Site specific simulation of ice shed and ice throw from wind turbines using ballistic models (EISBALL)
Mai 2018 – March 2021
Contact: Markus Drapalik
Wind energy is to play an important role in Austria’s future energy mix. The expansion of wind energy is limited, among other things, by the fact that numerous favorable sites have already been used. The replacement of older turbines with more powerful ones (repowering) at favorable locations, which is already taking place, is also insufficient with regard to the political objective. Therefore, new areas need to be developed, making technically more challenging sites such as forests and (pre-)alpine areas interesting.
With increasing complexity of the terrain or greater icing frequency, the importance of risk analyses for ice fall or throw also increases. For this purpose, ballistic models are usually used to calculate the drop or throw distances. However, the models currently in use have significant weaknesses. The comparison between experiments and model calculations shows that none of the existing models can reproduce the fall distances satisfactorily. Furthermore, no reliability limits are known for the existing models, which means that much higher distances between wind turbines and infrastructures have to be chosen for safety reasons.
In this project, these problems were solved by the development of a new model and corresponding simulation tools. Observations and 1:1 experiments served as data basis. The latter have the decisive advantage of being able to produce large numbers of samples independent of weather conditions, thus enabling statistically significant statements to be made. During the experiments, test specimens were dropped or thrown from wind turbines. The specimens used were based on 3D scans of real ice fragments, which were collected and digitized in several observation campaigns. Using a 3D printing process, these were reproduced in suitable density and sufficient number. This achieves an unprecedented degree of realism.
The model itself is based on a model with six degrees of freedom (6DOF Model), for the complete representation of all possibilities of translation and rotation. In contrast to other models, the resulting moments are also taken into account here in addition to the acting forces. The corresponding values are pre-calculated by means of Computational Fluid Dynamics. They are available in tabular form for the simulation in order to minimize computation times. The resulting complex trajectories can be intersected with a terrain model to determine the impact point.
It can be shown, that in in comparison to established models, smaller drop distances but much wider distributions are found. This may allow for smaller safety distances. At the same time, however, the entire risk distribution in the vicinity of a wind turbine changes, whereby areas are possibly classified as being at risk that were not previously so. Of particular note is that the improved safety analyses and validated values for ice fall and ice throw potentially enable the development of new sites that currently cannot be developed or can only be developed to a limited extent due to overly conservative safety distances. Thus, there is the possibility to directly influence the wind energy expansion potential in Austria.
Monte Carlo simulation was performed for selected ice fragment types using the known parameters from experiments. The model results were compared with the experimental data. Here, the model input parameters were randomly varied depending on the reliability of their values, and thus 500 simulated drops per experimental drop were calculated. The qualitative comparison between experimental and simulated impact points shows a good representation of the spatial scatter.
The 90% confidence intervals of the respective values were chosen as a measure for the comparison of the simulation results and the experimental values. In the plot, the very good agreement between both ellipses can be seen.
|WEB Windenergie AG
|Energie Burgenland Windkraft
This project was funded under the Energy Research Program (4th call) of the Austrian Climate and Energy Fund in cooperation with the Austrian Research Promotion Agency (FFG).
The final report will be published here.
In order to enable transparency as well as an independent evaluation of the project results and to ensure the necessary safety for users of the derived safety considerations, the aggregated experimental data will be published here in a freely accessible way. In addition, the source code of both the newly developed model and other reference models will be published, allowing independent verification of the model. This is a significant advance over the safety analyses performed so far, whose data basis and model are not accessible and therefore not verifiable. When using the data, the author Markus Drapalik, Institute of Safety and Risk Sciences, University of Natural Resources and Applied Life Sciences, Vienna, should be cited, and the source code is published under the MIT license (attached to the code).
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