In combustion dynamics modeling, a mixed approach of using CFD and FEA is widely used. The use of FEA enables engineers to study the system dynamics in the frequency domain, which is an efficient approach compared to using CFD. The methodology essentially freezes the CFD solution at a given time, and then runs a frequency-domain finite element analysis based on the current CFD solution state. Since the finite element analysis models the fluid with acoustic elements, the density, temperature and flow velocity from the frozen CFD solution must be used in order to accurately model the fluid.

The velocities from the CFD analysis cannot be directly applied in the frequency-domain acoustic analysis, however. The workaround to this limitation involves defining dummy initial temperature conditions and then modifying them as described below.

1. Using the Abaqus output database of the CFD analysis, create three analytical fields: one each for V1, V2 and V3.
2. Create a predefined “Temperature” field and use the  analytical field for V1.
3. Repeat the previous step two additional times and use the analytical fields for V2 and V3, respectively.
4. Edit the model keywords and replace *INITIAL CONDITIONS, TYPE=TEMPERATURE with *ACOUSTIC FLOW VELOCITY.
5. Add the DOF direction to all the data lines under *ACOUSTIC FLOW VELOCITY.