Methodology
This analysis implements DNV-RP-F105 simplified VIV screening
for pipeline and jumper freespans. The methodology evaluates whether
vortex-induced vibrations will develop under steady current loading,
using the reduced velocity parameter VR = V / (fn × D).
Screening Steps
- Natural frequency — beam-on-elastic-foundation model
with pinned-pinned boundary conditions (conservative).
fn = Cn/(2π) × √(EI / meffL4)
- Reduced velocity — VR = Vcurrent / (fn × D)
- VIV onset check — in-line onset at VR = 1.0,
cross-flow onset at VR = 3.0, lock-in range 4.0–8.0
- Gap ratio correction — seabed proximity (e/D < 1) delays VIV onset
- Response amplitude — simplified A/D estimation for screening
Parameter Matrix
- Pipelines: 8", 12", 16" × 8 spans (10–80 m)
× 5 currents (0.2–1.0 m/s) × 4 gap ratios = 480 cases
- Jumpers: 8" rigid × 8 spans (5–40 m)
× 5 currents × 5 gap ratios (incl. mid-water) = 200 cases
Screening Criteria
- PASS — no VIV expected (VR < 1.0)
- INLINE_ONLY — in-line VIV only
(1.0 ≤ VR < 3.0), typically acceptable
- FAIL_CF — cross-flow VIV onset
(VR ≥ 3.0), detailed analysis needed
- FAIL_LOCKIN — lock-in regime
(4.0 ≤ VR ≤ 8.0), critical condition
Applicable Codes & Standards
- DNV-RP-F105 (2017) — Free Spanning Pipelines
- DNV-RP-C205 (2010) — Environmental Conditions and Loads
- DNV-OS-F101 (2013) — Submarine Pipeline Systems
Screening Results Summary
Pass rate includes PASS + INLINE_ONLY (acceptable for most applications).
| Type |
Size |
Cases |
PASS |
INLINE_ONLY |
FAIL_CF |
FAIL_LOCKIN |
Acceptable % |
| Pipeline |
8in |
160 |
4 |
17 |
131 |
8 |
13% |
| Pipeline |
12in |
160 |
12 |
20 |
112 |
16 |
20% |
| Pipeline |
16in |
160 |
21 |
17 |
102 |
20 |
24% |
| Jumper |
8in-jumper |
200 |
31 |
35 |
99 |
35 |
33% |
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Assumptions & Limitations
- Pinned-pinned boundary conditions (conservative — actual supports provide partial fixity)
- Steady uniform current perpendicular to pipe axis (worst case orientation)
- No wave-induced loading considered (current-only screening)
- Effective axial force = 0 (no temperature/pressure-induced axial load data)
- Added mass coefficient Ca = 1.0 (potential flow theory)
- Content density = 800 kg/m3 (oil-filled, conservative for empty pipe)
- Coating thickness from pipe catalog (3LPP or FBE)
- Thinnest available wall thickness used per pipe size (worst case for VIV)
- No soil-pipe interaction stiffness modelled (free span only)
- Single-mode response only (higher modes may be excited at very high V_R)
Chart 1: Natural Frequency vs Span Length
Log-scale frequency showing how longer spans reduce f_n. Jumper's thicker wall gives higher frequency at same OD.
Chart 2: VIV Onset Screening Map
Span-current screening at e/D = 1.0. Green = safe, yellow = inline only, orange/red = VIV concern.
Chart 3: Max Allowable Span Heatmap
Maximum freespan before cross-flow VIV onset at e/D = 1.0.
Chart 4: Pass/Fail Screening Matrix
Full parametric screening results for all pipeline sizes at e/D = 1.0.
Chart 5: Jumper vs Pipeline Comparison
Allowable current envelope: 8in pipeline (Sch 40) vs 8in jumper (Sch 120). Thicker jumper wall extends safe operating envelope.