Initial-condition manager
Initial conditions describe the state of the model before the first calculation step: the stresses already present in the ground, the pore pressures, the density of the soil. Getting them right matters, because a model that starts out of equilibrium will move as soon as the analysis begins, regardless of the loads applied.
Open the manager from the numgeo tools toolbar or from numgeo → Manager → Initial conditions.
Note
The manager works directly on the data tree — there is no separate database file. The first time it is opened in a project, the old Initial conditions branch of the data tree is hidden, since the manager replaces it. Existing assignments are kept and remain fully editable; only the redundant nested editor disappears.
Window layout
Defined initial conditions on the left lists every assignment in the project. New, Duplicate, Delete and Refresh act on whole assignments.
The editor on the right has three sections:
Assignment — the name of the assignment and its type.
Groups — the entity groups the condition applies to. Preview draws the selected groups in the viewport so the extent can be confirmed before applying, and Stop preview clears the drawing.
Values — the parameters of the chosen type. The fields change with the type, and within a type with the selected option.
The button at the bottom changes with what you are doing: Create assignment for a new one, Create duplicate after duplicating, Update assignment when an existing record is selected. Clear editor resets the form.
Types of initial condition
| Type | Can be assigned to |
|---|---|
| Initial void ratio | Surfaces, volumes |
| Initial stress | Surfaces, volumes |
| Pore water pressure | Points, lines, surfaces, volumes |
| Pore air pressure | Points, lines, surfaces, volumes |
| State variable | Points, lines, surfaces, volumes |
Void ratio and stress are restricted to surfaces and volumes because they are properties of a material region rather than of a boundary.
Initial void ratio
A single value for the material region. Default 0.5.
Initial stress
The most involved of the types, with four options:
Geostatic — a linear vertical stress profile between two depths, with horizontal stresses derived from the lateral earth-pressure coefficients.
| Field | Default | Unit |
|---|---|---|
| Depth 1 | 0 | m |
| sigma_v at depth 1 | 0 | kN/m² |
| Depth 2 | -10 | m |
| sigma_v at depth 2 | -190 | kN/m² |
| k0,x | 0.5 | – |
| k0,y | 0.5 | – |
This is the usual choice for a soil profile. Note the sign convention in the defaults: depths below the surface are negative, and compressive stress is negative.
Full — a constant stress tensor applied to the whole region, given by its
six components sigma1, sigma2, sigma3, sigma12, sigma13, sigma23,
all in kN/m². Use it when the initial state is uniform and known, rather than
depth-dependent.
User — the stress state is supplied by a user routine.
File — the stress state is read from a numgeo binary restart file, which is selected with Browse....
Warning
A stress restart file can only be used when the mesh of the new simulation matches the mesh stored in the file. Remeshing invalidates it.
Pore water pressure / Pore air pressure
Both define a linear pressure profile between two depths:
| Field | Default | Unit |
|---|---|---|
| Depth 1 | 0 | m |
| Pore pressure at depth 1 | 0 | kN/m² |
| Depth 2 | -10 | m |
| Pore pressure at depth 2 | 100 | kN/m² |
The defaults describe a hydrostatic profile with the water table at depth 0.
State variable
Sets the initial value of a state variable of the constitutive model, with four options:
Default — a single value, applied uniformly. Requires the state-variable name and the value.
User — the values come from a user routine. The name is optional here.
Fluctuation — a randomly fluctuating field, defined by a maximum, a minimum and a correlation length in metres. Use it to represent natural variability of a soil property rather than a uniform value.
Spatial data — values read from a text file. The layout selects how the file
is interpreted: x-data, y-data, z-data, xy-data or xyz-data. The
filename is given without the .txt extension, and the file must be in the
calculation directory.
Note
The state-variable name must be the exact identifier expected by the constitutive model of the material. It is not validated against the model, so a misspelling will be silently ignored rather than reported.
Creating an assignment
- Press New.
- Give the assignment a name and choose the type.
- Select the groups it applies to, and press Preview to confirm the extent in the viewport.
- Fill in the values.
- Press Create assignment.
To change an existing one, select it in the list, edit, and press Update assignment.