Boundary conditions

The boundary conditions block groups conditions by type. Each type key maps to a list of entries:

boundary conditions:
  Dirichlet:
    - node set: nsx-
      component: x
      function: "0.0"
    - node set: nsx-
      component: y
      function: "0.0"
  Neumann:
    - side set: ssz+
      component: z
      function: "1.0e+09 * t"

The block is optional; a model with no boundary conditions has none. This page covers the single-domain condition types. The Schwarz coupling condition types (Schwarz overlap, Schwarz DN nonoverlap, Schwarz impedance nonoverlap, Schwarz impedance overlap, Schwarz contact) are documented under Multidomain and Schwarz coupling.

The component value is always one of x, y, or z. The function value is a function expression in t, x, y, z. Geometry is selected by a node set or side set name from the Exodus mesh, as noted per type.

`Dirichlet`

Prescribes a displacement component. Velocity and acceleration follow by automatic time differentiation (see Function expressions).

Key	Required	Meaning
`node set` or `side set`	one required	geometry the condition acts on
`component`	yes	`x`, `y`, or `z`
`function`	yes	prescribed displacement

Dirichlet:
  - node set: nsz+
    component: z
    function: "0.01 * t"

`Neumann`

Applies a traction component over a side set.

Key	Required	Meaning
`side set`	yes	surface the traction acts on
`component`	yes	traction direction `x`, `y`, or `z`
`function`	yes	traction value

Neumann:
  - side set: ssz+
    component: z
    function: "1.0e+09 * t"

`Neumann pressure`

Applies a scalar follower pressure normal to a side set. There is no component — the direction is the surface normal.

Key	Required	Meaning
`side set`	yes	surface the pressure acts on
`function`	yes	scalar pressure (positive acts along the outward normal)

Neumann pressure:
  - side set: interior_ss_bottom
    function: "-937.5e3 * 1500 * (0.5 - 0.5 * cos(pi * t / 1500.0))"

`Robin`

A mixed condition traction + (robin parameter)·displacement = function on a side-set component.

Key	Required	Meaning
`side set`	yes	surface the condition acts on
`component`	yes	`x`, `y`, or `z`
`function`	yes	right-hand side
`robin parameter`	yes	coefficient on the displacement term (nonzero)

`Surface`

An inclined-support (roller) condition: the constrained nodes are held on the level surface g(x, y, z) = 0 given by function, free to slide within it. The constraint direction is the surface gradient ∇g, computed automatically; a constant function (no gradient) is rejected.

Key	Required	Default	Meaning
`side set`	yes	—	surface whose nodes are constrained
`function`	yes	—	level-set expression g in `x, y, z`
`enforcement`	no	`exact`	`exact` or `penalty`
`penalty`	no	`1.0e6`	penalty coefficient (positive; used when `enforcement: penalty`)

Canonical examples

Fixed and time-dependent Dirichlet: examples/single/static-solid, examples/single/implicit-dynamic-solid
Neumann traction: single-domain examples under examples/single/
Neumann pressure: pressurized cases under examples/ahead/