Add User-defined wind documentation for InflowWind

docs/source/user/inflowwind/index.rst

@@ -19,4 +19,5 @@ InflowWind Users Guide and Theory Manual
 
    driver.rst
    input.rst
+   user_defined.rst
    appendix.rst

docs/source/user/inflowwind/user_defined.rst

@@ -0,0 +1,303 @@
+.. _ifw_user_defined:
+
+User-Defined Wind Fields
+=========================
+
+This section explains how to implement custom wind fields in InflowWind using ``WindType = 6``.
+
+Overview
+--------
+
+The user-defined wind field feature allows developers to implement custom wind models by:
+
+1. Defining a data structure to hold wind field parameters
+2. Initializing that data structure from input files or parameters  
+3. Implementing a function to return wind velocities at any position and time
+
+This is useful for:
+
+- Analytical wind models (e.g., vortex, wake models)
+- Custom wind profiles not available in standard formats
+- Coupling to external wind solvers
+- Real-time wind measurements from sensors
+- Research and development of new wind field representations
+
+.. important::
+   After modifying the registry files (``.txt`` files), you must rebuild the project 
+   to regenerate the type definition files (``*_Types.f90``). The modifications to the 
+   ``.txt`` files define the extended data structures, but they won't be available 
+   until after regeneration.
+
+Implementation Steps
+--------------------
+
+Step 1: Define Data Structure
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Edit ``modules/inflowwind/src/IfW_FlowField.txt`` and add fields to ``UserFieldType``:
+
+.. code-block:: text
+
+   typedef  ^              UserFieldType          ReKi                RefHeight           -     -         -     "reference height; used to center the wind"                   meters
+   typedef  ^              ^                      IntKi               NumDataLines        -     0         -     "number of data lines (for time-varying user wind)"          -
+   typedef  ^              ^                      DbKi                DTime               :     -         -     "time array for user-defined wind"                           seconds
+   typedef  ^              ^                      ReKi                Data                ::    -         -     "user-defined wind data array [NumDataLines, NumDataColumns]" -
+   typedef  ^              ^                      CHARACTER(1024)     FileName            -     -         -     "name of user wind file (if applicable)"                     -
+
+Add any custom fields needed for your wind model implementation.
+
+Step 2: Define Initialization Inputs  
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Edit ``modules/inflowwind/src/InflowWind_IO.txt`` and add fields to ``User_InitInputType``:
+
+.. code-block:: text
+
+   typedef  ^              User_InitInputType    CHARACTER(1024)         WindFileName            -     -     -     "name of file containing user-defined wind data (if applicable)" -
+   typedef  ^              ^                     ReKi                    RefHt                   -     -     -     "reference height for user wind field"                        meters
+   typedef  ^              ^                     IntKi                   NumDataColumns          -     0     -     "number of data columns in user wind file (if applicable)"    -
+
+Add any parameters needed to initialize your wind model.
+
+Step 3: Regenerate Type Files
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+After modifying the registry files, rebuild the project to regenerate type definitions. When using Visual Studio
+to build OpenFAST on Windows, the types files are automatically regenerated. When using CMake,
+run the following commands to enable generation of the types files.
+
+.. code-block:: bash
+
+   cd build
+   cmake .. -DGENERATE_TYPES=ON
+   make
+
+The build process automatically regenerates the ``*_Types.f90`` files from the ``.txt`` registry files.
+
+Step 4: Implement Initialization
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Edit ``modules/inflowwind/src/InflowWind_IO.f90`` and implement ``IfW_User_Init()``:
+
+.. code-block:: fortran
+
