| Résumé | A large suite of tests of the Blade Runners concept for reducing ice-induced vibration of structures was conducted in NRC/OCRE’s Large Cold Room facility using a set of differing ice crushing platens that had a variety of blade arrays on them. These Phase II tests were intended to investigate the factors that influence the performance of the technology and to identify the best performing Blade Runners crushing platens. In general two types of tests were conducted: (a) tests where crushing was from the vertical direction and where the platens were fixed from movement in the horizontal direction and (b) tests where the platens were moved horizontally during the crushing to investigate frictional aspects of the technology. For most cases high-speed imaging was used to observe the ice contact zone, by viewing through the platens that were made of acrylic, as it evolved during the tests. Blade shape, orientation and array spacing were investigated as well as platen material. Vertical crushing rates were in the range 10 – 30 mm/s and the horizontal sliding rates were in the range 4.14 – 30 mm/s. All tests were conducted at -10 oC. Three types of freshwater ice were used and 14 platens with open arrays of blades were tested. Results showed that blade shapes and array spacing was important factors and that square-column and square-pyramid blades performed well. The arithmetic average of the high- roughness profiles for the surfaces of the two best performing platens were 0.075 mm (square pyramids) and 0.375 mm (square columns). Load records from tests using flat bladeless crushing platens exhibited a high-amplitude sawtooth load pattern, resulting from fairly regular ice spalling events, that is typical of ice crushing in the brittle regime. This type of spalling behavior, and associated sawtooth load pattern, is responsible for ice-induced vibration of structures when ice sheets encroach on them. The high-performance Blade Runners platens significantly reduced the amplitude of the sawtooth load patterns. During tests there was no evidence of entrapment of crushed ice between blades nor was there any evidence of high frictional forces on the platens during tests involving horizontal sliding. |
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