Troubleshooting

CableDyn is designed to fail closed with a clear message rather than return a quiet wrong answer. This page maps the messages you will actually see — a rejected deck, a solve that will not converge, a combination outside the coupled boundary of OpenFAST (maintained by NLR, the National Laboratory of the Rockies, formerly NREL) — to the reason and the supported path forward. Questions about results and settings are answered in Frequently asked questions.

Exit codes at a glance

Code	Meaning	First thing to check
0	completed; the completion line CableDyn_driver: converged run written to <out_root>.out is on stdout	—
1	the run was refused or its input could not be used: unknown option, wrong argument count, empty or over-long argument, output root equal to the deck, unwritable output directory, unreadable or unparseable deck or auxiliary file, out-of-range value, unsupported feature, or an output file that cannot be opened during the run	the stderr message names the file, line, keyword, or feature — see below
2	an EI = 0 static line or a dynamic step did not converge, a finite-EI static initialisation failed or was rejected, or a result became non-finite. A message starting plausibility guard: means a converged dynamic step produced an element strain beyond maxStrain (default 50 %) — a numerically unstable march, not a physical load. A Windows GNU source build also stops with code 2 when it cannot load its LAPACK library (openblas.dll)	geometry, mesh, time step, and continuation — see Non-convergence; for the plausibility guard, reduce dtM first; for a missing library, see the last section of this page

The complete stream and exit-code contract is in Standalone Windows driver. Error messages are on stderr. If you redirected it away (2>/dev/null), rerun without the redirect.

A run that stops before TMax with no error message and without the closing line CableDyn_driver: ended with exit code <n> was ended from outside the driver, for example by taskkill /F (which leaves exit code 1) or End task; taskkill /IM CableDyn_driver.exe ends every CableDyn run on the computer at once. An interrupt or a fatal fault is reported on stderr with the simulated time reached. See When a run ends early.

Reading an error message

A row-level parse error names the file and line and quotes the offending row:

CableDyn_DeckDriver: deck line 42: column 3 value "500/2" contains "/", ",", ";" or a repeat count "n*"; ... [row: 1 chain 500/2 ...]

Auxiliary files use their own label in place of deck (for example motionFile line 7 or bathymetry file line 3). Validation errors that are not tied to one row name the object instead: a duplicate or undefined id is quoted in the message (duplicate POINT id 4, LINE 2 references undefined POINT id 9).

A deck is rejected (exit 1)

Fail-closed at parse is a feature: it means the deck named something CableDyn will not silently reinterpret. The tables below are grouped by message class.

Command line and files

Message	Cause and fix
unknown option "--x"	only -h/--help and -v/--version (as the first argument) are options; any other argument starting with - is refused before the deck is read.
usage printed on stderr, no other message	the driver needs exactly two arguments: <deck.dat> <out_root>.
argument N is longer than 4096 characters / command-line argument N is empty	shorten the path (run from the case directory and use relative paths) or supply the missing argument.
would overwrite the input deck	the output root is the deck’s own stem, so <out_root>.out or <out_root>.static.out would be the deck. Choose a different root; do not append .out to it.
cannot write output files at "<root>"	the output directory does not exist or is not writable. Create it first; the driver does not create directories.
the name has characters the Windows ANSI code page cannot represent	only a driver built from source with the GNU toolchain gives this: the name is outside the system code page and the volume has no 8.3 short name for it. Use the release CableDyn_driver.exe, which accepts names in any script, or rename the folder.
a file in a folder with accented or non-Latin characters is not found, with an older or self-built executable	the release executables run with UTF-8 as their Windows code page and open such folders (Windows 10 version 1903 or later). An executable built without app/utf8_code_page.manifest uses the system ANSI code page; run it from a folder whose name that code page can spell.
cannot open deck / cannot open motionFile / cannot open bathymetry file / cannot open the WaterKin file / cannot open Syrope settings file / cannot open Syrope OWC table	a referenced file is missing or unreadable. Paths inside a deck are resolved relative to the deck’s directory (the OWC table relative to the Syrope settings file), not to the terminal’s current directory. A # or ! in a path starts a comment and truncates it.
cannot open output file (during the run)	an output file became unwritable after the start-up check (for example, it is open and locked in another program). Close it and rerun.