+   subroutine IfW_User_Init(InitInp, SumFileUnit, UF, FileDat, ErrStat, ErrMsg)
+      ! Initialize UF%RefHeight, read data files, allocate arrays
+      ! Set FileDat metadata (wind type, time range, spatial extent, etc.)
+      ! Write summary information to SumFileUnit if > 0
+   end subroutine
+
+This routine:
+
+- Reads any necessary input files specified in ``InitInp``
+- Allocates and populates the ``UserFieldType`` (``UF``) data structure
+- Sets appropriate metadata in the ``WindFileDat`` structure
+- Writes initialization information to the summary file
+
+Step 5: Implement Velocity Function
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Edit ``modules/inflowwind/src/IfW_FlowField.f90`` and implement ``UserField_GetVel()``:
+
+.. code-block:: fortran
+
+   subroutine UserField_GetVel(UF, Time, Position, Velocity, ErrStat, ErrMsg)
+      ! Use UF data to compute velocity at Position and Time
+      ! Position(1) = X, Position(2) = Y, Position(3) = Z (meters)
+      ! Return Velocity(1) = U, Velocity(2) = V, Velocity(3) = W (m/s)
+   end subroutine
+
+This function is called for each position where wind velocities are needed during simulation.
+
+Coordinate Systems
+------------------
+
+Input Coordinates (Position)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- **X**: Downstream direction (after rotation applied by InflowWind)
+- **Y**: Lateral/crosswind direction  
+- **Z**: Vertical direction (measured from ground, Z=0 is ground level)
+- **Units**: meters
+
+Output Velocities (Velocity)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- **U**: Velocity component along X (positive = downwind)
+- **V**: Velocity component along Y (positive = to the left when looking downwind)
+- **W**: Velocity component along Z (positive = upward)
+- **Units**: m/s
+
+.. note::
+   InflowWind handles the rotation between global coordinates and wind coordinates. 
+   Your implementation should work in the wind coordinate system where X is aligned 
+   with the mean wind direction.
+
+Example Implementation
+----------------------
+
+Power-Law Wind Profile
+~~~~~~~~~~~~~~~~~~~~~~
+
+This example implements a simple power-law wind profile.
+
+**Velocity Function** (in ``IfW_FlowField.f90``):
+
+.. code-block:: fortran
+
+   subroutine UserField_GetVel(UF, Time, Position, Velocity, ErrStat, ErrMsg)
+      type(UserFieldType), intent(in)     :: UF
+      real(DbKi), intent(in)              :: Time
+      real(ReKi), intent(in)              :: Position(3)
+      real(ReKi), intent(out)             :: Velocity(3)
+      integer(IntKi), intent(out)         :: ErrStat
+      character(*), intent(out)           :: ErrMsg
+
+      real(ReKi)                          :: RefSpeed, Exponent, Height
+
+      ErrStat = ErrID_None
+      ErrMsg = ""
+
+      ! Get reference speed and exponent from UF%Data
+      RefSpeed = UF%Data(1, 1)  ! Reference wind speed (m/s)
+      Exponent = UF%Data(1, 2)  ! Power law exponent
+      Height = Position(3)       ! Height above ground
+
+      ! Apply power law: U(z) = Uref * (z/zref)^alpha
+      if (Height > 0.0_ReKi) then
+         Velocity(1) = RefSpeed * (Height / UF%RefHeight)**Exponent
+         Velocity(2) = 0.0_ReKi  ! No lateral wind
+         Velocity(3) = 0.0_ReKi  ! No vertical wind
+      else
+         Velocity = 0.0_ReKi  ! Below ground
+      end if
+
+   end subroutine
+
+**Initialization** (in ``InflowWind_IO.f90``):
+
+.. code-block:: fortran
+
+   subroutine IfW_User_Init(InitInp, SumFileUnit, UF, FileDat, ErrStat, ErrMsg)
+      ! ... (declarations)
+
+      ErrStat = ErrID_None
+      ErrMsg = ""
+
+      ! Set reference height
+      UF%RefHeight = InitInp%RefHt
+
+      ! Allocate data array for [RefSpeed, Exponent]
+      UF%NumDataLines = 1
+      call AllocAry(UF%Data, 1, 2, 'User wind data', TmpErrStat, TmpErrMsg)
+      call SetErrStat(TmpErrStat, TmpErrMsg, ErrStat, ErrMsg, RoutineName)
+      if (ErrStat >= AbortErrLev) return
+
+      ! Set values (could read from file instead)
+      UF%Data(1, 1) = 10.0_ReKi  ! 10 m/s reference speed
+      UF%Data(1, 2) = 0.2_ReKi   ! Power law exponent
+
+      ! Set metadata
