OpenFAST v5.0.0 Simulink Windows binaries: DLL name mismatch breaks FAST_SFunc.mexw64

[Mohammad-Salik]

Bug description

Simulink MEX S-function FAST_SFunc.mexw64 fails to load on Windows due to a DLL dependency name mismatch in the OpenFAST v5.0.0 precompiled Windows binaries release assets. The MEX expects OpenFAST-Simulink_Matlab_Release.dll, but the asset provides OpenFAST-Simulink.dll. Renaming the DLL to the expected name makes the simulation work.

To Reproduce

Steps to reproduce the behavior:

1. Download OpenFAST v5.0.0 from GitHub Releases → Assets → Precompiled Windows Binaries.
2. Use the provided Simulink interface files from that package (FAST_SFunc.mexw64 and the Simulink DLL).
3. In MATLAB/Simulink, open a model that uses the S-Function block FAST_SFunc (e.g., .../FAST Nonlinear Wind Turbine/S-Function) and start simulation.
4. Observe error:

Invalid MEX-file 'E:\HL_Simulations\FAST_SFunc.mexw64': The specified module could not be found.

5. Using the “Dependencies” tool on FAST_SFunc.mexw64 shows it requires OpenFAST-Simulink_Matlab_Release.dll, but the release asset provides OpenFAST-Simulink.dll.

Expected behavior

The precompiled Windows binaries should contain a Simulink DLL whose filename matches what FAST_SFunc.mexw64 is linked against, so the MEX loads without manual renaming.

OpenFAST Version

**************************************************************************************************
 OpenFAST
 Copyright (C) 2026 National Renewable Energy Laboratory
 Copyright (C) 2026 Envision Energy USA LTD
 This program is licensed under Apache License Version 2.0 and comes with ABSOLUTELY NO WARRANTY.
 See the "LICENSE" file distributed with this software for details.
 **************************************************************************************************
 OpenFAST-unversioned
 Compile Info:
  - Compiler: Intel(R) Fortran Compiler 20250302
  - Architecture: 64 bit
  - Precision: single
  - OpenMP: No
  - Date: Mar 13 2026
  - Time: 19:07:51
 Execution Info:
  - Date: 03/19/2026
  - Time: 13:49:12+0100

System Information

• OS: Windows 11 Pro (Build 26200)
• MATLAB/Simulink: R2025b Update 4

Additional context

• In OpenFAST v4.2.0 the dependency was OpenFAST-Simulink_x64.dll and the provided file naming matched, so the MEX loaded without issues.
• Workaround: rename OpenFAST-Simulink.dll to OpenFAST-Simulink_Matlab_Release.dll. After renaming, the Simulink simulation runs correctly.

---

[andrew-platt]

Thanks for bringing this to our attention. We will revise the mex function to use the OpenFAST-Simulink.dll name in the next release.

[LeeGoShawn]

thx, this helps me a lot. I am using the current version 5.0.0, but all the tutorials I found online are for older versions. even though I followed the steps strictly for debugging, Matlab still kept reporting errors. only then did I come across your discovery of the bug and realized it was a naming issue. I might have spent a lot more time debugging without your mention, LOL.