Mesh and output files

input mesh file:  cube.g
output mesh file: cube.e
output interval:  1.0e-4

Path resolution

Relative paths are resolved against the directory containing the YAML input file, not the current working directory. Absolute paths are used as-is.

This means an input file referring to cube.g finds the mesh next to itself, so a simulation directory can be run from anywhere:

bin/carina examples/mechanics/quasistatic/cube/cube.yaml   # works from repo root

Both keys are required. Omitting either is a hard error:

Missing required input key: "input mesh file"

Mesh entities referenced elsewhere in the input — side set and node set names in boundary conditions and initial conditions, block names in body forces — must match names defined in the Exodus mesh.

Output interval and subcycling

output interval sets how often results are written — a time period in seconds, independently of the integrator's time step. When omitted it equals time step, giving one frame per step. It must be a positive number; zero, negative, or non-numeric values are a hard error.

The number of output frames is

num_stops = ceil((final time − initial time) / output interval) + 1

counting the initial state, which is always written. When the interval does not divide the time span, the last interval is partial: its stop is clamped to final time, so the full span is always simulated and the final state is always written. An interval larger than the whole span therefore writes exactly two frames — initial and final — which is the lean configuration for long runs and benchmarks where the per-step write cost matters.

When output interval is larger than time step, the integrator subcycles: it takes as many internal steps as needed to reach the next output time, and only then writes. This is the normal configuration for explicit dynamics, where a stable step may be nanoseconds while you want output every few microseconds.

time integrator:
  type: central difference
  time step: 1.0e-7
  final time: 1.0e-3
output interval: 1.0e-4        # 10 frames, ~1000 steps each

Carina reports which regime it is in at startup — either

[SETUP]   Time: [0, 1e-3], Δt = 1e-7, 10000 steps

when the interval equals the step, or

[SETUP]   Time: [0, 1e-3], Δt = 1e-7, output every 1.00e-04 (11 stops)

when it does not.

Landing exactly on output times

Output times are exact. Rather than take a sliver step to land on a stop, Carina stretches the last step of each interval: if the next full step would finish within half a step of the output time, the whole remaining gap is taken as one step instead. The actual step can therefore reach 1.5× the nominal Δt at the end of an interval.

For explicit runs this matters — a stretched step is still bounded by the stability limit only if your nominal Δt has headroom. Using the CFL key rather than a hand-tuned time step leaves that headroom automatically; see Time integrators.

With adaptive stepping enabled the integrator may additionally shrink or grow its step within an interval in response to solver convergence, independently of this snapping behaviour.

Output content

Which fields are written — and how element quantities are projected to nodes — is controlled by the separate output section, documented in Output fields.