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CONVENTIONS.md

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SEA-Stack Verification Data Conventions

This document defines the canonical conventions for all normalized verification data in SEA-Stack. Every file under data/verification/*/normalized/ must conform to these rules.

Units

All quantities use SI units:

Quantity Unit Notes
Time s Starting at 0
Length / heave m Displacement relative to equilibrium
Angle / pitch rad Right-hand rule about Y axis
Force N
RAO (linear) m/m Dimensionless
RAO (angular) rad/m Not deg/m
Frequency rad/s

Reference Frame

  • Global, right-handed, Z-up.
  • Origin at mean water level (MWL), centred on the device.
  • Displacements are relative to equilibrium, not absolute CG position. For example, sphere decay heave is "metres above equilibrium", not the global Z coordinate of the CG.

Sign Conventions

DOF Positive direction
Heave Upward (+Z)
Surge Forward (+X, wave propagation direction)
Pitch Bow-up (right-hand rotation about +Y)
Tension Positive = tensile

Phase Convention (RAO)

Phase is measured relative to cos(omega * t), positive = lead.

File Format

Every normalized .txt file must use the standard #-prefixed metadata header:

# SEA-Stack Verification Data
# format: timeseries | rao
# source: <tool_identifier>
# model: <case_name>
# quantity: <what_is_stored>
# units: <comma-separated SI units>
# columns: <space-separated column names with units>

Optional additional # comment lines may follow.

Numeric data is space-delimited, one row per time step (or frequency point).

Manifest Requirements

Every manifest.json must include for each normalized dataset:

  • coordinate_frame (e.g. "global, Z-up")
  • sign_convention (e.g. "positive up")
  • units dict mapping column names to SI units