Input Format¶

OASIS supports two input formats: the original ASCII (.dat) multi-file system and the newer YAML single-file format. Both provide the same functionality.

ASCII Format (`.dat`)¶

The traditional format uses multiple text files in the input/ directory, one per subsystem:

File	Content	Always required
`dataProblem.dat`	General simulation parameters (gravity, time steps, tolerances, solver)	Yes
`dataBodies.dat`	Body definitions (hydrodynamic database, DOFs, initial position)	Yes
`dataBCPs.dat`	Boundary condition points (anchors, fairleads, joints)	Yes
`dataWaves.dat`	Wave definition (type, spectrum, direction)	Yes
`dataLines.dat`	Mooring line properties (elements, stiffness, friction)	If lines used
`dataSprings.dat`	Spring/connector definitions	If springs used
`dataWinches.dat`	Winch mechanical properties	If winches used
`dataWinchesController.dat`	Winch controller parameters	If winches used
`dataSeaFloor.dat`	Seabed geometry definitions	If non-flat seabed
`dataSinking.dat`	Progressive flooding compartments	If sinking used

Each .dat file uses a simple line-based format where values are followed by comments:

9.81            // gravity [m/s^2]
1025.0          // waterDensity [kg/m^3]

Block separators use ////////////////// comment lines.

See Input Reference for the complete field-by-field specification of each file.

YAML Format¶

The YAML format consolidates all configuration into a single file: input/dataProblem.yaml.

problem:
  gravity: 9.81
  water_density: 1025.0
  water_depth: 50.0
  simulation_time: 300.0
  write_time_step: 0.1
  max_time_step: 0.1
  hydro_time_step: 0.1
  solver:
    method: 3          # ESDIRK46
    adaptivity: 0
    abs_tol: 1.0e-5
    rel_tol: 1.0e-3
    max_iter: 20

bodies:
  - type: RAD_DIFF
    database: ../../../data/one_box.hydb.h5
    database_index: 1
    dofs: [1, 2, 3, 4, 5, 6]
    position: [0, 0, 0, 0, 0, 0]
    freedom: 0          # 0=free, 1=locked, 2=imposed
    radiation: 1
    excitation: 1

bcps:
  anchors:
    - position: [200, 0, -50]
  body_bcps:
    - position: [10, 0, -5]

waves:
  type: IRR
  Hs: 2.0
  Tp: 10.0
  heading: 0.0
  ramp_time: 5.0
  spectrum:
    type: 1             # JONSWAP
    gamma: 3.3

Format Detection

OASIS checks for dataProblem.yaml first. If found, YAML format is used automatically. No command-line flag is needed.

BCP Type Mapping¶

The BCP (Boundary Condition Point) naming differs between formats. Here is the mapping:

ASCII name	YAML key	Class	Description
"Actuators"	`fairleads`	`FairleadBCP`	Prescribed-motion point (reads actuator file)
"Anchors"	`anchors`	`AnchorBCP`	Fixed anchor point
"Joints"	`joints`	`JointBCP`	Multi-line joint with mass/volume
"Fairleads"	`body_bcps`	`BodyBCP`	Point attached to a body
"Elastic Anchors"	`elastic_anchors`	`ElasticAnchorBCP`	Anchor with elastic spring

Warning

BCP indices are assigned sequentially in this order: fairleads (actuators) first, then anchors, joints, body_bcps, elastic_anchors. The same ordering applies in both ASCII and YAML formats.

Choosing a Format¶

Aspect	ASCII	YAML
Maturity	Original format, all features	Newer, all features supported
Readability	Comments describe each value	Self-documenting keys
File count	4–8 files per simulation	Single file
Editing	Simple text editor	Any YAML-aware editor
Existing examples	All examples have ASCII	~15 examples have YAML equivalents

Both formats can be used interchangeably. For new projects, YAML is recommended for its clarity.