Tube case with Fluent2D and Abaqus2D - Steady

This example calculates the flow inside and the deformation and stresses of a straight flexible tube, when a steady pressure difference is applied over the tube. This done by using Fluent and Abaqus, both on an axisymmetric case.

The test example is similar in setup to tube_fluent2d_abaqus2d. The only difference is that a steady problem is simulated. Here the most important differences and peculiarities of a steady case are highlighted.

General settings

Although the calculation is steady, a delta_t is still required. Its value is arbitrary and usually 1.0 is used. timestep_start is required as well and is normally equal to 0.

Coupling algorithm

The coupling technique used is the interface quasi-Newton algorithm with an approximation for the inverse of the Jacobian from a least-squares model (IQN-ILS). The parameter q is not used as there is only one time step. Note that in a steady calculation, the models ls (IQN-ILS) and mv (IQN-MVJ) are identical.

Predictor

A predictor is still required, but not used as only one time step is calculated.

Solvers

Of course the supplied case files in both Fluent and Abaqus also need to be steady. In Abaqus this can be done using a Static step, typically with automatic time incrementation (subcycling) and a linearly ramped load. The parameter ramp is set to true in the json-file. As such Abaqus performs subiterations in each coupling iterations in which the load is increased linearly over the step. The ramping does not occur in Abaqus itself as, amplitude references are ignored for nonuniform loads given by user subroutine DLOAD in an Abaqus/Standard analysis. Instead, the ramping is implemented in the DLOAD subroutine itself. For the first iteration of the first time step an initial load is required which is set to zero in the Abaqus wrapper.