Tech Briefs

Using NASTRAN Models for 3D CFD and FSI Analyses

The powerful features for CFD and FSI analyses available in ADINA can directly be used with NASTRAN models in ADINA 8.4. Hence I-deas, Femap, Patran, Hypermesh and other NASTRAN pre-processors can be employed to generate the model and the solution is performed using ADINA.

A particular feature — very important for transient analyses — is that the good mesh quality originally available in the NASTRAN model can be preserved throughout the ADINA solution, resulting in accurate solutions.

The typical solution process is as follows:

  • Generate the mesh for the CFD or FSI model in the pre-processor of your choice (e.g., I-deas, Femap, Patran, Hypermesh).

  • Export the NASTRAN model file from the pre-processor.

  • Import the NASTRAN model into the ADINA User Interface (AUI).

  • In the AUI, specify boundary conditions and loads using the surface data information and add some control data for the CFD or FSI solution.

  • Obtain the ADINA solution of the model.

ADINA 8.4 will offer this feature for CFD, and for fully-coupled or one-way coupled FSI solutions.

The 'fully-coupled FSI' solutions can be obtained 'directly-solved' with the sparse solver or 'iteratively-solved' using the iterative solvers. The same solutions are obtained and the choice is merely one of computational efficiency. The 'one-way coupled solutions' can also be obtained using either the sparse solver or the iterative solvers. Large models require in all cases the use of the iterative solvers.

The movie at the top of this page shows the results for the transient analysis of a shock absorber. The CAD model of the shock absorber is displayed in the figure above, where we also show the 3D finite element model for the fluid and structural parts that were imported from a NASTRAN model file. During a typical cycle, the piston pushes the fluid through about one-third the length of the shock absorber, and the fluid is squeezed through opening and closing valves. Hence very large mesh deformations are present. The movie below shows a detail at the lower valve, and in the last figure, the calculated force on the shock absorber is shown during a typical cycle.

The objective of the analysis is to obtain improved and optimum designs of shock absorbers. Further on-going analyses of the shock absorber using more detailed models are being carried out by the ADINA user.

For more information on ADINA FSI, please refer to our page on fluid-structure interaction.