Experimental investigation of ice shed from wind turbines
Contact: Markus Drapalik
The investigations of the Institute for Safety and Risk Sciences (ISR) on the risk of ice shed were initially driven by the comparatively short-term need of the Austrian operators for assessments on this subject.
Due to the comparatively small number of icing events and the technical difficulties of observing them in nature, it could be assumed that a sufficient number of samples would not be obtainable in acceptable time. Thus, test specimens made of wood in various sizes and formats were used for drop experiments – the first of their kind. These were dropped from different heights and the resulting drop distances were recorded. Following the simplification that is used in most ballistic models, cuboidal specimens have been produced in various dimensions. The drop experiments were carried out either using helicopters or wind turbines.
While these early experiments provided useful insights into the challenges of the investigation of ice shed, it soon became apparent that the great simplification of the specimens could have a significant impact.
As a result, observations were made of naturally occurring ice shed, whereby the shape and size of falling pieces of ice, amounts of ice on rotor blades, and the trajectories and distribution of fragments on the ground were recorded (link: monitoring of ice shed). Based on these data, further advanced experiments with artificial specimens were carried out, as natural events occur too rarely to generate a statistically robust database.
In the context of these experiments, which are continued in the project Eisball (link) and extended to small wind turbines in the project Urban Wind Energy (link), a series of near-natural specimens were produced in addition to the existing, highly simplified test specimens. Additionally the specimen were generated in various detail increments to examine the influence of simplification on the outcome of the experiments.
So far, two drop experiments using 205 and 275 specimens have been performed with the support of Energie Burgenland Windkraft (http://www.energieburgenland.at/oekoenergie/windkraft/unternehmen/kurzportraet.html). Shed distances were recorded as well as the trajectories of the individual specimens. The database generated in this way is the only one in the world for the systematic, experimental research of ice fall and ice throw.
Publications of the results can be found here:
Drapalik, Markus: Experimental investigation of risk from ice throw and ice shed. Winterwind, FEB 6-8, 2017, Skellefteå, Sweden, http://winterwind.se/wp-content/uploads/2015/08/3_1_03_Drapalik_Experimental_investigation_of_risk_from_ice_throw_and_ice_shed_Pub_v1.pdf
Drapalik, M; Bredesen, R E: Experimental validation of models for ice shed risk analysis. World Wind Energy Conference, WWEC2017, , 12, JUN 12-14, 2017, Malmö, Sweden, https://wwec2017.com/wp-content/uploads/2017/06/Drapalik-Bredesen-Experimental-validation-of-models-for-ice-shed-risk-analysis.pdf
Drapalik, M.; Formayer, H.; Kromp, W. & Pospichal, B.; Budelmann, H.; Holst, A. & Proske, D. (Eds.): Risk of ice shed from wind turbines. Proceedings of the 9th International Probabilistic Workshop, 2011