MPoint Modeling • Introduction

Overview

MPoint is Itasca’s Material Point Method (MPM) software for modeling continuum-mechanics problems; MPoint3D and MPoint2D are the three-dimensional and two-dimensional implementations of MPoint, respectively. The software is designed to provide a general-purpose modeling environment for problems involving large deformation, material flow, contact, and failure. MPM represents the material with moving material points and uses a stationary background grid to solve the equations of motion. This combined Lagrangian–Eulerian formulation preserves material history while avoiding the progressive mesh distortion that can limit conventional Lagrangian methods at large deformation.

Each material point carries mass, volume, position, velocity, stress, strain, constitutive state, and material properties. During every calculation cycle, material-point information is mapped to nearby grid nodes, the nodal equations of motion are solved explicitly, and the updated nodal solution is transferred back to the material points. The material points then move through the grid and retain the evolving state of the continuum.

This formulation is well suited to large deformation, material transport, contact, separation, failure, and post-failure motion. Typical applications include slope failure, landslides, granular collapse, penetration, impact, excavation, and soil–structure interaction. Dynamic problems are solved directly using explicit time integration; quasi-static conditions may be approached by applying loading gradually and using suitable numerical damping to reduce inertial effects.

The MPoint2D and MPoint3D environments provide command-line, graphical, and FISH capabilities for generating material points, defining the background grid, assigning constitutive models and properties, applying boundary and initial conditions, controlling the solution, recording histories, and visualizing results.

Note

The concepts in this section generally apply to both MPoint2D and MPoint3D. Program-specific differences are identified where appropriate.

Important Modeling Objects

The principal objects used in MPoint2D and MPoint3D are summarized below.

Object	Role in a model
Material points	Represent the continuum and carry mass, motion, stress, deformation, constitutive state, groups, and material properties.
MPoint Nodes	Form the background grid, receive mapped quantities, enforce nodal constraints, and support damping and explicit time integration.
Zones	FLAC-style continuum zones used to construct geometry, initialize conditions, or create material points through zone conversion.
Hybrid points	Coupling objects used where zone-based and MPoint regions interact.
Walls and boundaries	Define external constraints or contact surfaces where supported by the selected modeling workflow.

Typical Command Sequence

Most MPoint2D and MPoint3D models follow the same general order. The details change from one problem to another, but the following sequence provides a useful starting point.

1.  Start a new model.
2.  Define the model domain.
3.  Define mpoint node spacing.
4.  Create or import geometry.
5.  Generate zones if zone conversion is used.
6.  Generate or import material points.
7.  Assign groups.
8.  Assign constitutive models.
9.  Assign material properties.
10. Apply gravity or loading.
11. Initialize stresses if needed.
12. Apply mpoint node boundary conditions.
13. Add damping if needed.
14. Define histories.
15. Cycle or solve the model.
16. Save, plot, export, and interpret results.

Nomenclature

MPoint2D and MPoint3D use terminology from continuum mechanics, explicit numerical methods, and particle–grid formulations. Program-specific terms and commands are defined throughout the documentation and in the command and FISH references.