POLYFLOW - Performances of UDF versus PMAT functions

POLYFLOW simulations involving UDF are usually computationally more expensive than without UDF. In order to reduce the required calculation time, UDF are evaluated only once per element by default, and are subsequently extrapolated to the other integration points in the current element, along with the formula
UDF(Z) = UDF(Z0)+(dUDF/dZ|Zo).(Z-Zo)
where Z is the variable used in the UDF, and Zo is the value of the variable at the first integration point. If the UDF is sensitive with respect to the variable Z, or if the variable Z significantly varies over one element, it is possible that the UDF be unproperly evaluated at the other points, in view of the extrapolation.
When necessary, the evaluation of UDF functions can be improved by using the keyword FULLEVALUDF in the .p3rc file or as a POLYFLOW option in POLYMAN. This requires additional calculation time, but shows the same quality as the PMAT functions. A remedy that we would suggest consists of trying to use the available functions in the PMAT menu, whenever possible. Of course, this may not allways be sufficient, although, in many circumstances, the use of polynomial expressions or of the Arrhenius exponential type may already provide viable approximations. Let us remind here that the functions available in the PMAT menu can be combined, under the form of sum, products, inverse sum or inverse products.

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