Mesh-based nonlinear Froude-Krylov and hydrostatic load calculation in HydroDyn#3336
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luwang00 wants to merge 16 commits into
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Mesh-based nonlinear Froude-Krylov and hydrostatic load calculation in HydroDyn#3336luwang00 wants to merge 16 commits into
luwang00 wants to merge 16 commits into
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…ostatic load calculation in HydroDyn
…static forces and moments
…ll bodies if NBodyMod=1
…Krylov and hydrostatic load model Also fixed a potential bug when NBodyMod=1 and NBody>1. In this case, PotFile and WAMITULEN only have one entry each for all bodies instead of NBody entries. Updated r-test pointer.
…Krylov and hydrostatic option
jjonkman
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This is a great addition to HydroDyn; thanks, Lu! See a few comments on the documentation below.
…ns on the nonlinear Froude-Krylov and hydrostatic load model
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Thanks for addressing my review comments!
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Pull request overview
This PR introduces a new mesh-based nonlinear Froude–Krylov + hydrostatic pressure-integration capability for potential-flow bodies in HydroDyn, including new HydroDyn inputs (FKMod, GeoFile), updated WAMIT file handling (.3sc vs .3), new output channels, documentation updates, and a new regression test.
Changes:
- Add a new
NonlinearFKmodule (STL geometry ingestion + waterline clipping + pressure integration) and wire it into HydroDyn/WAMIT initialization and output mapping. - Extend HydroDyn input parsing + openfast_io reader/writer to support
FKModandGeoFile, and adjust WAMIT excitation file selection (.3vs.3sc) accordingly. - Update docs and reg-tests to cover the new model and outputs.
Reviewed changes
Copilot reviewed 21 out of 23 changed files in this pull request and generated 8 comments.
Show a summary per file
| File | Description |
|---|---|
| reg_tests/CTestList.cmake | Adds a new HydroDyn regression test entry for nonlinear FK/hydrostatics. |
| openfast_io/openfast_io/FAST_writer.py | Writes new FKMod/GeoFile inputs and updates PotFile description for .3sc. |
| openfast_io/openfast_io/FAST_reader.py | Reads FKMod/GeoFile and adjusts PotFile/WAMITULEN parsing for NBodyMod==1. |
| modules/hydrodyn/src/WAMIT2.txt | Adds NonlinearFK registry dependency and FKMod parameter plumbing. |
| modules/hydrodyn/src/WAMIT2_Types.f90 | Adds FKMod to WAMIT2 parameter type + copy/pack/unpack support. |
| modules/hydrodyn/src/WAMIT.txt | Adds NonlinearFK registry dependency and FKMod into WAMIT types. |
| modules/hydrodyn/src/WAMIT.f90 | Selects .3 vs .3sc based on FKMod and disables .hst usage when nonlinear FK is enabled. |
| modules/hydrodyn/src/WAMIT_Types.f90 | Adds FKMod to WAMIT init/params + copy/pack/unpack support. |
| modules/hydrodyn/src/NonlinearFK.txt | New registry describing geometry/body types and init/misc data. |
| modules/hydrodyn/src/NonlinearFK.f90 | New implementation for STL parsing, clipping, and pressure integration. |
| modules/hydrodyn/src/NonlinearFK_Types.f90 | Generated types for the new NonlinearFK module. |
| modules/hydrodyn/src/HydroDyn.txt | Wires NonlinearFK types into HydroDyn registry/types. |
| modules/hydrodyn/src/HydroDyn.f90 | Initializes and calls NonlinearFK, skips WAMIT2 for FK bodies, and maps new outputs. |
| modules/hydrodyn/src/HydroDyn_Types.f90 | Adds FKMod/GeoFile and NonlinearFK init/param/misc fields to HydroDyn types. |
| modules/hydrodyn/src/HydroDyn_Input.f90 | Parses/validates FKMod/GeoFile and enforces incompatibilities (e.g., NAddDOF>0). |
| modules/hydrodyn/CMakeLists.txt | Adds NonlinearFK sources and type generation. |
| docs/source/user/hydrodyn/output_files.rst | Documents summary-file behavior for mesh-based buoyancy/volume reporting. |
| docs/source/user/hydrodyn/input_files.rst | Documents FKMod/GeoFile, .3sc requirements, and behavior changes. |
| docs/source/user/hydrodyn/appendix.rst | Updates example inputs and output-channel appendix entries. |
| docs/source/user/api_change.rst | Records new HydroDyn inputs in the API change log. |
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| USE HydroDyn_Input | ||
| USE HydroDyn_Output | ||
| USE YawOffset | ||
| USE NonlinearFK | ||
|
|
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| call AllocAry( p%FKMod , p%NBody, 'p%FKMod' , ErrStat2, ErrMsg2 ); CALL SetErrStat( ErrStat2, ErrMsg2, ErrStat, ErrMsg, RoutineName) | ||
| p%FKMod = InitInp%FKMod | ||
| if (all(p%FKMod==FKMod_full)) then | ||
| dot3ext = '.3sc' | ||
| else if (all(p%FKMod==FKMod_none)) then | ||
| dot3ext = '.3' | ||
| else | ||
| ErrStat = ErrID_Fatal | ||
| ErrMsg = RoutineName//": When simulating multiple potential-flow bodies with NBodyMod=1, all bodies must have the same FKMod. " |
