Dimension manager
The problem dimension decides how the model is interpreted: whether a surface is a slice through a long structure, a section rotated about an axis, or a face of a three-dimensional body. It also governs which element types, conditions and generators are available, which is why it is asked for first.
The window asks one question and closes as soon as it is answered. Clicking a card selects that dimension; there is no separate confirm step.
The three dimensions
| Dimension | Interpretation |
|---|---|
| 2D (plane strain) | A slice of unit thickness through a body that continues unchanged out of plane |
| 2D axisymmetric | A section rotated about a vertical axis |
| 3D | A full three-dimensional body |
2D (plane strain) suits anything long and prismatic — an embankment, a retaining wall, a strip footing, a tunnel in cross-section. Strain out of plane is zero, which is the assumption that makes the slice representative.
2D axisymmetric suits anything rotationally symmetric about a vertical axis — an axially loaded pile, a circular tank, a cone penetration test. The model is an r–z section, and the third dimension comes from the rotation.
3D is needed when neither symmetry holds: a laterally loaded monopile, a pile group, an excavation corner, layers that are not horizontal.
When it opens
The dimension manager opens by itself shortly after the problemtype is loaded, if the project has no dimension set yet. It does not reappear once a dimension has been chosen.
It can be reopened at any time from numgeo → Manager → Dimension. When it is, the dimension currently in force is highlighted.
Changing the dimension later
Changing dimension partway through a model is possible but disruptive. The element types and conditions available differ between dimensions, so assignments made under one may not be valid under another, and geometry built for a 2D model is not what a 3D model needs.
Set the dimension before building the geometry, and treat a later change as a reason to check the assignments through rather than as a simple switch.