What is Skalnav?
Skalnav is the verification and decision platform for thin-walled structures — mechanistic buckling knockdown factors, curated experimental evidence, and audit-ready reports in one place.
Shell buckling design still runs on 1960s assumptions.
Most structural teams face the same trade-off: accept blanket empirical factors whose margin on their particular shell is unknown, or run expensive nonlinear FE campaigns for every design iteration. Neither approach gives you full visibility into the margin you're working with.
Empirical knockdown factors
NASA SP-8007 ties the knockdown factor to R/t alone — independent of length, imperfection amplitude and fabrication quality. It is a design curve drawn under most of the 1930s–1960s test data, and some of those tests fall below it. Depending on build quality, it can be conservative or optimistic for your shell.
Expensive nonlinear workflows
Running GNIA/GMNIA analyses for every candidate geometry is thorough but slow. Weeks per iteration, high FE expertise required, limited parameter exploration. The design space stays narrow because exploration is costly.
Opaque design margins
When different standards give different allowables for the same shell, which one is correct? Without a transparent, physics-based reference, teams default to the most conservative answer. How much margin that leaves stays invisible.
From fixed empirical factors to mechanistic, imperfection-sensitive predictions.
Skalnav computes knockdown factors as a function of geometry (Batdorf Z) and imperfection amplitude (w/t). The result is a transparent, traceable design basis that works across standards. Where buckling sizes the wall, Skalnav uses a knockdown for your own shell rather than a single empirical curve such as NASA SP-8007's. If that calls for a thicker wall, Skalnav shows it; if it allows a thinner wall, that means less mass, and on a launcher, structural mass trades against payload.
Traditional approach
- Single empirical KDF per geometry class
- Imperfection sensitivity ignored or assumed
- One standard at a time, manual comparison
- Nonlinear FE required for margin visibility
- Usually conservative, sometimes not, and never says by how much
- Days to weeks per design iteration
With Skalnav
- KDF varies with geometry, imperfection, and fabrication class
- Imperfection sensitivity is a parameter, not an assumption
- 9 standards computed simultaneously, side by side
- Analytical pre-design narrows the FE campaign before it starts
- The gap between methods is quantified and traceable
- Seconds per load case, full parameter exploration
“Structured chaos: redefining the design of buckling-critical cylindrical shells.”
Proceedings of the Royal Society A, 481(2321), 2025.
From geometry to audit-ready proof — in four steps.
Define
Enter geometry, load case and material. Cylinder, cone, sphere or torispherical head.
Evaluate
Get the knockdown factor with its mechanistic basis: regime, imperfection sensitivity, Basis A/B — in seconds.
Compare
Check your result against nine design codes side by side, from NASA SP-8007 to EN 1993-1-6.
Document
Export a verification report with the full experimental evidence trail behind every number.
Scope built for real engineering decisions.
Every feature exists because an engineer needed it to close a design trade or defend a result in a design review. Nothing is decorative.
Multi-Standard Comparison
NASA SP-8007, SP-8019, SP-8032, Eurocode 2007 & 2025, DNV RP-C202, ECSS, PD 5500, GOST 34233, and MDC — computed simultaneously on the same geometry and load case. Results side by side. No re-entry, no separate models.
Sizing & Back-Solve
Define a target load. Get the minimum compliant wall thickness across all applicable standards. Integrated with standard sheet thickness catalogues. Answers the question “how thin can I go?” in seconds.
Shell Optimizer
Minimum-mass design of tori-sphere heads under external pressure. Searches wall thickness, crown and knuckle radius against your target pressure — every candidate rated through the full MDC chain, imperfection knockdown included.
Imperfection Sensitivity
Sweep w/t from 0 to 8 for cylinders and cones, and from 0 to 2 for spherical shells, to see how your design responds to manufacturing variability. Identify the threshold where safety margin erodes — before it becomes a test failure or a redesign.
Composite & Sandwich Shells
Classical Laminate Theory with full ABD matrix computation. Carbon, aramid, glass presets. Arbitrary stacking sequences. Smeared-thickness conversion for shell buckling. Anisotropy robustness assessment included.
Plasticity & Combined Loading
Automatic regime detection across elastic, transition, and plastic domains. Patte d’éléphant correction for combined stress states. 20+ load cases including axial, bending, torsion, external and internal pressure, and all relevant combinations.
Validation Hub
1,000+ curated experimental records. Every prediction can be compared against physical test data from published literature. Filter by campaign, geometry, material, failure mode. Discrepancies are visible, not hidden.
Audit-Ready Reports
PDF, CSV, and JSON export (HTML on the roadmap). Full traceability: inputs, intermediate values, charts, applicable standard, statistical basis, engine version, and design verdict. Structured for inclusion in design review and certification packages — formal review, acceptance, and approval remain with you and your certifying authority.
