Read a node's displacement and reactions¶

Pull a displacement or reaction-force time history out of a finished run, targeting nodes by physical-group name. This is the bread-and-butter post-processing read: open the results file, ask one composite for one component, index .values.

The shape in one line:

Results.from_native(path, model=...) → results.nodes.get(pg=, component=) → a frozen slab with .values (T, N), .node_ids, and .time.

Recipe¶

from apeGmsh import Results
from apeGmsh.opensees import OpenSeesModel

# Every Results constructor REQUIRES the read-side broker (model= /
# model_h5=); omitting it raises TypeError (ADR 0020 INV-1). Pass fem=
# too so pg=/label= name-resolution works against your session mesh.
model = OpenSeesModel.from_h5("model.h5")
results = Results.from_native("run.h5", model=model, fem=fem)

# --- Displacement: u_y history at every node in PG "Top" ---
disp = results.nodes.get(pg="Top", component="displacement_y")
disp.values        # ndarray (T, N) — one column per node in "Top"
disp.node_ids      # the matching node IDs, same column order
disp.time          # (T,) time/pseudo-time axis

u_y_final = disp.values[-1]          # last step, all nodes -> (N,)
u_y_node0 = disp.values[:, 0]        # full history at the first node -> (T,)

# --- Reaction: total base reaction in y, summed over PG "Base" ---
react = results.nodes.get(pg="Base", component="reaction_force_y")
Ry = react.values[-1].sum()          # last-step sum over the base nodes

nodes.get(...) is keyword-only: pg= / label= / selection= / ids= pick which nodes (named selectors union), component= picks what, and time= slices the step axis (time=-1 for the last step, time=[0, 50, 99] for specific steps). Component names are the canonical apeGmsh vocabulary: displacement_x/y/z, reaction_force_x/y/z, velocity_*, acceleration_*.

Notes / gotchas¶

Reactions must be recorded. reaction_force_* only exists in the file if you asked for it on the write side — e.g. spec.nodes(components=["displacement", "reaction_force"], pg="Base") (capture) or the equivalent recorder declaration. If the read comes back empty, the component was never captured. Call results.nodes.available_components() to see what's actually there.
model= is mandatory; fem= is for names. Without model= the constructor raises TypeError. Without a bound fem, the embedded /model/ snapshot resolves IDs but pg=/label= may miss session-side labels — pass fem= (or results.bind(fem)) and target by name.
.values is (T, N) — index, don't iterate. Last step is values[-1]; one node's history is values[:, j]. For a single-node PG it's still 2-D: values[:, 0].
Sum reactions, don't average. A support reaction is a force per node; the support's total reaction is .values.sum(axis=1) over the base PG (often negated to compare against applied load).
Target names, never raw tags. pg="Base" is stable across remesh and boolean ops; a hard-coded node tag is not.

Read a node's displacement and reactions¶

Recipe¶

Notes / gotchas¶

See also¶