Loads

A load applies a force or a flux to the model. Loads are Neumann conditions, as distinct from the boundary conditions, which prescribe values instead.

Loads belong to a step. A load defined in one step does not carry into the next unless it is defined there too, which is how a load is removed partway through an analysis.

Assigning a load

Expand the load type in the tree, set its values, and select the entities it applies to. The types available are:

Load type	Applies to
Gravity	Surfaces, volumes
Point load	Points
Pressure	Lines, surfaces
Water Pressure	Lines, surfaces
Drainage	Lines, surfaces
Ground springs (Winkler)	Solid edges, solid faces or beams
Compliant base	Lines, surfaces
Inflow/Outflow	Lines, surfaces
Mass point	Points, lines
Spring-damper element	Two node sets

Gravity takes a magnitude and a direction, and is what applies self-weight. It belongs in the geostatic step and in every step that follows — a step without gravity has no self-weight in it.

Point load takes a component per direction: x, y and z.

Loading rate

Every load carries a Loading rate:

Option	Meaning
instant	The full value is applied at the start of the step
amplitude	The value follows a named amplitude over the step

With amplitude selected, an amplitude is chosen from those defined in the amplitude manager, and an Edit amplitude command opens the manager directly from the tree.

Applying a large load instantly is a common cause of convergence trouble. A ramp amplitude applies it gradually and usually solves it. Gravity in a geostatic step is the exception — there the load is meant to be present from the outset, and instant is right.

Editing loads across steps

The tree is where a load is created. Once it exists, the load manager is the faster way to change it, because it shows every load of a step in one table and can carry an edit forward into the following steps in one action.

Use the tree to add a load or to change one in a single step; use the load manager when the same load has to be adjusted through a sequence of steps.

Loads are described under Distributed loads, Distributed surface loads, Cload, Body Force, Mass points and Spring-damper element in the numgeo reference manual.