SoilDyn/SubDyn: reaction loads when REDWIN is used

[RBergua]

This PR is ready to be merged.

Feature or improvement description
The proposed code introduces a new flag (SlDNonLinear) to pass from SoilDyn to SubDyn in order to correctly identify when SoilDyn is computing nonlinear soil reaction forces (REDWIN DLL, CalcOption=3).

The new flag SlDNonLinear is set internally in SoilDyn based on CalcOption, ensuring it is only TRUE when the REDWIN DLL is active. When nonlinear forces are active, SubDyn reaction outputs (ReactSS) are set to NaN to prevent the user from using reaction loads that only have the linear part. Users should instead use the SoilDyn output sensors (e.g., Sld1Fxg, Sld1Fyg) which correctly account for the total soil reaction at each node.

Additionally, the linear soil stiffness transfer from SoilDyn to SubDyn is now better documented in the console (SoilDyn: linear stiffness passed directly to SubDyn as a stiffness matrix).

For reference, in the current code before these changes, SlDNonLinearForcePortionOnly seems to be defined as TRUE whenever SoilDyn is called, regardless of whether nonlinear forces are actually being computed. This seems a bit confusing. See at the bottom the "Future improvements?" part.

Related issue, if one exists
This PR addresses issues #3317 and #3318

Impacted areas of the software
SubDyn reaction load sensor when REDWIN (CalcOption = 3 in SoilDyn) is used.
SoilDyn messages in the console at run time.

Test results, if applicable
This PR impacts the SubDyn outputs ReactFXss, ReactFYss, ReactFZss, ReactMXss, ReactMYss, ReactMZss. However, there are no r-test cases with REDWIN. So, no differences are expected.

For verification purposes, you can find examples of the new messages and results below:
CalcOption = 1 uses a linear stiffness matrix.

In this case all sensors (SubDyn and SoilDyn) are available:

CalcOption: 3 uses a linear stiffness matrix AND non-linear forces computed by REDWIN.

In this case, the reaction loads from SubDyn return NaN. The proper results (including the linear and nonlinear part) are available in SoilDyn.

Additional information: some drama compiling OpenFAST...
I tried to compile OpenFAST in Visual Studio Code by means of GCC. Although I could compile without issues, when I executed the code I ended up with the issues reported here: #3301

Then I decided to move to GitHub Actions and compile with Intel Fortran Compiler. @andrew-platt Somehow, when running the deploy.yml, GitHub was not generating from scratch the SubDyn_Types.f90 file based on my updated SubDyn_Registry.txt. I'm not sure if this is a limitation of the deploy.yml approach. To overcome this, I took the updated SubDyn_Types.f90 from my local run in Visual Studio Code and added it to my branch: 67db890.

Future improvements?
When looking at the Calc_StiffDamp and Calc_REDWIN in the SoilDyn.f90 file, the linear and nonlinear loads are computed as expected. However, we can find the condition: if (p%SlDNonLinearForcePortionOnly) then in several places. I do believe this is indeed always TRUE and could be removed. But I'm not sure if there was a reason for it during the development.

[Copilot]

Pull request overview

This PR fixes misleading SubDyn reaction load outputs when SoilDyn is using REDWIN (nonlinear soil reactions) by propagating a nonlinear-SSI flag from SoilDyn to SubDyn and invalidating SubDyn’s ReactSS outputs in that mode.

Changes:

• Add a new SlDNonLinear flag to SubDyn init/parameter types (registry + generated types) to indicate nonlinear SoilDyn reactions are active.
• Pass SlDNonLinear from SoilDyn (via glue code) to SubDyn and set ReactSS outputs to NaN when nonlinear SoilDyn loads are enabled.
• Update SoilDyn console messaging to clarify stiffness transfer and REDWIN nonlinear load usage.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
modules/subdyn/src/SubDyn_Types.f90	Adds SlDNonLinear to SubDyn init/param types and updates copy/pack/unpack.
modules/subdyn/src/SubDyn_Registry.txt	Registers SlDNonLinear in InitInput and Parameter types for code generation/serialization.
modules/subdyn/src/SubDyn_Output.f90	Sets ReactSS outputs to NaN when SlDNonLinear is true.
modules/subdyn/src/SubDyn.f90	Copies SlDNonLinear from init input into p for runtime access.
modules/soildyn/src/SoilDyn.f90	Updates console output to better explain linear stiffness transfer and REDWIN nonlinear loads.
modules/openfast-library/src/FAST_Subs.f90	Sets Init%InData_SD%SlDNonLinear based on SoilDyn’s REDWIN interface usage.

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[andrew-platt]

Oops. I meant to put this on rc-5.0.1. Will open a PR to backport it.