Approach and Project Setup

A successful MPoint analysis begins with a clear statement of the engineering question. Decide whether the required result is a displacement, stress, runout distance, vibration response, collapse mechanism, contact force, or factor of safety. The required result determines the model dimensions, constitutive model, loading sequence, output histories, and acceptable level of numerical refinement.

Choice of MPoint2D or MPoint3D

Use MPoint2D when the geometry, loading, and expected response can be represented adequately by a two-dimensional idealization. Use MPoint3D when out-of-plane geometry, confinement, load spreading, torsion, or three-dimensional failure mechanisms are important. A thin MPoint3D model with out-of-plane velocity constraints may be used to approximate plane strain, but the intended idealization should be documented.

Project file organization

Separate model construction, solution stages, and figure generation when the project is large. A common project structure is:

project/
   setup.dat
   gravity.dat
   loading.dat
   plots.dat
   results/
   documentation/

Use model save after expensive or reusable stages and model restore to begin later investigations from a known state. This reduces run time and makes the loading history explicit.

Starting a model

The command model new clears the current model. The command model title assigns a descriptive title. The command model domain defines the region in which material points and background nodes may exist. The command model large-strain determines whether large strain is allowed or not by setting it to on or off. The default value is off.

model new
model title 'MPoint problem-solving example'
model domain extent 0 20 0 10
model large-strain on

For MPoint3D, provide three coordinate intervals:

model domain extent 0 20 0 5 0 10

Use large-strain mode for runout, penetration, collapse, excavation, impact, contact, and other problems involving significant motion. Small-strain mode may be useful during a preliminary gravity stage when geometry updates are not wanted, provided the later change to large strain is physically and numerically consistent.

Units and parameters

MPoint does not impose a unit system. Use one consistent system throughout the model. Define dimensions, densities, stiffnesses, strengths, gravity, loading rates, damping values, and solution controls near the beginning of the data file with simple command lines or using FISH variables. See Sign Conventions for details.

[gravity_magnitude = 9.81]
[node_spacing      = 0.25]
[mp_resolution     = 2]
[soil_density      = 2000.0]
[soil_young        = 50.0e6]
[soil_poisson      = 0.30]