FEA Input Files

The following are all the possible sections for input XML files for running NairnFEA. When input files are validated using the DTD file (as recommended), the sections must appear in this specified order. Optional sections that are not needed may be omitted. A sample NairnFEA input file shows a sample calculation of a cantilever beam.

XML File Overview

All input files for FEA calculations are XML files. When using NairnFEAMPM or NairnFEAMPMViz to set up calculations using a scripting language, the XML file is created for you by interpreting the scripting commands (and you can skip this section). If you are manually writing XML files, however, it must follow the structure defined in this section.

All XML command files for FEA calculations must begin with an XML declaration, an optional document type declaration, and the main input file tag and end with the corresponding closing tags. For FEA calculations, the global file structure is:

<?xml version='1.0'?>
<!DOCTYPE JANFEAInput SYSTEM "NairnFEA.dtd"
[
  <!ENTITY force "100">
]>
<JANFEAInput version='3'>
   ...
   (XML Commands to define the calculation)
   ...
</JANFEAInput>

The !DOCTYPE element defines the file type and has the SYSTEM option to provide a path to a Document Type Definition (or DTD) file. The path is needed when you run the code with the validation option (-v), which is highly recommended. The required DTD file for FEA calculations is provided in the /input folder of the source code files.

The !DOCTYPE element can define any number of entities. These entities can be used elsewhere in the text of the XML file and they will be replaced by the text in the entity definition. Entities can define values that make it easier to read input XML files and easier to modify them for new calculations.

The remainder of the file is included within a JANFEAInput block. The version attribute is currently not needed, but may be important in the future. To be consistent with the document definition in the DTD file, all elements with the JANFEAInput block must be entered in the ordered defined in the table of contents on this page. Elements that are not used can be omitted, but all needed elements must be in that specific order.

Header

This section, which is required in XML files, defines the type of analysis to be done. In XML files, the header block is

<Header>
  (commands)
</Header>

When using scripting language, the header is created by commands in this section. The possible header commands are

• Analysis Command
• Description Command
• Controlling FEA Output
• Setting Developer Flags

Defining Materials

Each element in the mesh is assigned a material type. NairnFEA support numerous material models, but currently all are linear elastic. The information on these materials is found in are in FEA Material Models.