Content area
Abstract
Atmospheric icing of overhead power lines creates many serious electrical and mechanical problems in the transmission network due to the high adherence of ice to substrates. To avoid major breakdowns in the power network during severe ice storms, the improvement in mechanical characteristics of the line components, as well as anti-icing and de-icing techniques should be taken into consideration. The successful development of those techniques, in turn, requires good knowledge of the adherence and bulk strength characteristics of atmospheric ice.
The main objective of this research, as a part of the general ice shedding problem, is to present a model for viscoplastic behaviour of porous atmospheric ice in the ductile region. The effects of cracking activities should be added to the model to predict the material behaviour in transition and brittle regions. This can be done by modifying the formulations of elastic, viscoelastic and plastic material parameters for cracking activities, as well as the yield envelopes in higher ranges of strain rates.
Finally, the major scientific contributions of this study can be categorized by considering the pre-defined objectives and by pursuing the described general methodology as: (a) classification of atmospheric ice structure on power lines on the basis of its grain shape (texture) and c-axis orientation (fabric); (b) presenting three computer codes in Maple Mathematical Program for determining the elastic moduli of various types of freshwater ice (granular, columnar S1, S2, S3); (c) presenting a poroelastic model for modifying the elastic moduli of porous atmospheric ice; (d) presenting a cap-model plasticity for various types of porous atmospheric ice; (e) presenting the new freshwater ice yield envelopes in ductile region, which has a better agreement with the available test data, and then generalizing them to take the porosity into consideration by means of an elliptical moving cap; and (f) developing a user-defined material subroutine (UMAT) for viscoplastic behaviour of atmospheric ice in ductile region including the poroelastic, viscoelastic, and cap-model plasticity. (Abstract shortened by UMI.)
