MPM Input Files

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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

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.

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).

Creating the Material Points

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 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

Grid-Based Boundary Conditions

Velocity Conditions

Temperature Conditions

Concentration Conditions

Explicit Grid-Based Boundary Conditions

Particle-Based Boundary Conditions

Load and Traction Conditions

Concentration Flux Conditions

Explicit Particle-Based Boundary Conditions

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.

Gravitation Field

Custom Tasks

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.