Nordex (Germany)

Abstract. For modern wind turbines, the effects of inflow wind fluctuations on the loads are becoming increasingly critical. Using field measurements of a full-scale operating wind turbine and simulated loads calculated with reconstructed wind fields from wind measurements from the GROWIAN campaign, we identify particular load events that lead to high values of the so-called damage equivalent loads. Remarkably, the simulations do not reproduce such load occurrences when standard synthetic turbulent wind fields are used as inflow. These standard wind fields are typically parameterized by statistics at a single measurement location (e.g., mean wind speed and turbulence intensity). In this article, we introduce a new characteristic of a wind field: the virtual center of wind pressure. The new feature is calculated from averages of the thrust force acting on a defined area, i.e., the rotor area of the turbine. We correlate these characteristics to the unusual load events observed in the operational measured data. Furthermore, we demonstrate that the introduced concept is an efficient tool to characterize large-scale structures within wind fields. We propose using the virtual center of wind pressure in conjunction with the well-defined single-location properties to consolidate improved descriptions of atmospheric wind and more accurate wind fields for turbine simulations.

Abstract. A non-investigated feature of the atmospheric turbulent wind, named periods of constant wind speed, is introduced and investigated. We hypothesize that such periods of constant wind speed are related to characteristic wind field structures (e.g., ramps or jets), which when interacting with a wind turbine may induce particular dynamical responses. Therefore, this study focuses on the characterization of the constant wind speed periods in terms of their lengths, probability of occurrence, and extreme events. Atmospheric offshore wind data are analyzed. Our findings reveal that the statistics of long constant wind speed periods are an intrinsic feature of the atmospheric boundary layer and show the challenging power law behaviour of extreme events, which depends on the local conditions and the precise definition of wind speed thresholds. A comparison to wind time series generated with standard synthetic wind models and to time series from ideal stationary turbulence suggests that these structures are not characteristics of small-scale turbulence but seem to be consequences of larger-scale structures of the atmospheric boundary layer, and thus are a typical multi-scale effect. Given the conclusive results, we show that the Continuous Time Random Walk model, as a non-standard wind model, can be adapted to generate the statistics of those periods of constant wind speed measured from the atmospheric turbulent wind.

Abstract. The outlined analysis validates the dynamic wake meandering (DWM) model based on loads and power production measured at an onshore wind farm with small turbine distances. Special focus is given to the performance of a version of the DWM model that was previously recalibrated at the site. The recalibration is based on measurements from a turbine nacelle-mounted lidar system. The different versions of the DWM model are compared to the commonly used Frandsen wake-added turbulence model. The results of the recalibrated wake model agree very well with the measurements, whereas the Frandsen model overestimates the loads drastically for short turbine distances. Furthermore, lidar measurements of the wind speed deficit as well as the wake meandering are incorporated in the DWM model definition in order to decrease the uncertainties.

Modern lightning protection systems for wind turbine blades with conducting structural elements, e.g., carbon fiber reinforced polymer (CFRP) spar caps, contain equipotential bonding joints to prevent sparking during strikes. Significant current levels are experienced through the joints and the characterization of the electrical contact at the bonding regions is essential for reliable protection. Therefore, this article aims to characterize the contact resistivity of several equipotential bonding joints. The proposed methodology first measures the total resistance of the samples, and then the bulk resistance of the conductive elements is computed using the finite-element method. The latter is required to predict the spreading effects in CFRP components due to the strong anisotropic nature of such materials. After that, the contact resistance is calculated by subtracting the predicted bulk resistances from the measured total resistances. The developed procedure was applied to three typical equipotential bonding materials: expanded copper foil (ECF), biaxial (BIAX) CFRP, and unidirectional (UD) CFRP. Both ECF and BIAX CFRP showed superior contact quality than the UD CFRP, with one to two orders of magnitude smaller contact resistivity.

Abstract. Light detection and ranging (lidar) systems have gained a great importance in today's wake characteristic measurements. The aim of this measurement campaign is to track the wake meandering and in a further step to validate the wind speed deficit in the meandering frame of reference (MFR) and in the fixed frame of reference using nacelle-mounted lidar measurements. Additionally, a comparison of the measured and the modeled wake degradation in the MFR was conducted. The simulations were done with two different versions of the dynamic wake meandering (DWM) model. These versions differ only in the description of the quasi-steady wake deficit. Based on the findings from the lidar measurements, the impact of the ambient turbulence intensity on the eddy viscosity definition in the quasi-steady deficit has been investigated and, subsequently, an improved correlation function has been determined, resulting in very good conformity between the new model and the measurements.

One of the key factors for automation systems in the domains smart grids, digital factories and modern process systems are the permanently shift of their requirements. Thus, software has to be evolve over time. This issue has been addressed by different solutions for evolving automation software. Though, they have their specific benefits, but lacks on deficiencies like a specific (non-standard) programming model, specific programming languages and a very narrow focus of a specific automation domain. In contrast to this a novel approach will be discussed to provide a more flexible and quite general solution, a common middleware, to reconfigure automation software dynamically with minimal downtime. A middleware to integrate different programming languages, container systems, frameworks, libraries, control applications and drivers as well.