# Orcaflex Modal Analysis Dof Percentage Calculation

> Sub-skill of orcaflex-modal-analysis: DOF Percentage Calculation (+2).

- Skill: `vamseeachanta/orcaflex-modal-analysis-dof-percentage-calculation` (Agent Skill)
- Install (CLI): `npx skillmds@latest add vamseeachanta/orcaflex-modal-analysis-dof-percentage-calculation`
- Raw SKILL.md: https://api.skillmd.com/api/skills/vamseeachanta/orcaflex-modal-analysis-dof-percentage-calculation/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: vamseeachanta (https://skillmd.com/u/vamseeachanta)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/vamseeachanta/orcaflex-modal-analysis-dof-percentage-calculation

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# DOF Percentage Calculation (+2)

## DOF Percentage Calculation


For each mode, the DOF percentage indicates how much of the mode's energy is in each degree of freedom:

```
DOF_percentage = (|max_DOF_value|² / Σ|all_DOF_values|²) × 100
```

## Mode Selection Criteria


A mode is "selected" for a DOF when:
- `DOF_percentage > threshold_percentage`

This filtering helps identify:
- **Heave-dominated modes** (Z threshold)
- **Surge/sway modes** (X/Y threshold)
- **Roll/pitch/yaw modes** (Rotation thresholds)

## Relationship to VIV


Modal frequencies are critical for VIV assessment:

```python
# VIV lock-in check
from digitalmodel.subsea.viv_analysis.viv_analysis import VIVAnalysis

viv = VIVAnalysis()

# Get natural frequency from modal analysis
natural_freq = 1 / mode_period  # Hz

*See sub-skills for full details.*