The building blocks an engineer actually uses.
Each capability is exposed as an interactive workflow — not a checkbox. Click through the tabs to see what the tool does when you open it.
See the shells in your neighbourhood that buckled below prediction.
For every MDC analysis, the Hub locates your design point within the 1,000+ curated collapse-test database and flags any nearby experiment that failed below the standards prediction. A non-conservative neighbour is information you cannot get anywhere else — a direct warning to revisit your margins before the design review, not after.
Read the other way, a design surrounded by well-characterised, conservative tests is a documented confidence argument for your review package: the physical record in your parameter neighbourhood, with similarity scores and measured buckling loads.
Whether that evidence supports any given approval remains the decision of the responsible authority — the Hub is supporting evidence, not a substitute for qualification testing. A single query still replaces days of literature search and gives your review package traceable, cited experimental references.
- Spatial query: where your design sits in Z / R/t / K / w/t parameter space
- Nearest-neighbour ranking with similarity scores and measured buckling loads
- Flagging of non-conservative neighbours (experiments below standards predictions)
- Direct citations to original test campaigns for inclusion in certification packages
- Full CSV/JSON export of matching records or the complete database
Know your imperfection before you measure it.
In early design, scan data for your shell does not yet exist — but Eurocode, ECSS, and DNV all require an imperfection amplitude. The Guide closes this gap: a statistically-backed w/t estimate from 172 measured shells covering lab-scale specimens through full-scale aerospace hardware (1970–2024).
Outputs include 90% B-Basis and 95% envelope, split by specimen class, with traceable citations to the original measurement campaigns. Use it to enter a defensible imperfection amplitude before the prototype is built. Provides the imperfection assumptions used in Level 1 analyses, where measured data is not yet available.
- w/t estimate for your R/t and manufacturing class
- 90% B-Basis (regulated design) and 95% envelope (worst-case)
- Power-law and linear fits with log R/t diagnostics
- Split between lab-scale (149) and full-scale aerospace (23) subsets
- Nearby-shell statistics within ±20% R/t
- Traceable citations to original measurement campaigns
Decide what to measure — before you measure.
The Explorer shows where your shell sits in the regime map and how it moves as parameters change. R/t, L/R, imperfection amplitude, yield stress, and load combination — each slider updates the regime band and the knockdown curve in real time.
Step 1 — Imperfection sensitivity. A perfect shell (w/t = 0) sits in Regime 3 across nearly all geometries — local buckling and material yielding dominate. As imperfection amplitude grows, Regime 1 (imperfection-dominated) and Regime 2 (transition) emerge in the lower-Z range, while higher-Z geometries remain comparatively stable. The slider sweep tells you whether your design crosses into a sensitive regime as imperfections rise — and at what amplitude the crossing happens. This sets a practical threshold for fabrication tolerance.
Step 2 — Plasticity penalty. Plasticity does not affect all regimes equally. Regime 1 shells lose more capacity to yielding than Regime 3 shells. The Explorer makes this asymmetry visible in the same view, so the trade-off between regime and material strength is one decision, not several disconnected analyses.
Why this matters in design. A shell deep in Regime 3 with bounded imperfection amplitude is a Level 0 case — the analytical Skalnav result is sufficient. A shell crossing into Regime 1 or 2 is imperfection-driven; either physical measurement (Level 2) or worst-case envelope assumptions (Level 0) are needed. A shell in an unfavourable regime under any reasonable amplitude is a Level 3 candidate.
If your design lands in an unfavourable regime, the Explorer also shows the geometry levers that would shift it: a longer unsupported length raises Z, improving fabrication tolerance lowers w/t — both push toward Regime 3. Ring stiffeners go the opposite direction by lowering effective Z (shortening the unsupported field), which can be useful for local mode shaping or manufacturing constraints, but trades regime favourability for those gains. The Explorer quantifies the trade-off rather than guessing at it.
- Current regime at a glance, across all active parameters
- Live regime transitions as sliders move
- Comparison against the perfect-shell limit
- Geometry levers (length, fabrication quality, stiffeners) and their regime-shift effect
- Whether the design is a Level 0, Level 1, Level 2, or Level 3 candidate
See which standard governs — and how far the others sit from it.
Side-by-side allowable stress for NASA SP-8007, Eurocode 1993-1-6 (2007 and 2025), DNV RP-C202, ECSS-E-HB-32-24A, and MDC-B where each method supports the selected geometry and load case. Governing case is flagged. The spread between the most and the least conservative answer is shown next to the physics-based one.
Report exports identify the selected method, edition, inputs, and calculated results.
Quantify the margin your structures really have.
Size each wall with a knockdown for its own shell, with full traceability. Start in the free Preview mode — no commitment, no credit card.
Read the publication — Proc. R. Soc. A, 2025