Mechanics Module Conversion Tips

Migrating an existing solid mechanics input file to use tensor mechanics is not always a straight-forward process. Although getting a migrated tensor mechanics input file to run successfully can be quickly achieved, analysts should ensure that the new tensor mechanics simulation results match those from the original solid mechanics simulation.

In some cases differences between the tensor mechanics and solid mechanics simulation results indicate an improvement in the tensor mechanics system from the solid mechanics system. Analysts should be certain that they both understand the source of the difference in simulation results and find the tensor mechanics simulation results more realistic before accepting differences in the results.

Different Defaults

One source of discrepancy in the simulation results can be the different default settings used in the solid mechanics module compared to the tensor mechanics module. Listed below are some of the different input file settings to double check for differences.

Volumetric Locking Correction

The Volumetric Locking Correction uses a formulation to prevent locking of elements.

In the tensor mechanics module, the Volumetric Locking Correction is set to false by default but in the solid mechanics module Volumetric Locking Correction is set to true by default.

Strain Formulation Defaults

The tensor mechanics module always defaults to using a small linearized strain formulation while the solid mechanics module default changes based on the geometry. Analysts are advised to always specify the strain formulation in the solid mechanics module materials and to use the TensorMechanics MasterAction in the tensor mechanics input file with the strain parameter set.

Relocation Activation Value 1 Default

Recent experimental work (Swiler et al., 2013) supports changing the default value from the 19685 W/m (6kW/ft) used in original ESCORE model (M. A. Kramman, 1987) to 5000 W/m (1.52 kW/ft) to better match experimental IFA data (Swiler et al., 2013).

The tensor mechanics module uses the new 5000 W/m as the default value while the solid mechanics module still uses the old 19685 W/m as the default setting.

Volumetric Strain Material Property

At present the calculation of the volumetric swelling eigenstrain material property differs between the two mechanics modules: (1) The difference in these quantities is resolved within the calculation of the total strain, but analysts should be aware of this difference in the material property. The Bison team is working to resolve this issue.


  1. Eds. M. A. Kramman, H. R. Freeburn. Escore–the epri steady-state core reload evaluator code: general description. Technical Report EPRI NP-5100, Electric Power Research Institute, February 1987.[BibTeX]
  2. L. P. Swiler, R. L. Williamson, and D. M. Perez. Calibration of a fuel relocation model in BISON. In Proceedings of the International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering. Sun Valley, Idaho, May 5-9, 2013.[BibTeX]