Specification of geometrically nonlinear iteration control parameters (Input Table)
Table description:
Through the input data table GEOMCTL the geometrically nonlinear iteration process is given boundary conditions.
By means of the parameter MAXGIT the number of geometry iterations to be performed is given a maximum. In case of soil the higher of the parameters MAXSIT and MAXGIT will be decisive.
If the process fulfils one of the following equilibrium criteria, the geometry iteration process will stop.
RELDISEQ is the calculated ratio of relative disequilibrium of the overall pipeline structure and ABSDISEQ is the calculated ratio of the absolute disequilibrium of the overall pipeline structure relative to the external+ internal load vector norm. The ratios to the specified criteria for RELDISEQ and ABSDISEQ are reported in DISEQ, which is a truncated integer value. (e.g the real value 1.9 becomes 1)
ABSDISEQ is especially important if the loadings and hence the internal forces and reactions are very small (e.g. a one sided fixed elastic bend is released in 'free air', then loadings and reaction forces and internal forces are 'zero' in the equilibrium state). If DISEQ becomes '0' the geometry iteration process ends. The third parameter ROTINCR  a measure for the rotation increment of the overall pipeline structure  is used to avoid uncontrolled increase of rotations possibly resulting in instability of the pipeline model (especially if there is no soil). If the calculated ROTINCR is greater than the specified value, all calculated additional displacements are multiplied to meet the specified value. It is recommended to use the default parameter values.
RELDISEQ 
ABSDISEQ 

Default 
105 
107 
Recommended for upheaval buckling 
105 
107 
Designs where pipeline behaviour is less stable (difficult convergence) 
103 
105 
If the REDISOVL box has been ticked off, the ovalisation redistribution is switched on. It is recommended to redistribute the ovalisations in Design Function 5 in case of large occurring ovalisations and plastic deformations. Then redistribution in Design Function 6.1 only is not appropriate anymore.
The ovalisations and plastic deformations (strains) can be found in output table DEFORM.
This option is possible only if the Section Model has been set to "Ovalising" in Design Function 1. For more information on the Section Model see Model Options: Section Model.
H500132, last changed: 20080722
See also: