Parametric procedure for 3D structural modeling of electrolysis cells.

 

Customer of this project is an international leading company in primary aluminum production. The aim is to make structural analysis of aluminum electrolysis cells as simple as possible and to allow quick changes and verifications. The set-up of a parametric model for a typical cell structure is also a powerful tool to investigate some advanced topics not yet well known, like cathode swelling.

The parametric structural model is a complete procedure to prepare and solve in a relatively easy manner a full 3D fem idealization containing an exceptionally high number of non-linearities of different type, such as: elasto-plastic and creep behavior, custom materials, very high temperatures and gradients, large deflections and tens of contacting surfaces.

A typical job is started through a pre-processor that constitutes the user interface for entering geometric parameters, material properties, loads and other environmental characteristics and solution options. The procedure is a collection of routines written in APDL Ansys language and Fortran. Due to the special mechanical behavior of carbon cathode material and electrolysis bath interaction, its solution requires the generation of a customized version of Ansys. The step-by-step solution may simulate the true operating life of a cell, covering a period of four or more years.

Constitutive laws controlling non-linear material behavior are defined within the Usermat routine, a newly introduced feature to customize Ansys, depending from user needs. In our case,  Usermat is actually a large package, coded in Fortran and linked with the Ansys object code, which contains a library of various expansion laws and stress-strain relationships. Usermat is called by Ansys at each substep and for each element integration point.