Records, tokens, and sections

Message	Cause and fix
deck line N: column C value "500/2" contains "/", ",", ";" or a repeat count	a table value that is not one plain number. CableDyn never reads 500/2 as 500, 400,0 as 400, or 2*200 as two values. Write the number with a . decimal point; quote a text value (for example a type name) that must contain such a character. The same rule applies to numeric OPTIONS values (1/20 dtM is rejected as malformed numeric OPTION value) and to motionFile, bathymetry, WaterKin, and Syrope table rows.
deck line N is longer than 512 characters	a record whose text outside a #/!/-- comment does not fit the record buffer. Split a long OUTPUTS list over several rows or move commentary behind #. Long comment lines are accepted. Auxiliary files report the same error with their own label.
unknown deck section "<NAME>"	a record containing --- is always read as a section header. Use one of the header names listed in Deck format reference (.dat), and keep --- out of data rows and descriptions.
LINE TYPES row needs 10 cols ... / POINTS row needs 5 ... or 9 ... / LINES row needs 3 ..., 4 ..., or the stock 7 cols ... / SECTIONS row needs 4 cols	a row with the wrong number of columns. A stray comment without #/! or an unquoted name with a space adds a column.
malformed LINES row: attachment X must be an unquoted point id or rod end (R<N>A, R<N>B)	a LINES attachment is neither a point id nor a rod end. Rod ends can be named directly (R1A, Rod1B); CableDyn creates the end point. A body attachment needs a POINT of type Body<N>; attach the line to that point id.
OUTPUTS channel name "..." is longer than 64 characters	shorten the channel; valid channel names are far shorter than the limit.
unknown OPTION keyword "..."	a typo in an OPTIONS keyword, or a keyword that does not exist (for example staticRelTol: static tolerances are built in; dynamic Newton controls use dynamic_solver). Check the spelling against OPTIONS reference and defaults.
unknown OPTION keyword "2.0" on a current/waves row	text after the terminal waves/current keyword that is not introduced by a spaced - adds tokens and hides the positional form. Write airy 2.0 8.0 0.0 waves - description or move the text behind #.
malformed logical OPTION value / malformed tensile_safety value	use one of the spellings listed in OPTIONS reference and defaults (True/False; warn for tensile_safety).
ICmode is not an option	CableDyn always solves the static equilibrium directly; delete the ICmode row.
a channel like Point2px_raw is rejected	an OUTPUTS channel that does not match a supported form, names an unknown id, or has trailing text. See the exact channel grammar in Output files and channels.