+      FileDat%WindType = 6
+      FileDat%RefHt = UF%RefHeight
+      FileDat%MWS = UF%Data(1, 1)
+      FileDat%RefHt_Set = .true.
+      ! ... (set other FileDat fields as needed)
+
+   end subroutine
+
+Common Use Cases
+----------------
+
+Steady Analytical Wind Field
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Define wind as a function of position only (ignore ``Time`` parameter).
+
+**Example**: Logarithmic wind profile, vortex wind field, uniform flow with shear.
+
+Time-Varying Wind Field  
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Store wind data in time series arrays and interpolate based on ``Time`` parameter.
+
+**Example**: Measured wind data, prescribed wind transients, wake models.
+
+Wind from External Solver
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Call external functions to get instantaneous wind fields.
+
+**Example**: CFD coupling, external wake models, prescribed turbulence.
+
+Real-Time Sensor Data
+~~~~~~~~~~~~~~~~~~~~~
+
+Load measured wind data from sensors and interpolate spatially/temporally.
+
+**Example**: LIDAR measurements, met mast data, field measurements.
+
+Limitations and Considerations
+-------------------------------
+
+Current Limitations
+~~~~~~~~~~~~~~~~~~~
+
+1. **No Acceleration Support**: User-defined wind fields do not currently support 
+   acceleration calculations needed by some modules (e.g., MHK turbines).
+
+Performance Considerations
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- ``UserField_GetVel()`` is called for every point at every time step
+- Implement efficiently; pre-compute values in ``IfW_User_Init()`` when possible
+- Consider caching or interpolation strategies for complex calculations
+
+Error Handling
+~~~~~~~~~~~~~~
+
+- Always validate input parameters in ``IfW_User_Init()``
+- Check array bounds in ``UserField_GetVel()``
+- Verify Position and Time values are within valid ranges
+- Use ``SetErrStat()`` to report errors appropriately
+
+Best Practices
+--------------
+
+1. **Start Simple**: Begin with analytical models before implementing complex wind fields
+
+2. **Document Thoroughly**: Add detailed comments explaining your implementation and any file formats
+
+3. **Use SI Units**: Always use meters, seconds, and m/s
+
+4. **Pre-compute**: Calculate as much as possible during initialization rather than runtime
+
+5. **Validate**: Test with known analytical solutions before using in production
+
+6. **Handle Boundaries**: Implement appropriate behavior for points outside valid domain
+
+7. **Report Metadata**: Properly populate ``WindFileDat`` with time range, spatial extent, etc.
+
+File Locations
+--------------
+
+==========================================  ==========================================================
+File                                        Purpose
+==========================================  ==========================================================
+``modules/inflowwind/src/``                 Source code directory
+``IfW_FlowField.txt``                       Type definitions for flow field data structures
+``InflowWind_IO.txt``                       Type definitions for initialization inputs
+``IfW_FlowField.f90``                       Flow field implementation (``UserField_GetVel()``)
+``InflowWind_IO.f90``                       Initialization implementation (``IfW_User_Init()``)
+``IfW_FlowField_Types.f90``                 Auto-generated type definitions (regenerated from .txt)
+``InflowWind_IO_Types.f90``                 Auto-generated type definitions (regenerated from .txt)
+==========================================  ==========================================================
+
+Additional Resources
+--------------------
+
+- See the original :download:`InflowWind Manual <InflowWind_Manual.pdf>` for general InflowWind information
+- Review existing wind field implementations (Uniform, Grid3D) in the source code for reference
+- Check :ref:`ifw_appendix` for example input files
+- Refer to NWTC Library documentation for array allocation and error handling utilities
+- See :ref:`ifw_angles` for information about wind coordinate systems and rotations