# Catenary Riser

> 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.

- Skill: `vamseeachanta/catenary-riser-2` (Agent Skill)
- Install (CLI): `npx skillmds@latest add vamseeachanta/catenary-riser-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/vamseeachanta/catenary-riser-2/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: vamseeachanta (https://skillmd.com/u/vamseeachanta)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/vamseeachanta/catenary-riser-2

---


# Catenary Riser

## 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)


<!-- ace:known-missing: digitalmodel.subsea.catenary.orcaflex_model, digitalmodel.subsea.catenary.orcaflex_model.OrcaFlexModelBuilder, digitalmodel.subsea.catenary_riser.LazyWaveAnalyzer -->

## Python API

### Simple Catenary Equation

```python
from digitalmodel.marine_ops.marine_analysis.catenary import CatenarySolver, CatenaryInput
import numpy as np

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

horizontal_tension = catenary.solve(
    top_end=top_end,

*See sub-skills for full details.*
### Catenary Riser Analysis

> **`CatenaryRiser` does not exist.** Build the configuration and call
> `CatenarySolver` directly. Do **not** reach for
> `digitalmodel.subsea.catenary_riser.LazyWaveAnalyzer`: it is **quarantined**
> (`tests/subsea/catenary_riser/test_lazy_wave_quarantine.py`) because it
> returned hardcoded fractions of water depth with buoyancy having no effect,
> and it now raises `NotImplementedError`.

```python
from digitalmodel.marine_ops.marine_analysis.catenary import CatenarySolver
from digitalmodel.infrastructure.base_solvers.marine.pipe_properties import PipeProperties

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

*See sub-skills for full details.*
### Lazy Wave Catenary

> Verified against this solver in an end-to-end engagement (aceengineer-agents
> `examples/lazy-wave-verification/`). Note `results.vertical_force` is
> **defective** — it returns `Fv + Fh`; the correct vertical component is
> `w · S_hangoff` (digitalmodel#2044).

```python
from digitalmodel.marine_ops.marine_analysis.catenary import (
    LazyWaveSolver, LazyWaveConfiguration, derive_hangoff_bend_radius
)

lazy_wave = LazyWaveSolver()
config = {
    "water_depth": 1500.0,
    "hang_off_angle": 8.0,
    "buoyancy_section": {
        "start_length": 800.0,
        "end_length": 1200.0,

*See sub-skills for full details.*
### OrcaFlex Model Building

> **`OrcaFlexModelBuilder` does not exist anywhere in `digitalmodel`.** The
> snippet below documents an intended capability that was never built. Treat it
> as a specification, not as runnable code, and build the OrcaFlex model through
> `digitalmodel.solvers.orcaflex` instead.

```python
# NOT RUNNABLE -- OrcaFlexModelBuilder does not exist. Specification only.
from digitalmodel.subsea.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(

*See sub-skills for full details.*

## Key Classes

| Class | Purpose |
|-------|---------|
| `CatenaryEquation` | Mathematical catenary solver |
| `CatenaryRiser` | Main analysis orchestrator |
| `LazyWaveCatenary` | Dynamic catenary with buoyancy |
| `PipeProperties` | Material and geometric properties |
| `OrcaFlexModelBuilder` | Model export to OrcaFlex |

## Related Skills

- [orcaflex/modeling](../orcaflex/modeling/SKILL.md) - Run OrcaFlex simulations
- [fatigue-analysis](../fatigue-analysis/SKILL.md) - Fatigue at critical locations
- [structural-analysis](../structural-analysis/SKILL.md) - Stress verification

## References

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

## Sub-Skills

- [Best Practices](best-practices/SKILL.md)

## Sub-Skills

- [Version Metadata](version-metadata/SKILL.md)
- [[1.0.0] - 2026-01-07](100-2026-01-07/SKILL.md)
- [1. Simple Catenary Analysis (+2)](1-simple-catenary-analysis/SKILL.md)
- [Catenary Shape CSV](catenary-shape-csv/SKILL.md)