Clock, motion, and environment

Message	Cause and fix
dynamic run requires both dtM and TMax options	the standalone driver needs both or neither. Add the missing one.
OPTIONS TMax must be an integer multiple of dtM	choose TMax = n·dtM exactly (for example dtM = 0.05, TMax = 600).
standalone OPTION current requires dtM and TMax (likewise waves, motionFile, frictionMu, RODS, Rigid6 BODY, Point3 BODY, Connect/Free points, finite-EI section (EI>0))	these features act only in a dynamic march. Add dtM/TMax, or remove the feature for a static calculation. A mixed EI = 0 + finite-EI deck may run static without them. A coupled (caller-driven) deck takes its clock from the host, so current and frictionMu need no dtM there.
OPTION waves requires WtrDpth	waves need a flat depth; a bathymetryFile alone does not satisfy the wave model.
seabed friction is not supported on decks with Connect/Free points, bodies or rods on this route (coupled Rigid6/ROD decks, point decks and the staggered body scheme)	these routes have no seabed friction. Remove frictionMu, or run a standalone body or rod deck on the default monolithic body scheme.
OPTION nModes is not supported for mixed EI=0/finite-EI decks; remove it or set it to 0	a deck that mixes EI = 0 and finite-EI lines writes no modal files. Run the modal analysis on a deck whose lines are all EI = 0 or all finite-EI.
motionFile time is outside the dtM/TMax grid	every row time must be k·dtM for 0 ≤ k ≤ TMax/dtM. Resample the history onto the dtM grid.
motionFile must provide every Coupled/Vessel point at every dtM time (or every eligible prescribed point)	the file is missing at least one (point, time) pair. Every prescribed point needs a row at every grid time, including t = 0 and t = TMax.
motionFile rows must be: time point_id x y z vx vy vz ax ay az	a row has fewer than eleven plain numbers, or a header line is not commented. Comment header lines with #.
motionFile ... which is not Coupled/Vessel / duplicate row for point	the point_id is not a prescribed point, or a (point, time) pair appears twice.
Connect/Free dynamic-point deck does not support motionFile coupling / mixed-deck motionFile is not supported	these routes hold their coupled endpoints. Remove motionFile or separate the model.
bathymetry file must define one complete rectangular grid / grid is incomplete / duplicate x/y entries / needs at least a 2x2 grid / depths must be positive	the x y depth rows must cover every combination of the distinct x and y values exactly once (any order), with at least two of each and positive depths.
OPTIONS WtrDpth and bathymetryFile are mutually exclusive	keep one seabed definition.
Wheeler stretching is undefined: the wave trough reaches the seabed	the wave trough is at or below the seabed (depth + eta <= 0). Reduce the wave height or increase WtrDpth; the model is not valid in that sea state.
WaterKin WaveKinMod 2/SEASTATE is coupled-only	SEASTATE, WaveKinMod 2, and CurrentMod 2 take kinematics from the OpenFAST SeaState field. In the standalone driver use WaveKinMod 0/1 and CurrentMod 0/ 1, or native waves/current rows.
WaterKin WaveKinMod 1 is supported only by the standalone driver	an elevation-history file cannot drive a coupled run or a mixed standalone deck. Put the sea state in SeaState (coupled) or use a single-family standalone deck.
WaterKin WaveKinMod 1 requires ... / WaveKinFile ...	WaveKinMod 1 needs a WaveKinFile of at least four finite time elevation rows starting at t = 0 with increasing times, a positive dtWave, and a positive TMax; it cannot be combined with a waves OPTION or CurrentMod 2.
... BOTH a current OPTION and a WaterKin current (double-counting)	keep either the current row or the WaterKin CurrentMod 1 table.
a WaterKin wave/current combination is rejected	the requested host and file sources cannot be separated by the nodewise fluid sampler without double counting. Use independent sources that Capabilities and route selection lists, or move the complete environment into OpenFAST SeaState.

Model data

Message	Cause and fix
has a non-finite property / POINT has non-finite position or load data / BODY has non-finite data / motionFile contains a non-finite value	a NaN or Inf reached the deck, usually from a generating script. Fix the source value; CableDyn does not substitute defaults.
LINE End A fairlead (NodeA) must not be below End B anchor (NodeB)	End A is the fairlead/upper end. A stock anchor-first row (Fixed NodeA, fairlead NodeB) is swapped automatically; this message means the fairlead point itself lies below the anchor. Check the point coordinates.
LINE End A (NodeA) must be Coupled/Vessel/Body<N> ... / LINE End B (NodeB) must be a Fixed (anchor) point	in a deck without dynamic points every line runs from a fairlead to an anchor. Use Connect/Free points for line-to-line junctions.
finite-EI section (EI>0) requires a dynamic deck with dtM and TMax	a single-family finite-EI deck is solved by the dynamic finite-EI workflow. Add dtM/TMax (TMax = 0 gives the static configuration only).
is net-buoyant (dry mass <= displaced water mass)	an EI = 0 section whose dry mass ≤ displaced mass (a buoyant arch) is outside the EI = 0 route — a lazy-wave arch needs the finite-EI path. Give the buoyant section an EI > 0 line type, or specify it by target submerged weight (the EQUIVALENT BUOYANCY block in Deck format reference (.dat)).
the viscoelastic dynamic stiffness Ed (EA = Es|Ed) must be finite and exceed the static Es	Ed must be strictly greater than Es; equal values make the series spring infinite. For Es|alphaMBL|vbeta both extra values must be positive. Viscoelastic types need EI = 0.
a LINE TYPES BA entry cannot have more bar-separated values than its EA entry	write BA as one value for a plain EA and at most Bs|Bd for a viscoelastic EA.
a Syrope line does not support ... / a Syrope line must be a single section / must be taut at init / has no static output	a Syrope line is one EI = 0 section, taut at initialisation, marched with dtM/TMax, without bathymetryFile, deck current/waves, or host fluid loads (a flat WtrDpth is accepted). Adjust the model accordingly.
Syrope alpha and beta ... must be positive / the Syrope BA column needs two parts / the Syrope settings file needs OWC, WCType, k1, and k2 rows	see the Syrope column rules in Deck format reference (.dat): EA = SYROPE:<file>|alpha|beta with positive alpha/beta, BA = BA_s|BA_d non-negative with a positive sum.
SYROPE IC references undefined LINE id	the SYROPE IC section must come after LINES; also check the line id.
Point3 BODY requires Mass > 0 ... / Point3 BODY currently supports exactly one Body<N> attachment point	a Point3 body needs positive mass, non-negative Vol/CdA/Ca, and exactly one Body<N> point.
Rigid6 BODY requires Mass/Ixx/Iyy/Izz > 0 ... / BODIES row needs 15 cols plus optional Ixx Iyy Izz	a Rigid6 row needs the three trailing inertias (18 columns), all positive.
Rigid6 dynamic deck cannot mix ... / Rod dynamic deck cannot mix ...	each standalone route owns one object family. Split the model or use the combinations listed in Capabilities and route selection.
a ROD may have at most one Rod<N>A point and one Rod<N>B point / Coupled/Vessel ROD requires a motionFile (or a coupled host) / ROD endpoints must define a positive length	remove the duplicate rod-end POINT row (the end points are created automatically when a line names the rod end), supply motionFile rows for both ends of a prescribed rod, and give the rod distinct end coordinates.
FAST.Farm Turbine<J> decks are consumed by the CompMooring=5 aggregate path only	Turbine<J> points use turbine-local coordinates. Run the deck through FAST.Farm, or replace them with Coupled points in global coordinates for a standalone run.
END CONNECTIONS requires a finite-EI line / non-pinned END CONNECTIONS require a finite-EI line with Fixed End B	bending end connections apply only to EI > 0 lines whose End B is an anchor.
a clamped or elastic END CONNECTION on a body or rod needs bodyScheme monolithic / the END CONNECTION direction on a rod end must be parallel to the rod axis	remove staggered bodyScheme; on a rod end give the direction along the rod axis (either sense).

