---

name: catenary-riser description: Analyze catenary and lazy wave riser configurations for static shape, forces, and OrcaFlex model generation. Use for riser static configuration analysis, catenary force calculations, lazy wave design, and generating OrcaFlex models from catenary parameters. updated: '2026-01-07'

Catenary Riser Analysis Skill

Analyze catenary and lazy wave riser configurations for static shape, forces, tension distribution, and OrcaFlex model generation.

Version Metadata

Copyversion: 1.0.0
python_min_version: '3.10'
dependencies:
  orcaflex-modeling: '>=2.0.0,<3.0.0'
orcaflex_version: '>=11.0'
compatibility:
  tested_python:
  - '3.10'
  - '3.11'
  - '3.12'
  - '3.13'
  os:
  - Windows
  - Linux
  - macOS

Changelog

[1.0.0] - 2026-01-07

Added:

• Initial version metadata and dependency management
• Semantic versioning support
• Compatibility information for Python 3.10-3.13

Changed:

• Enhanced skill documentation structure

When to Use

• Catenary riser static analysis
• Lazy wave catenary design and optimization
• Riser static configuration calculation
• Catenary force and tension analysis
• Generating OrcaFlex models from catenary geometry
• Fatigue loading extraction from riser configurations
• Pipe property calculations (buoyancy, effective weight)

Prerequisites

• Python environment with digitalmodel package installed
• Riser geometry and material properties
• Environmental data (water depth, current if applicable)

Analysis Types

1. Simple Catenary Analysis

Copycatenary:
  simple_catenary:
    flag: true
    geometry:
      top_end:
        x: 0.0
        z: 100.0
      touchdown:
        x: 500.0
        z: 0.0
    properties:
      outer_diameter: 0.2032
      wall_thickness: 0.0127
      steel_density: 7850
      internal_fluid_density: 800
      seawater_density: 1025
    output:
      shape_file: "results/catenary_shape.csv"
      forces_file: "results/catenary_forces.csv"
      plot_file: "results/catenary_plot.html"

2. Lazy Wave Catenary

Copycatenary:
  lazy_wave:
    flag: true
    geometry:
      water_depth: 1500.0
      hang_off_angle: 8.0
      buoyancy_section:
        start_arc_length: 800.0
        end_arc_length: 1200.0
        buoyancy_factor: 1.5
      target_sag_bend_depth: 800.0
      target_hog_bend_depth: 600.0
    pipe_properties:
      outer_diameter: 0.273
      wall_thickness: 0.0159
    output:
      configuration_file: "results/lazy_wave_config.csv"
      plot_file: "results/lazy_wave_plot.html"

3. OrcaFlex Model Generation

Copycatenary:
  orcaflex_model:
    flag: true
    catenary_config: "results/lazy_wave_config.csv"
    orcaflex_settings:
      line_name: "Riser1"
      segment_length: 5.0
      include_buoyancy_modules: true
    output:
      yml_file: "models/riser_model.yml"

Python API

Simple Catenary Equation

Copyfrom digitalmodel.modules.catenary.catenary_equation import CatenaryEquation
import numpy as np

catenary = CatenaryEquation()
top_end = (0.0, 100.0)
touchdown = (500.0, 0.0)

horizontal_tension = catenary.solve(
    top_end=top_end,
    bottom_end=touchdown,
    unit_weight=500.0
)

arc_lengths = np.linspace(0, catenary.total_length, 100)
x, z = catenary.get_shape(arc_lengths)
tensions = catenary.get_tension(arc_lengths)

Catenary Riser Analysis

Copyfrom digitalmodel.modules.catenary.catenary_riser import CatenaryRiser
from digitalmodel.modules.catenary.pipe_properties import PipeProperties

pipe = PipeProperties(
    outer_diameter=0.2032,
    wall_thickness=0.0127,
    steel_density=7850,
    internal_fluid_density=800
)

riser = CatenaryRiser(pipe_properties=pipe)
results = riser.analyze(
    water_depth=1000.0,
    hang_off_angle=10.0,
    top_tension=1500e3
)

print(f"TDP position: x={results['tdp_x']:.1f}m")
print(f"Total length: {results['total_length']:.1f} m")

Lazy Wave Catenary

Copyfrom digitalmodel.modules.catenary.lazy_wave_catenary import LazyWaveCatenary

lazy_wave = LazyWaveCatenary()
config = {
    "water_depth": 1500.0,
    "hang_off_angle": 8.0,
    "buoyancy_section": {
        "start_length": 800.0,
        "end_length": 1200.0,
        "net_buoyancy": 300.0
    },
    "pipe_properties": pipe
}

results = lazy_wave.analyze(config)
sag_bend = results["sag_bend"]
hog_bend = results["hog_bend"]

OrcaFlex Model Building

Copyfrom digitalmodel.modules.catenary.orcaflex_model import OrcaFlexModelBuilder

builder = OrcaFlexModelBuilder()
builder.set_line_from_catenary(
    catenary_results=results,
    line_name="Riser1",
    segment_length=5.0
)
builder.add_buoyancy_section(
    start_arc_length=800.0,
    end_arc_length=1200.0,
    buoyancy_od=0.6
)
builder.export_yml("models/riser.yml")

Key Classes

Output Formats

Catenary Shape CSV

Copyarc_length,x,z,tension,curvature,bend_moment
0.0,0.0,100.0,1523456.7,0.000123,1875.4
10.0,9.8,98.5,1518234.5,0.000145,2215.6

Best Practices

1. Consistent units - Use SI units (meters, Newtons)
2. Coordinate system - Z positive upward, origin at seabed
3. Segment resolution - Use small segments near critical points
4. Curvature check - Verify minimum bend radius constraints

Related Skills

• orcaflex-modeling - Run OrcaFlex simulations
• fatigue-analysis - Fatigue at critical locations
• structural-analysis - Stress verification

References

• API RP 2RD: Design of Risers for Floating Production Systems
• DNV-OS-F201: Dynamic Risers