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| IF ( InputFileData%PotMod == 1 ) THEN | ||
| do i = 1,InputFileData%NBody | ||
| IF ( InputFileData%FKMod(i) /= FKMod_none .and. InputFileData%FKMod(i) /= FKMod_full )THEN | ||
| CALL SetErrStat( ErrID_Fatal,'FKMod must be '//trim(num2lstr(FKMod_none))//' or '//trim(num2lstr(FKMod_full))//' for all WAMIT bodies.',ErrStat,ErrMsg,RoutineName) | ||
| RETURN | ||
| END IF | ||
| IF ( InputFileData%FKMod(i) == FKMod_full .and. InputFileData%Wamit%ExctnMod == 2 ) THEN | ||
| CALL SetErrStat( ErrID_Fatal,'FKMod = '//trim(num2lstr(FKMod_full))//' is incompatible with state-space wave excitation model (ExctnMod=2). Need ExctnMod = 0 or 1.',ErrStat,ErrMsg,RoutineName) | ||
| RETURN |
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To do before merge:
|
…=1 for consistency and backward compatibility (Copilot suggestion)
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Feature or improvement description
This PR adds mesh-based nonlinear Froude-Krylov and hydrostatic load calculation in HydroDyn for the potential-flow bodies. This is still a work in progress with only basic functionality implemented. More information to come.
Initially, the implementation will only support ASCII STL files. The algorithm only supports triangular patches. Clipping of the triangular patches at the instantaneous waterline is included for fast convergence on coarse mesh.
For potential-flow bodies with nonlinear FK and hydrostatics enabled. HydroDyn requires the *.3sc file from WAMIT, which only contains the linear scattering loads to avoid double-counting the Froude-Krylov part. It also automatically zeros out the hydrostatic loads from
PtfmVol0and the hydrostatic stiffness matrix. Any second-order potential-flow loads are also zeroed out. Note that forNBodyMod=1(coupled potential-flow bodies), nonlinear Froude-Krylov and hydrostatics must be enabled or disabled for all bodies together. For decoupled bodies (NBodyMod=2orNBodyMod=3), nonlinear FK and hydrostatics can be selectively enabled for some bodies. The new features are currently incompatible with generalized degrees of freedom withNAddDOF>0.HydroDyn Inputs
This PR introduces two new input lines at the very end of the
FLOATING PLATFORMsection of the HydroDyn input file.Output Channels
Added new output channels
B1NFKFxi,B1NFKFyi,B1NFKFzi,B1NFKMxi,B1NFKMyi,B1NFKMzi, ...,B9NFKMzi. These outputs provide the combined nonlinear Froude-Krylov and hydrostatic forces and moments on the first 9 potential-flow bodies. The forces and moments are in the earth-fixedxi,yi, andzidirections and the moments are about the instantaneous body reference point, same as other similar output channels. For performance reasons, HydroDyn does not compute separate nonlinear Froude-Krylov excitation and hydrostatic forces and moments; only the combined loading is available.Note that if nonlinear Froude-Krylov and hydrostatic calculation is enabled (
FKMod=1), the regular wave excitation output channels, e.g.,B1WvsFxiandB1WvsF1xi, will only give the linear scattering part of the wave excitation computed from the.3scfile. The linearized hydrostatic loads, e.g.,B1HdsFzi, will also be zeroed. The sum ofB1WvsFxiandB1NFKFxi, for example, gives the total (Froude-Krylov and scattering) wave excitation and hydrostatic loads onB1.Example results
The total hydrodynamic and hydrostatic loads on a shallow-draft (5 m) body with a small freeboard (2.5 m) are computed using the new mesh-based nonlinear Froude-Krylov and hydrostatic load implementation. The side wall of the body is also heavily tapered with a corner at the still water level.
The loads reported include the mesh-based Froude-Krylov and hydrostatic loads and the scattering part of the linear wave excitation from frequency-to-time-domain transformation. The body is fixed. The irregular incident waves have a significant wave height of 5 m and a peak period of 12 s, leading to strongly nonlinear loading.
To check convergence, three different meshes are used, ranging from 92 triangular faces to 2,010 faces.
Coarse mesh (92 faces)
Medium mesh (506 faces)
Fine mesh (2,010 faces)
Good convergence is observed across the different mesh resolutions, with only occasional small differences between the coarsest mesh with only 92 faces and the medium mesh with 506 faces. Furthermore, the loads from both the medium and the fine mesh are smooth, indicating the waterline face clipping is functioning correctly.
Surge force
Heave force
Pitch moment
Pitch moment (zoomed in)
Still requires
Impacted areas of the software
HydroDyn, openfast_io, docs, r-test
Generative AI usage
Co-authored-by: Google Gemini gemini@google.com
Test results, if applicable
Requires input file changes, but should not affect existing r-test results if the new features are not used. All existing r-test passed. Also added a new HydroDyn module r-test for the mesh-based load calculation.