES, truncated PODs and the stochastic wake models including different numbers of POD modes. It is shown that approximately six POD modes are enough to capture the load dynamics on large temporal scales. Modeling the weighting coefficients as independent stochastic processes leads to similar load characteristics as in the case of the truncated POD. To complete this simplified wake description, we show evidence that the small-scale dynamics can be captured by adding to our model a homogeneous turbulent field. In this way, we present a procedure to derive stochastic wake models from costly computational fluid dynamics (CFD) calculations or elaborated experimental investigations. These numerically efficient models provide the added value of possible long-term studies. Depending on the aspects of interest, different minimalized models may be obtained.

Description: Scientific software takes on an increasingly prominent role in research. In particular in the sciences software has become an indispensable element in the research process. The way we handle software has a significant influence on the quality of research results, their traceability and reproducibility. In order to strengthen the recognition of scientific results achieved by software and to improve its visibility, the scientific community is actively working on concepts and solutions enabling researchers to publish software, cite it and be credited for it. For software to be a valuable and citeable contribution to science, the publication of scientific software must meet the quality criteria of the scientific discourse. As with data publication, defined processes and persistent identifiers should be used to make the results of research reproducible. Also, the specific needs of research have to be addressed and joined with experience gained in the field of development of free and open source software. A common understanding of handling scientific software with defined processes must be developed jointly. These processes have to address questions regarding quality assurance, versioning and documentation, traceability, reproducibility and reusability. Furthermore, the archiving of source code and executables, the use of persistent identifiers, and metrics measuring productivity, impact, and recognition have to be addressed. Especially when looking at software in the context of scientific publications only insufficient solutions exist to date. Even though it is possible to mint DOIs to identify archived source code copies, quality ensured by reviews is not addressed properly. But deserving credit for a software publication requires measures assessing the value of the published software. Subjectspecific reviews paired with softwarespecific expertise would open up new possibilities leveraging interdisciplinarity and the interplay of complementary scientific fields such as geosciences and computer science. Thus software publications and properly arranged reviews would foster the exchange in order to establish best practices from computer science in geosciences and to enhance subjectspecific software successively after its original publication.