Torsion

Message	Cause and fix
END CONNECTIONS row needs 6 columns ..., or 10 or 11 with the torsion columns	a torsion row is LineID End Stiffness EzX EzY EzZ TorsStiffness NxX NxY NxZ [Pretwist]; see Deck format reference (.dat).
END CONNECTIONS torsional stiffness must be finite and non-negative, Free, or Rigid / torsion reference normal (NxX NxY NxZ) must be non-zero / must not be parallel to the direction Ez	give Free, Rigid or a stiffness in N·m/rad, and a reference normal that is not along Ez.
line <L> is torsionally restrained at both ends: its LINE TYPES row ... must give an explicit GJ > 0	torsion has no EI/1.3 default: use the 14-column LINE TYPES row with GJ (and positive GAs, Irt, Irn) for every section of the line.
torsional END CONNECTIONS ... require a finite-EI line / require a finite-EI line with Fixed End B	torsion is solved on cubic-Hermite lines whose End B is an anchor.
a torsional END CONNECTION on a rod end is not supported / on a body needs a Rigid6 body / torsion is not combined with ATTACHMENTS in this build	outside the torsion scope (Capabilities and route selection). Move End A to a Fixed, Coupled/Vessel point or a Rigid6 body, or represent the modules as a smeared buoyancy section.
torsion is not yet supported in coupled OpenFAST runs / torsion is not yet supported in a deck that mixes EI = 0 and finite-EI lines without a BODY, nor in coupled OpenFAST or FAST.Farm runs	run the torsional line standalone (a mixed deck with a body runs on the multibody route, which supports torsion), or set TorsStiffness Free in every END CONNECTIONS row.
a body holding a line restrained in torsion turns by more than 90 deg in one step even after 6 step halvings	the body turns faster than one step can follow the twist; reduce dtM.
torsion in a dynamic run needs the force-blended generalised-alpha (OPTION alpha_force_blend True) / modal analysis (OPTION nModes) of a line with torsion is not yet supported	remove False alpha_force_blend or nModes from a deck with torsion.
OUTPUT "Torq...": line <L> is not torsionally restrained at both ends ..., so it carries no torque	a Torq/Twist channel needs a line with a torsional restraint at both ends.
motionFile: point <id> has a non-zero roll column, but no line restrained in torsion at both ends ... has its moving (non-Fixed) end there / the roll column of point <id> must be 0 at t = 0 / gives the roll column (12th) on some rows only / the roll column (12th, degrees) must be a finite number	the roll column drives the frame of a torsional line’s moving end, starts from 0 (put a constant twist in Pretwist), and appears on every row of the point or on none (Auxiliary input files).

