OOF2: The Manual

Find the element edges (Segments) that need to be refined. These are specified by the targets parameter, whose value is a RefinementTarget object. Different kinds of RefinementTarget objects pick segments in different ways, for example, by choosing all edges of heterogeneous elements or the long edges of skinny elements. See RefinementTarget for the details.

The criterion parameter is used to exclude certain elements and segments from the marking process. Setting it to Unconditional means that all elements and segments are possible candidates for refinement.

Figure "Refining a Skeleton" (a) shows a Skeleton that needs to have its heterogeneous elements refined. Setting targets to CheckHomogeneity(threshold=1) marks the edges of all elements whose homogeneity is less than 100%, as shown in Figure "Refining a Skeleton" (b).

Sometimes the way in which the elements will be subdivided (determined by the degree parameter) requires extra segments to be marked. In these cases a second pass is made through the Skeleton, marking additional segments.

After the segments are marked, each element is replaced by a suitable collection of smaller elements, such that each marked segment of the old Skeleton turns into a set number of segments of the new Skeleton. Exactly how this is done depends on the setting of the degree parameter, which determines both how many new edges replace each old edge, and how the new elements are arranged within the old element. (For details, see the descriptions of RefinementDegree and RuleSet.) The rules sometimes allow more than one way of subdividing an element. In those cases, the total effective energy of the new elements is computed, and the configuration with the lowest energy is used. The parameter alpha determines the relative contributions of shape and homogeneity to the effective energy, as discussed in Section 2.4.2.2.

Figure "Refining a Skeleton" (c) shows the result of refining a mesh using degree=Bisection(rule_set='liberal') and alpha=1.