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- Helanow, Christian, 1981-, et al.
(författare)
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Galerkin Least-Squares Stabilization in Ice Sheet Modeling - Accuracy, Robustness, and Comparison to other Techniques
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the accuracy and robustness of one of the most common methods used in glaciology for the discretization of the p-Stokes equations: equal order finite elements with Galerkin Least-Squares (GLS) stabilization. Furthermore we compare the results to other stabilized methods. We find that the vertical velocity component is more sensitive to the choice of GLS stabilization parameter than horizontal velocity. Additionally, the accuracy of the vertical velocity component is especially important since errors in this component can cause ice surface instabilities and propagate into future ice volume predictions. If the element cell size is set to the minimum edge length and the stabilization parameter is allowed to vary non-linearly with viscosity, the GLS stabilization parameter found in literature is a good choice on simple domains. However, near ice margins the standard parameter choice may result in significant oscillations in the vertical component of the surface velocity. For these cases, other stabilization techniques, such as the interior penalty method, result in better accuracy and are less sensitive to the choice of the stabilization parameter. During this work we also discovered that the manufactured solutions often used to evaluate errors in glaciology are not reliable due to high artificial surface forces at singularities. We perform our numerical experiments in both FEniCS and Elmer/Ice.
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| 2. |
- Löfgren, André, 1992-, et al.
(författare)
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Increasing Numerical Stability of Mountain Valley Glacier Simulations : Implementation and Testing of Free-Surface Stabilization in Elmer/Ice
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper concerns a numerical stabilization method for free-surface ice flow called the free-surface stabilizationalgorithm (FSSA). In the current study, the FSSA is implemented into the numerical ice-flow software Elmer/Ice and tested onsynthetic two-dimensional (2D) glaciers, as well as on the real-world glacier of Midtre Lovénbreen, Svalbard. For the synthetic2D cases it is found that the FSSA method increases the largest stable time-step size at least by a factor of ten for the case of agently sloping ice surface ( 3◦), and by at least a factor of five for cases of moderately to steeply inclined surfaces ( 6◦ − 12◦) .5Furthermore, the FSSA method increases the overall accuracy for all surface slopes. The largest stable time-step size is foundto be smallest for the case of a low sloping surface, despite having overall smaller velocities. For Midtre Lovénbreen the FSSAmethod doubles the largest stable time-step size, however, the accuracy is in this case slightly lowered in the deeper parts ofthe glacier, while it increases near edges. The implication is that the non-FSSA method might be more accurate at predictingglacier thinning, while the FSSA method is more suitable for predicting future glacier extent. A possible application of the10larger time-step sizes allowed for by the FSSA is for spin-up simulations, where relatively fast changing climate data can beincorporated on short time scales, while the slowly changing velocity field is updated over larger time scales.
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