FAILURE and CONTROL sections

Message	Cause and fix
FAILURE row needs 5 cols / FAILURE row has trailing content	write FailID Point Lines FailTime FailTen with the line list comma-separated and no spaces (1,2).
FAILURE FailIDs must be sequential from 1	number the rows 1, 2, 3, … in deck order.
FAILURE ... lists line L, which is not attached to point P	every listed line must end at the failing point.
FAILURE needs FailTime > 0 or FailTen > 0	a row with both triggers at zero could never fire.
FAILURE at a rod end (R<n>A/R<n>B) is not supported	failures act on POINTS; name the point id (P<n> or an integer).
FAILURE requires a dynamic deck / FAILURE is not supported on finite-EI decks / ... on ROD decks / FAILURE deck does not support motionFile coupling / ... seabed friction	FAILURE runs on the EI = 0 point-system and Rigid6 dynamic routes without rods, motionFile, or frictionMu.
FAILURE on a Rigid6 BODY deck does not support Connect/Free or Point3 body points	a FAILURE deck with Rigid6 bodies runs on the staggered body scheme, which takes the bodies and their lines only; model a clump or buoy on the line as part of a body.
this entry point does not support the CONTROL section	the standalone driver does not consume CONTROL. Line control is an OpenFAST CompMooring = 5 feature for EI = 0 decks; remove the section for a standalone run.
CONTROL row has trailing content / line L is assigned to more than one CONTROL channel	write ChannelID Lines with a comma list without spaces, and assign each line once.

A solve does not converge

An EI = 0 static line that does not converge, or a dynamic step that does not converge after the recovery substeps, ends the run with exit code 2; the .out holds the converged prefix for inspection only. A finite-EI static initialisation failure (finite-EI cable static solve failed or unresolved/kinked finite-EI equilibrium) also ends the run with exit code 2.

The EI = 0 catenary path and the finite-EI static solve are both robust from a trivial seed, but a few geometries are genuinely hard:

• A large grounded touchdown on the EI = 0 path. A long, near-horizontal grounded run can make the linear-Lagrange tangent singular regardless of seed. If the case is a lazy-wave or bending-dominated cable, use the finite-EI path (EI > 0), which is built for it.

• A finite-EI lazy-wave cable at too coarse a mesh. An under-resolved arch or touchdown carries a large element h·κ and can stall the dynamic Newton. The resolution metric flags this; the builder can auto-refine a fragile mesh when the deck opts in (adaptive_mesh True). This remains true when a large net-buoyant mesh first uses coarse-to-fine sequencing: the converged sequenced state is still diagnosed and, when necessary, warm-start refined. Otherwise increase NumSegs on the sag-bend and hang-off sections.

• Several separated finite-EI contact regions. These can be physical: a cable can bridge a bathymetric rise, or a buoyant section can separate two broad grounded heavy sections. CableDyn records the island count but does not reject that topology. Adaptive refinement is requested only when contact classification toggles over one interior node (an isolated contact node or isolated suspended gap), which is a mesh-scale signal; refine the local sections if that signal remains active.

• A residual-converged folded branch. CableDyn checks the element rotation measure after every finite-EI sequence attempt, every final deck-built equilibrium, and the public automatic-mesh route. max(h*kappa) > 0.7 is rejected by name even if Newton’s residual is small. This is a mesh/branch safety failure, not permission to relax the tolerance. Increase resolution in the reported high-curvature section and inspect the static profile. The check samples element interiors adaptively, so a cubic-element fold cannot hide between output nodes.

• Odd, prime, or section-wise nonuniform meshes. These are supported; do not change NumSegs merely to make the total divisible by two. The nested hierarchy retains physical section interfaces and interpolates at the true cumulative rest-length coordinate. Its suspended-span bending-scale preflight checks the actual longest proposed coarse element, so a sparse long section is not over-coarsened merely because the deck also contains many short elements. Flat-bed installed lines with an already supported anchor retain their grounded-tail branch homotopy and are still accepted only after exact-mesh residual and kink checks.

