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Simulation numérique d'un écoulement bidimensionnel de glace polaire présentant une anisotropie induite évolutive.

Abstract : Observations of crystal orientations on deep ice-cores from Antactica and Greenland have shown that polar ice acquires a fabric, characteristic of the strain-history it has undergone. Since the viscoplastic behaviour of the ice single crystal is strongly anisotropic, the macroscopic anisotropic behaviour of polycrystalline ice depends on the preferred orientation of its grains. At the scale of the ice polycrystal, the ice fabric is described by a continuous orientation distribution function (ODF) and the mechanical behaviour is obtained by assuming a linear transversely isotropic behaviour of each grain and a uniform state of stresses in the polycrystal (static model). With these assumptions, we have developped analytical results for the behaviour of the polycrystal and its fabric evolution, which allows the description of the fabric with only three parameters. At the scale of the ice sheet, the velocity and fabric fields of the stationary flow are solved by using a coupled method: - for a given fabric field, the corresponding velocity field is computed by the finite element method, - for a given velocity field, the corresponding field of fabrics is obtained by calculating fabric evolution along the flow streamlines, this two steps process being iterated until convergence is achieved. We show the influence of both temperature field and grain behaviour on fabric developpement in the ice sheet. We apply our model to the flow line going from GRIP to GISP2
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Olivier Gagliardini. Simulation numérique d'un écoulement bidimensionnel de glace polaire présentant une anisotropie induite évolutive.. Glaciologie. Université Joseph-Fourier - Grenoble I, 1999. Français. ⟨tel-00701282⟩

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