inp2feap

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Convert Abaqus .inp job files into input files for the research FEM code FEAP.

Overview

inp2feap is a lightweight python script allowing to convert (some) finite element meshes from Abaqus to FEAP. To get started, you need an Abaqus job file .inp and you must write a JSON-format configuration script, specifying how to process the input data.

As the most basic functionality, only nodal coordinates and element connections are converted from .inp file format to FEAP's coor and elem blocks. Optionally, header and footer files can be provided to add further instructions required by FEAP, as otherwise only an incomplete input file is written where nodes, elements and some boundary conditions are given.
In addition, boundary conditions can be automatically set on node sets (nsets) using the FEAP command boun. Element material numbers can be specified using Abaqus's element sets (elsets).

Example

Some simple examples are given in the example folder.

As a comprehensive example we consider a shell discretization of a representative unit cell in a honeycomb sandwich panel, where most available functionality of inp2feap is used. The Abaqus job file is given in examples/hex.inp, it contains all nodes and elements, three element sets (SET-ELEM_UNTEN, SET-ELEM_OBEN, representing upper and lower face layers of the sandwich panel, and SET-ELEM_WAENDE for the cell walls), as well as a node set SET-NODE-FHG6, specifying some nodes where additional boundary conditions have to be set.

example/hex.json is the accompanying configuration file for this input file.
Going through line by line, making sure to follow the JSON syntax:

• "input" : "hex.inp", Specify the Abaqus job input file to read from.
• "output" : "iHex", File to write to (FEAP input file).
• "nodesPerElem" : 4, Specify number of nodes per element (4-node quadrilateral here).
• "header" : "hex.head", Contents of this file will be inserted before any generated coor/elem blocks.
• "footer" : "hex.foot", Accordingly, contents of this file will be appended after any generated blocks. Here, the footer contains among other things the material definitions used in FEAP.
• "centerMesh" : true, Optional. Allows to translate the origin to the center of the bounding box of all nodes.
• "elsets" : [ { "name" : "SET-ELEM_UNTEN", "setMat" : 1 }, { "name" : "SET-ELEM_OBEN", "setMat" : 2 }, { "name" : "SET-ELEM_WAENDE", "setMat" : 3 }],
  Specify material number for all elements in element sets.
• "customInput" : { "block" : "vbou", "pos" : -1, "cards" : ["-99.,99.,-99.,99.,-99.,99.,0,0,0,0,0,1"]},
  Custom input allows to write any FEAP block and explicitly stating its input cards. With pos<0 the input is placed after coor/elem blocks, but before any automatically generated boundary conditions. This command locks the 6th DOF in the whole mesh.
• "nsets" : [{ "name" : "SET-NODE-FHG6", "setBoun" : "0, 0, 0, 0, 0, 0" }],
  A boun block will be written, containing an input card for all nodes in this node set and freeing all b.c.s (i.e. freeing the 6th DOF again but only on intersection nodes).

Note: All file paths are relative to the .json config file.

To build the according FEAP input file for this example, just type:
python inp2feap.py ../example/hex.json

Limitations and issues

As of now, inp2feap has only been tested with some elements, such as 3d 4-node quadrilaterals or 20-node volume elements.
In theory, elements with an arbitrary number of nodes can be used as long as a FEAP element is present with a compatible node numbering. For 2d models, however, the code must be modified.

Mixing elements with different numbers of nodes is not supported. inp2feap can not distinguish between different parts in a job file, so keep those simple. Only nodes, elements, nsets and elsets will be read from the input file, nothing else (like boundary conditions, loads, etc.)

Config file documentation

Config files must follow valid JSON syntax. Some error handling is present for required/optional parameters as well as data types.

See examples/hex.json for an example config file with most required and optional parameters or the other, more simple examples in the same folder.

The following parameters can be used to specify inp2feap's behavior:

• "input" - required. Abaqus job file (.inp) from where the mesh will be read.
• "output" - required. File to write the output (the FEAP input file) to.
• "header" - optional. Contents of this file will be inserted before any generated coor/elem blocks. Could contain the feap command and specifying a solver (solv).
• "footer" - optional. Contents of this file will be appended after any generated blocks. Could contain additional boundary conditions, loads, mate and macr blocks for FEAP.
• "nodesPerElem" - optional. Specify number of nodes per element. Meshes with elements with different numbers of nodes are not yet supported. Can be omitted, in which case the number of nodes is automatically determined. In case anything goes wrong, try to specify it explicitly. inp2feap might have trouble reading elements with many nodes if "nodesPerElem" is not explicitly specified.
• "elsets" - optional. If specified, must contain an array of element sets which each have a "name" (string) and "setMat" (int) parameter. inp2feap will look for elsets with the given name in the input file and assign the given material number to all elements in that elset.
  May have optional "duplicate" (int) parameter - if given, elements in this set will be duplicated using the specified int as new material number. This can be used for the FEAP loading element 30. Elements may be duplicated multiple times if multiple "duplicate" parameters are given.
  A warning will be issued should an element set specified in the config file not be found in the job file.
• "nsets" - optional. If specified, must contain an array of node sets which each have a "name" (string) and may have "setBoun" (string) and "setLoad" (string) parameters. If "setBoun" is given, a boun block will be written to the output file, where each node in this node set has its boundary conditions set to the value of "setBoun". Accordingly, with "setLoad" FEAP load blocks will be written for each node in this set. Consult the FEAP manual for information on how the syntax must look like.
  A warning will be issued should a node set specified in the config file not be found in the job file.
• "customInput" - optional, may occur multiple times. If specified, must contain a child object with "block" (string), "pos" (int) and "cards" (array of strings) parameters. "block" should be a FEAP mesh command (e.g. "vbou") which will be written to the output file, using the input cards "cards". If "pos"<0, the block will be written in between elem blocks and automatically generated boun blocks from "nsets". For "pos">0, the block will be written after the boun blocks but before the footer. Multiple "customInput"s will be written in ascending order of their "pos".
• "centerMesh" - optional (true/false). If specified and true, the origin of the coordinate system will be translated to the center of the bounding box of all nodes.