Wave inputs required for onshore DLC 1.2

[Rian-Bitencourt]

While using WEIS for onshore OpenFAST simulations, I noticed that the DLC generation workflow still required several wave/metocean inputs, even when hydrodynamics were disabled. In particular, DLC 1.2 required fatigue-related wave fields such as wave_height_fatigue, wave_period_fatigue, and wave_direction_fatigue. This seemed weird for onshore cases, where no wave loading should be involved.

From what I understood, gc_LoadInputs.py passed metocean_conditions directly to DLCGenerator, without checking whether the case was onshore or whether HydroDyn/SeaState was active. Then, inside dlc_generator.py, DLC 1.2 explicitly checked for wave-related fatigue entries and raised an exception if they were missing. As a result, to run onshore DLC 1.2 cases, I was forced to use artificial wave inputs, even though these inputs were not physically relevant.

In the dlc_generator.py, DLC 1.2 required the following metocean fields:

 def generate_1p2(self, dlc_options):
    # Power production normal turbulence model - fatigue loads
    
    # Get default options
    dlc_options.update(self.default_options)   

    # Error catching
    entries = [
        'wave_height_fatigue',
        'wave_period_fatigue',
        'wind_direction_fatigue',
        'wave_direction_fatigue',
        'probability',
    ]

    # Check for required inputs
    for input in entries + ['wind_speed_fatigue']:
        if len(self.metocean[input]) == 0:
            raise Exception(f'DLC 1.2 is selected, but the input {input} is required and missing from modeling.DLC_Driver.metocean')

This means that wave-related fatigue data were mandatory for DLC 1.2, regardless of whether the model was offshore or onshore. Since I am currently working on a specific onshore turbine with DLC 1.2 case, and I am not fully sure what the ideal way to handle this situation in WEIS would be, I decided to implement a simple defensive workaround. The main goal was to avoid having to manually define meaningless wave inputs for onshore cases. To do that, I added a preprocessing step in gc_LoadInputs.py. The idea was to automatically populate dummy wave/metocean fields when HydroDyn is disabled.

if self.modeling_options["OpenFAST"]["hydro"].get("CompHydro", 1) == 0:
    n_ws = len(metocean["wind_speed"])

    metocean["wave_height_NSS"] = [0.0] * n_ws
    metocean["wave_period_NSS"] = [1.0] * n_ws
    metocean["wave_height_SSS"] = [0.0] * n_ws
    metocean["wave_period_SSS"] = [1.0] * n_ws

    metocean["wave_height_fatigue"] = [0.0] * n_ws
    metocean["wave_period_fatigue"] = [1.0] * n_ws
    metocean["wave_direction_fatigue"] = [0.0] * n_ws
    metocean["wind_direction_fatigue"] = [0.0] * n_ws

    metocean["wave_height50"] = 0.0
    metocean["wave_period50"] = 1.0
    metocean["wave_height1"] = 0.0
    metocean["wave_period1"] = 1.0

    metocean["probability"] = [1.0 / n_ws] * n_ws
    metocean["wind_speed_fatigue"] = list(metocean.get("wind_speed"))

Note: The dummy values were chosen to be neutral for onshore cases and the period was set to 1.0 instead of 0.0 to avoid possible zero-period numerical or validation issues.

I also added a second protection directly inside generate_1p2() to auto-fill missing fatigue fields before the original DLC 1.2 validation logic is reached:

  n_ws = len(self.metocean.get("wind_speed", []))
  
  self.metocean.setdefault(
      "wind_speed_fatigue",
      list(self.metocean.get("wind_speed", []))
  )
  
  self.metocean.setdefault("wave_height_fatigue", [0.0] * n_ws)
  self.metocean.setdefault("wave_period_fatigue", [1.0] * n_ws)
  self.metocean.setdefault("wind_direction_fatigue", [0.0] * n_ws)
  self.metocean.setdefault("wave_direction_fatigue", [0.0] * n_ws)
  self.metocean.setdefault("probability", [1.0 / n_ws] * n_ws)

This is mainly a local and defensive workaround, not necessarily what I would consider the ideal long-term solution. It is now working for my current onshore DLC 1.2 case, but I would appreciate any guidance on whether there is already an intended mechanism in WEIS to handle this situation more cleanly.

It is also possible that I misunderstood part of the DLC/metocean workflow. If this is indeed a relevant topic, I would be happy to share more details, including the input files and the specific code sections I modified.

Thank you in advance for any guidance on this. In any case, thanks for all the great work on WEIS, it is a very useful tool :)

[dzalkind]

Hi Rian,

Thanks for the heads up! I think you've found and encoded a decent workaround.

There's no harm in using dummy values if the SeaState module is not used. I'll use this as a starting point and include a fix in the next version.

Best, Dan