MPM Input Files

MPM simulations are run using NairnMPM. Some of the key features of these code engines (with links) are listed here. The documentation on this page explains how to run MPM calculations by described all the sections of input command files.

Input Command File Overview

When using NairnFEAMPM or NairnFEAMPMViz to set up calculations, the input command files are usually script files written using the custom scripting language. When you interpret these scripts, the applications will create an XML input command file that is needed to drive the code engines. Click this link to see a sample scripted MPM input command file for simulation of two colliding disks.

Alternatively, you can directly create XML input command files. Because this approach cannot use the language control options of a scripting language, it is much less powerful then scripting methods and much harder to customize for a range of simulations. If you do use the manual XML method, the files must conform to the structure defined here. Click this link to see a sample XML MPM input command file for simulation of two colliding disks.

Main Header

This section defines the type of analysis to run and provides an optional description of the calculations. 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 - pick the type of MPM analysis to run.
• Annotation Commands - these commands let you annotate the calculations.
• Processors Command - pick number of processors for parallel code.
• Setting Developer Flags

MPM Header

This section defines many settings and features for the MPM calculations. When using a scripting language, the MPM header is created automatically by various commands defined in this section. When writing XML input files, all these commands must be within a single MPM header block:

<MPMHeader>
  (commands)
</MPMHeader>

The possible MPM header commands are given below by categories.

• MPM Methods and Simulation Timing - these commands determine the MPM method to use, the time step, and the maximum simulations time.
• MPM Archiving Options - these commands determine which results are archived and where they are saved.
• MPM Global Archiving Options - these commands determine which results are archived in a global results file.
• Multimaterial MPM - these commands configure the calculations to run in multimaterial mode.
• Crack Settings - these commands define various simulation features when using cracks.
• Diffusion Calculations - this command activates diffusion calculations.
• Damping Options - these commands set up grid-based damping options.
• LeaveLimit Command - this command determine what happens when particles leave the grid.

Creating the MPM Background Grid

Although is a particle method, it uses a background grid to calculations. In general, this grid is a regular grid of orthogonal elements with linear shape functions. The background grid is easily generatee with a few commands. NairnMPM does allow explicitly generated grids, but you should never use them because many important features of MPM rely on a regular grid and are only efficient for a regular grid (e.g., uGIMP and CPDI shape functions).

Using Explicit Cracks

An advanced feature of NairnMPM is that it can model explicit cracks including multiple cracks, interacting cracks, and crack propagation. To create a simultion with cracks, you first define the cracks and then optionally customize various settings of the crack modeling methods. To include crack propagation, you also need to set all needed material fracture properties.

Defining Material Models

Each material point is assigned a material type. NairnMPM supports numerous material models. For plasticity materials, each material type can choose from among a set of hardening laws. Finally, when using explicit cracks, the material points along the cracks can be assigned to various traction laws. The information on these options are in the following sections:

• Material Models - all material models available for MPM simulations
• Hardening Laws - all hardening laws available for plasticity materials
• Traction Laws - all traction laws available for modeling cohesive zones on cracks

Thermal Calculations

MPM simulations can do thermal calculations that account for thermal strains in the stress analysis and can model thermal conduction. The commands in this section activate thermal calculations.

XML Insertion

When writing scripted input files, it is sometimes useful to insert raw XML commands into the automatically-format XML input file. The two commands that help in this task are:

• Entity Command - to define entities that will appear in the automatically-format XML input file.
• XMLData Command - to insert raw XML data into various sections of the automatically-format XML input file.