• A very slack cable on a frictionless flat bed. If its rest length exceeds the vertical-plus- horizontal L-shaped path between the endpoints, a smooth single-touchdown equilibrium may not exist: the surplus must fold or form another contact region. CableDyn rejects a resulting element-localized wad through the curvature safety check. This is not fixed by relaxing Newton tolerances; revise the physical support/contact model or geometry.

• A twisted finite-EI line. torsion continuation stalled at Phi = ... (target ...) reports the imposed twist the static ramp reached: beyond it the line has no nearby static equilibrium on the path, typically because a loop is forming (hockling), which needs a dynamic analysis and is not resolved as self-contact. finite-EI torsion static solve ended on an unstable equilibrium means the descent from a buckled (unstable) twisted state did not find a stable one. the twist moved more than pi/2 from its committed value in one step stops a dynamic step that would change the twist by more than a quarter turn (the unwrapping of the twist cannot be trusted beyond it): reduce dtM or slow the imposed roll. tangent turns by more than 120 degrees names an element or node pair where the twist of the centreline is no longer reliable: refine the mesh there.

• A cold start at full load. The static solve continues the load in stages; if you have hand-tuned a case into a bad basin, remove the tuning and let the default continuation run from the catenary/arch seed.

If a dynamic step fails after a good static IC, the usual cause is a time step too large for a transient event (a snap) — but note the implicit integrator’s whole point is large steps, so first confirm the static IC itself is smooth (plot the <out_root>.static.out curvature). The failure message reports the simulated interval; recovery_max_substeps raises the internal subdivision ceiling, and dynamic_solver sets the dynamic Newton tolerance and iteration budget (see OPTIONS reference and defaults). Qualify any change against a smaller dtM.

Warnings and notes that do not stop a run

Note: line <L> is torsionally restrained at one end only; ... no torsion is solved	with the other end free to twist the line carries no torque, so the torsion columns of the restrained end have no effect. Restrain both ends to solve torsion.
Note: line <L>: torsion solved, imposed twist ... deg, torque ... N m (<n> twist stage(s), <m> buckling descent(s))	the static twist stage of a torsional line. A non-zero descent count means the straight or untwisted branch was unstable at the imposed twist and the solve moved to a buckled shape; check the shape and the Twist<L> channel.
Message	Cause and fix
WARNING: line type ... sinks ... m into the seabed ...; kBot is soft for this line	a grounded run of this type would sink deeper than its own diameter into the penalty seabed. Raise kBot; the default 1.0e5 embeds a heavy chain by about half its diameter, which is normal.
WARNING: LINE ... hangs ... m below its Fixed anchor and the deck has no seabed	the deck has no WtrDpth or bathymetryFile, so a slack mooring hangs through the missing seabed. This is typical of an OpenFAST MooringFile, which takes the depth from the host; add WtrDpth for a standalone run.
Note: motionFile point ... starts moving at ... m/s	the lines start at rest, so an end that starts at speed sends an axial shock down the line and can put its upper part into compression for several steps. A harmonic started at t = 0 begins at its peak velocity. Start the motion from rest or ramp its amplitude in over one or two periods, as examples/data/lozon/generate_gomex80_heave.py does.
Note: line ...: the static layout carries the grounded run ... m past its anchor, where it folds back (a hairpin) ...	a very strong current on a frictionless seabed has pushed the line past its anchor, and it folds back to it (see Theory). The layout is a valid, stable equilibrium of the deck as written, but not the usual one. If the real seabed holds the line, declare frictionMu; otherwise check the line length and the current, and inspect <out_root>.static.out before using the layout.
Note: line ...: the equilibrium in the current is held in the vertical plane of the line; it is unstable out of that plane ...	in a current along the plane of the line the static state is a planar equilibrium that a lateral disturbance would leave (the line is held in the plane only by the symmetry), and no out-of-plane equilibrium was found. The state is valid in the plane; a cross-flow component or seabed friction (frictionMu) gives the line a stable layout.
Note: line ...: a nodal tangent turned up to ... deg in one step	the time-step audit of a finite-EI line: above 0.25° per step (0.1° with False alpha_force_blend) the mean tension can err by about 1 %. Reduce dtM.
Note: line ...: elements as short as ... are below sqrt(EI/EA)	the finite-EI deck mesh is finer than the axial-bending length \(\sqrt{EI/EA}\): the axial stiffness of each element swamps its bending stiffness and the static Newton system loses the precision to converge. An 80 m lazy wave (6.5 mm limit) solves at 8 mm elements and not at 4 to 6 mm, where the solve stops within seconds and names the mesh. Coarsen NumSegs to at least the length the note gives.
Note: line ... mesh too coarse for its bends	the element-mean axial force of a finite-EI line, averaged with its neighbours, is compressive, and the pointwise resultant oscillates well beyond it. Refine NumSegs in the reported region, or set tensile_safety True to reject the state. A pointwise dip at a seabed touchdown with tensile neighbouring elements is not reported.
curvature near a hang-off changes with dtM or the mesh	end curvature is a boundary-layer quantity. Run a dtM study (halve it until the value changes by less than a few percent), grade the mesh toward the end, and report the value 1–2 m from a pinned end, not at the pinned node (see Modelling workflow, step 5).

