# Difference between revisions of "Solution of the Blatter-Pattyn model"

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− | This looks pretty scary eh? | + | This looks pretty scary eh? Yes, there is a lot of work to be done here. But, luckily, there is also a lot of symmetry here. Notice that if we wanted to design subroutines to discretize these equations, we could re-use a lot of them in multiple places by passing the appropriate arguments. For example, in many places, the only difference between the two equations is whether or not we are differentiating ''u'' or ''v'' (so apply the disrectization to either ''u'' or ''v'') and/or whether or not differentiation is with respect to ''x'' or ''y'' (so pass the argument, either ''x'', or ''y'', where appropriate). |

## Revision as of 22:30, 12 August 2009

The final form of the equations we'd like to solve is:

Again, note that for the *x* equation we've moved all the terms containing gradients in *v* to the right-hand side (RHS).

We've set it up this way in order to solve the equations using an **operator splitting** approach; for the *x* equation, we treat *v* as known (where we take the values of *v* from the previous iteration) and solve for *u*, and vice versa when we solve they *y* equation for *v*. The "splitting" refers to the fact that we are breaking the multi-dimensional divergence operation into multiple steps. Rather than solving one big matrix equation for *u* and *v* simultaneously we solve two smaller matrix equations in sequence with one of the unknowns treated as a known "source" term.

As with the 0-order model, we need to change from Cartesian to sigma coordinates. The first normal-stress term first term on the left-hand side becomes

where hatted values refer to the coordinate directions in sigma coordinates. Similarly, the first cross-stress term on the RHS is given by

This looks pretty scary eh? Yes, there is a lot of work to be done here. But, luckily, there is also a lot of symmetry here. Notice that if we wanted to design subroutines to discretize these equations, we could re-use a lot of them in multiple places by passing the appropriate arguments. For example, in many places, the only difference between the two equations is whether or not we are differentiating *u* or *v* (so apply the disrectization to either *u* or *v*) and/or whether or not differentiation is with respect to *x* or *y* (so pass the argument, either *x*, or *y*, where appropriate).