Error estimators and indicators

The type of error estimator is selected by eetype, and the [errorestimatorparams (…)] group in the same record then carries the parameters belonging to it.

Table 7 Supported error estimators and indicators.

Error estimator/indicator	eetype
EET_SEI	0
EET_ZZEE	1
EET_CZZSI	2

EET_SEI

A scalar error indicator. It indicates the element error from the value of some suitable scalar — damage level or plastic strain level, for example — obtained from the element integration points and the corresponding material model.

EET_ZZEE

The Zienkiewicz-Zhu error estimator. It requires special element algorithms, which may not be available for every element type.

EET_CZZSI

A combined criterion: the Zienkiewicz-Zhu error estimator in the elastic regime and the scalar error indicator in the non-linear regime.

Important

The error on the element level is evaluated using the element’s default integration rule. For the Zienkiewicz-Zhu estimator the error, in the L2 or the energy norm, is evaluated from the difference between the computed and the “recovered” stresses, which are approximated with the same interpolation functions as the displacements. In many cases the default integration order is therefore not sufficient and a higher integration order must be used on the elements — see the Element Library Manual and the element’s nip parameter.

Parameters of EET_SEI

Syntax

vartype (in) minlim (rn) maxlim (rn) mindens (rn) maxdens (rn) defdens (rn) [regionskipmap (ia)] [remeshingdensityratio (rn)]

Parameters

[regionskipmap (ia)]

Allows some regions to be skipped: the error is not evaluated there and the default mesh density is used. Its size should equal the number of regions, and a nonzero entry marks a region to skip.

vartype (in)

Type of internal variable used as the error indicator. The currently supported value is 1, a damage-based indicator.

minlim (rn), maxlim (rn), mindens (rn), maxdens (rn), defdens (rn)

If the indicator value lies in the range (minlim, maxlim), the proposed mesh density is interpolated linearly within the range (mindens, maxdens). If the indicator value is less than minlim, defdens is used as the required density; if it is larger than maxlim, maxdens is used.

[remeshingdensityratio (rn)]

Allowed ratio between the proposed and the actual density. Remeshing is forced whenever the actual ratio falls below this value. Default 0.80.

Parameters of EET_ZZEE

Syntax

normtype (in) requirederror (rn) minelemsize (rn) [regionskipmap (ia)]

Parameters

[regionskipmap (ia)]

As for EET_SEI.

normtype (in)

Type of norm used when the error is evaluated: 0, the default, uses the L2 norm, 1 uses the energy norm.

requirederror (rn)

Required error to reach, as a fraction — that is, percent divided by 100.

minelemsize (rn)

Minimum limit on the element size.

Parameters of EET_CZZSI

The union of the EET_SEI and EET_ZZEE parameters. The inelastic regions are driven by EET_SEI, the elastic ones by EET_ZZEE.