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.

Introduction

This page documents all the options for the NairnFEA code engine. The capabilities and features of this code engine is embedded in the documentation of input commands for each option. Some highlights of capabilities (with links to input commands) are:

• 2D and axisymmetric calculations
• Many element options
• Meshes from images
• True periodic boundary conditions

Input Command File Overview

When using NairnFEAMPM or NairnFEAMPMViz to set up calculations, the input command files are script files. When you interpret these scripts, the applications will create an XML input command file that is needed to drive the code engines. Because the scripting language handles all the XML formatting, you can skip this section. See the help documentation in NairnFEAMPM or NairnFEAMPMViz for syntax and features of the scripting languages. Click this link to see a sample scripted FEA input command file for analysis of an end-loaded cantilever beam.

Alternatively, you can directly create XML input command files (although usually much less powerful then learning the scripting methods). If you use the manual method, the files must conform to the structure defined in this section. All XML input 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. Click this link to see a sample XML FEA input command file for analysis of an end-loaded cantilever beam.

Header

This section defines the type of analysis to run, provides an optional description of the calculations, and sets some output options. When using a scripting language, the header is created automatically and its content is controlled by commands defined below. When manually writing XML files, the header, which is required, is defined in a single header block:

<Header>
  (commands)
</Header>

The possible header commands are

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

Defining the FEA Mesh

FEA calculations are done within a mesh of elements. There are two ways to specify the mesh. The most common is to generate the mesh by defining keypoints and paths and then using them to mesh areas. The second mesh method is to explicitly define the mesh by defining every node and element. This uncommon method can only be used in XML input files. The generate and explicit methods cannot be mixed.

An advanced mesh generation option is to create the mesh with image and shape commands. When using this procedure, you first generate or explicit define a mesh and then using image and shape commands to define material types, define material angles, and create the final mesh geometry.

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.