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Analysis Types in openCFS

Several different analysis types are possible in openCFS. This is illustated in this tutorial by the example of a solid mechanics problem of a cantilever beam. In a single openCFS input file different analyses can be collected by defining several <sequenceStep index="N"> tags, which will run in sequence.

Typical analyses for the mechanic PDE are:

  • The static analysis computes equilibrium configuration (i.e. the defomation) of the beam for a stationary (static) load.

  • The eigenFrequeny step computes the natural frequencies and corresponding oscillaion modes of the beam.

  • The harmonic analysis computes the steady state response of the structure subject to harmonic loading.

  • The transient step computes the time dependent response of the structure subject to general, time-depedent loading.

Sketch of the domain


     CCCCC                                          
    CCCC/C                                          
  CCCC///C                                          
CCCC/////C                                          
CCC//////C                                          
CCC/////8000000000000000000000000000000000000000000008888   ^      ^
CCC///8              cantilever beam                   8    | h   / 
CCC/800000000000000000000000000000000000000000000008888     v    / b
CCC/80000000000000000000000000000000000000000000008888          /
CCC//<----------------------L------------------------>         v
CCC//////C
CCC/////C
CCC////C
CCC///C
CCCC


Sketch of the domain

Meshing

  1. Type 'trelis -batch -nographics -nojournal beam.jou' on the terminal.
  2. The journal file beam.jou from (1.) is used as an input.
  3. Both an ANSYS-cdb mesh file beam.cdb and a Trelis file beam.trelis are created.
  4. Look into the journal file beam.jou to see the Trelis commands to create the mesh.
  5. These commands could also have been run interactively in Trelis.
  6. Look through the mesh file to obtain the beam dimensions.

The file beam.cdb was created this way.

Simulation with CFS

The CFS input file is simulation.xml. It contains several analysis steps (static, natural frequency, harmonic, transient). The material file is called mat.xml using the usual convention.

To run the simulation execute

cfs -p simulation.xml job

which creates text files in history and the HDF5 output in results_hdf5/job.cfs. Both above steps can be done by running the shell scipt run.sh, i.e. in a terminal change to this directory and run

./run.sh

An an exercise:

  • Look into the material file to obtain the material properties
  • Study the CFS input and get familiar with each analysis step (step definition, BCs, loads, outputs)

Postprocessing

CFS can write output in various formats. In this example we define text-based history output and field output in the HDF5 format (*.cfs file).

As an exercise:

  1. Look at the produced ASCII file in history
  2. Load the result in ParaView and try the following things
    • Load the correct analysis step (=multi sequence step)
    • Display deformed geometry (use the Wrap by Vector filter)
    • Switch the Complex Mode for complex valued results
    • Animate Harmonic / Modal Results for the corresponding sequence steps
    • Animate transient results

Furter Sugesstions

  • Compare the results with the analytic solution
  • Specify a spacially varying load
  • Compute the natural frequencies of a free-free beam
  • Plot the results in the ASCII file (response of the end-point as a function of time and frequency, respectively)
  • What happens if you play with the damping parameter?
  • Which effect does the parameter T have?