viv-analysis

name	viv-analysis
description	Assess vortex-induced vibration (VIV) for risers and tubular members with natural frequency and safety factor calculations. Use for VIV susceptibility analysis, natural frequency calculation, vortex shedding assessment, and tubular member fatigue from VIV.
type	reference
updated	2026-01-07
capabilities	[]
requires	[]
tags	[]
scripts_exempt	true
category	engineering
version	1.0.0

Viv Analysis

When to Use

• VIV analysis for risers and pipelines
• Pipeline free-span VIV screening and fatigue prechecks
• Natural frequency calculation for tubular members
• Vortex shedding frequency analysis
• VIV fatigue damage assessment
• Tubular member VIV screening
• Safety factor evaluation against VIV criteria
• Pressure wall prechecks when VIV span inputs depend on pipe wall/section properties

Prerequisites

• Python environment with digitalmodel package installed
• Member geometry and material properties
• Current velocity profiles
• For risers: tension distribution along length

Python API

Natural Frequency Calculation

from digitalmodel.subsea.viv_analysis.viv_analysis import VIVAnalysis
from digitalmodel.subsea.viv_analysis.viv_tubular_members import VIVTubularMembers

# Initialize analysis
viv = VIVAnalysis()

# Define member properties
member = {
    "length": 50.0,

*See sub-skills for full details.*
### Vortex Shedding Analysis

```python
# Vortex shedding frequency
diameter = 0.5  # meters
current_velocity = 1.5  # m/s
strouhal = 0.2

shedding_freq = viv.vortex_shedding_frequency(
    diameter=diameter,
    velocity=current_velocity,
    strouhal_number=strouhal

*See sub-skills for full details.*
### Tubular Member Analysis

```python
from digitalmodel.subsea.viv_analysis.viv_tubular_members import VIVTubularMembers

# Initialize tubular member analysis
tubular = VIVTubularMembers()

# Define member
member_props = {
    "name": "Brace1",
    "outer_diameter": 0.324,

*See sub-skills  full details.*


```python
 digitalmodel.subsea.viv_analysis.viv_fatigue  VIVFatigue


viv_fatigue = VIVFatigue()


stress_range = viv_fatigue.calculate_stress_range(
    amplitude=,  
    diameter=,

*See sub-skills  full details.*



For subsea pipeline span work, treat VIV screening  a coupled structural/fatigue workflow rather than a standalone vortex-shedding calculation:

 Establish pipe section properties  the actual design basis: OD, nominal WT, corrosion allowance, mill tolerance, grade/SMYS, weld factor, temperature factor,  code/design factor.
 Run a pressure-wall sanity check before relying on the section  span/fatigue calculations. When using `digitalmodel`, prefer the pipe-capacity implementation under `src/digitalmodel/structural/pipe_capacity/`  document the equation branch used.
 Use minimum/corroded wall  span stress  fatigue section properties unless the governing code  project basis specifies another convention.
 Then evaluate span natural frequencies, reduced velocity, lock- susceptibility, stress , fatigue damage,  acceptance criteria under DNV-RP-F105 / DNV-ST-F101  project-specific rules.
 Do  present pressure containment  final wall adequacy; collapse, propagation buckling, local buckling, installation, hydrotest, thermal/strain, on-bottom stability,  VIV/free-span fatigue may still govern.

See `references/pipeline-span-pressure-wall-precheck.md`  the session-derived digitalmodel pressure-wall pattern    /  psi example.



| Class | Purpose |
|-------|---------|
| `VIVAnalysis` | Main VIV analysis router |
| `VIVTubularMembers` | Tubular member assessment |
| `VIVAnalysisComponents` | Component-level analysis |
| `VIVFatigue` | VIV-induced fatigue damage |



- [catenary-riser](../catenary-riser/SKILL.md) - Riser configuration
- [fatigue-analysis](../fatigue-analysis/SKILL.md) - VIV fatigue damage
- [structural-analysis](../structural-analysis/SKILL.md) - Stress verification



- DNV-RP-C205: Environmental Conditions  Environmental Loads
- DNV-RP-F105: Free Spanning Pipelines
- Blevins, R.D.: Flow-Induced Vibration



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



- [Version Metadata](version-metadata/SKILL.md)
- [[] - -01-07](--01-07/SKILL.md)
- [ Natural Frequency Analysis (+)](-natural-frequency-analysis/SKILL.md)
- [Strouhal Number (+)](strouhal-number/SKILL.md)
- [Complete VIV Screening Workflow](complete-viv-screening-workflow/SKILL.md)
- [Natural Frequencies JSON (+)](natural-frequencies-json/SKILL.md)
- [Design Code References](design-code-references/SKILL.md)