Preprocessing

4C reads the mesh, boundary conditions, materials and simulation parameters from a central input file.

Under development

A large refactoring effort is currently in progress to improve 4C’s input files. The information in this section is not fully updated to reflect these changes.

There are not so many means to create a valid input file. At this point, we know of the following different ways to create an input file. In general, you’ll have two options:

  1. Either you create the input file in 4C’s native format directly,

  2. or you create an input file in a general binary format for finite element information, called Exodus II, develeloped by Sandia National Laboratories. This can be read into 4C via its input file.

Generating Exodus II files

Even though the generation of Exodus II files might be out of scope of a 4C manual, users are informed on how to generate these files conveniently, so options are given in the following:

CUBIT

CUBIT http://cubit.sandia.gov/ is a powerful pre- postprocessing tool. (The commercial version of the software was called Trelis, but has been renamed into CUBIT now as well, so we may stick to the name CUBIT).

Cubit allows you to create the geometry, mesh, and necessary node sets and export them to the EXODUS file format.

Note that

  • it is not necessary to define boundary conditions in Cubit, since they are not converted to the dat file later on.

  • you should only define node sets, but not sidesets (surface sets). The node sets are converted into surface sets if the surface definition is given in the boundary condition control file (<problem>.bc) anyway.

Other Software

Geometry as well as element and node sets can be created in any finite element preprocessor. However, the preprocessor should be capable of exporting a file format, which can be converted by the python toolset meshio (see <https://pypi.org/project/meshio/>) into an exodus file, with which the input can be converted into a 4C .dat file.

Also, the exported input file can probably be imported in Cubit, then further edited and eventually exported as an exodus (.e) file.

So the steps are

  1. Create finite element model and sets in your favorite preprocessor

  2. Export to some format, like Exodus II or the Gmsh format .msh file.

  3. Optional: Read in the model to Cubit for further editing

  4. Optional: If you are not able to write in Exodus II format, use the python module meshio (packed in pip) to convert the mesh to an exodus (.e) file (<https://pypi.org/project/meshio/>)

Other ways to create a 4C input directly

ABAQUS

There is an in-house Python module abaqus_meshio for the conversion from an ABAQUS input file (.inp) to dat file. This python module is available in the scripts gitlab. Since the .inp file can also be generated using Cubit, this submodule can be used in conjunction with Cubit as well, see above. The usage of this submodule starts firstly by importing it providing the path where it is located.

import sys

abaqus_meshio_path = "path_to_abaqus_meshio"
sys.path.append(abaqus_meshio_path)

Subsequently, the inp shall be read using the command

model = abaqus_meshio.read("path_to_inp.dat")

Unlike meshio.read, the command abaqus_meshio.read will return a model, which is instance of BModel, where:

  • model.rootAssembly.instances[instance_name].mesh is a BMesh. ``BMesh is a subclass of meshio.Mesh with additional attributes sections (for material assignment) and surfaces (for distributed load).

  • model has attributes materials (from MATERIAL), parts (from PART/END PART) and steps (from STEP)

  • model.parts[part_name].mesh is again a BMesh, model.rootAssembly.instances[instance_name].mesh is a transformation of this mesh.

BModel is designed to mimic the way Abaqus systematically stores its data. To access the original meshio.Mesh one has to use model.parts[part_name].mesh.

Proving that the information from inp is properly stored, the transformation to dat file is done by a simple command

fourc_io = abaqus_meshio.Inp2Baci(model, [params_step_1])
fourc_io.write("prefix")

If the inp has many steps defined by STEP/END STEP keywords, the list of parameters for each step has to be provided, e.g. [params_step_1, params_step_2, ...]. Default parameters for a structural analysis can be obtained using

params_step_1 = abaqus_meshio.GenerateDefaultParams()

Modify 4C input files

4C input files are text files so you can modify them using your favorite text editor. You can see all possible parameters and keywords in the reference part.