Material update procedure for planar transient flow of ice with evolving anisotropy
Abstract:A flow law for polar ice is derived, which takes into account the effect of deformation-induced anisotropy due to hexagonal single-crystal symmetry. Attention is focused on the main effect of crystal-lattice rotation. Existence of a continuous so-called orientation-distribution function, ODF, for the crystals is assumed. With its help the micro-scale constitutive behaviour is transformed to the large-scale. This transformation is simplified by imposing different consistency conditions (CC) due to Voigt–Taylor (VT) and Sachs–Reuss (SR), respectively. Here we take the grain interaction into account by linearly combining the VT and the SR conditions, i.e. by one additional parameter determining the relative weight of the two. A coupled finite-element–finite-volume approach is used to account for fabric evolution at the ice-sheet scale. For different CC, VT and SR, an orientation update is derived for planar flow, which results in only three additional degrees of freedom at each finite-element integration point to account for orthotropic material symmetry. Computations for the GRIP-core data demonstrate that a better fit can be obtained than with VT or SR alone.
Document Type: Research Article
Publication date: 2000-01-01
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