An OpenFAST CompMooring = 5 run fails at init

The module covers the scoped MoorDyn-F coupled surface and fails closed outside it. If init aborts with a CableDyn fatal error, check whether the deck uses one of these combinations:

Not supported on the coupled route	Use instead
active ServoDyn control (CONTROL) on a deck with a finite-EI cable, or in FAST.Farm	EI = 0 line control is supported in a single-turbine model; for a controlled cable, use stock MoorDyn (CompMooring = 3) in the same binary
deck waves/wavetrain OPTIONS, and a deck current on a deck with finite-EI cables, Rigid6 bodies or rods, in FAST.Farm, or with a SeaState that carries waves or current	put the sea state and current in SeaState, or a current table in a WaterKin file (CurrentMod 1); a steady deck current is kept on a single-turbine, pure EI = 0 deck in a SeaState without waves or current
a finite-EI cable in the same deck as Rigid6 bodies, rods, or Connect/Free points	model the cable and the body/point system in separate decks or use the supported combinations in Capabilities and route selection
OpenFAST linearisation with a platform-relative cable END CONNECTIONS row (formal OpenFAST linearization with a platform-relative cable end connection is not supported) or with a CONTROL section	linearise a pinned-hang-off, uncontrolled variant of the deck; time-domain runs support both
a Rigid end-connection direction reversed by exactly 180 degrees in one host update	drive the platform through intermediate orientations
VIV (compVIV)	use a solver with a separately validated VIV model
a host/file fluid combination named as inseparable	select host wave/current and file wave/current independently as documented, or place the whole field in SeaState
a Point3 restoring model beyond buoyancy and supported fluid loads	represent the restoring physics with supported line/body terms or use stock MoorDyn

Finite-EI rotational end coupling is supported in the time domain on the coupled route: an END CONNECTIONS direction at a coupled hang-off rotates with the OpenFAST platform orientation, the mesh angular velocity and acceleration enter the implicit residual, and the connection moment is returned to OpenFAST on the load mesh (see OpenFAST with CompMooring = 5). In the standalone driver an end-connection direction stays fixed in global axes on a Fixed or Coupled point driven by a motionFile, and turns with the vessel under vesselMotion or vesselRAO.

Everything CableDyn does support end-to-end — coupled time-domain analysis, PtfmInit, NumCrctn > 0, SeaState kinematics, checkpoint-restart, linearisation, rigid bodies/rods, and Mod_SharedMooring = 5 — is listed in Capabilities and route selection.

The standalone binary will not launch (Windows)

Use the release CableDyn_driver.exe or CableDyn-enabled openfast.exe. Those two non-OpenMP x64 files are statically linked and require no adjacent compiler, BLAS, OpenMP, or C/C++ runtime DLL. A locally built GNU/OpenMP executable may still require its selected toolchain libraries. A GNU build loads openblas.dll from its own directory when it starts; if the library is missing, the driver stops with exit status 2 and a message naming the library, each location tried, and the Windows load error. Keep openblas.dll next to the executable (cmake --install stages it) or run from the activated environment. A missing DISCON.dll is different: the OpenFAST model explicitly requested a ServoDyn controller, so copy that model-specific controller with the model or disable it. See Installation (standalone binaries).

If your issue is not here, see Frequently asked questions; the Deck format reference (.dat) row for the feature is the authoritative statement of what is supported, and CableDyn verification and validation records exactly which cases are validated.