OpenFAST · rafmudaf · Aug 6, 2021 · Sep 29, 2019 · Sep 22, 2020 · Sep 28, 2020
diff --git a/docs/source/user/hydrodyn/appendix.rst b/docs/source/user/hydrodyn/appendix.rst
diff --git a/docs/source/user/hydrodyn/figs/current_sub_models.jpg b/docs/source/user/hydrodyn/figs/current_sub_models.jpg
diff --git a/docs/source/user/hydrodyn/future_work.rst b/docs/source/user/hydrodyn/future_work.rst
@@ -0,0 +1,59 @@
+Future Work
+===========
+
+This list contains features that could be implemented in future
+releases:
+
+*  Enable times-series input motions for Morison members in the
+   standalone HydroDyn (**MorisonInputsMod** = 2)
+
+*  Enable tight-coupling to FAST, including linearization.
+
+*  Enable wave stretching (**WaveStMod** > 0).
+
+*  Enable full support for floating platform force flags.
+
+*  Enable joint overlap calculations (**JointOvrlp** = 1).
+
+*  Enable auto-generation of all possible output channels (**OutAll** =
+   TRUE).
+
+*  Add outputs pertaining to the total hydrodynamic applied loads at
+   nodes along members and at joints.
+
+*  Ensure that the output channels are written in the order they are
+   entered.
+
+*  Allow for a WAMIT reference point location other than (0,0,0).
+
+*  Allow **RdtnDT** to be independent from the FAST simulation time
+   step.
+
+*  Add distributed axial viscous-drag loads on tapered members.
+
+*  Add rotational inertia terms for fluid-filled members and marine
+   growth.
+
+*  Calculate the effective 6x6 added-mass matrix from strip-theory
+   members and place in the HydroDyn summary file.
+
+*  Add graphics/animation capability to visualize the substructure
+   geometry and motion, wave elevation, and hydrodynamic loads.
+
+*  Add convective fluid acceleration terms.
+
+*  Allow for wave directional spreading to include energy spectra that
+   varies with direction (requires changing from the equal-energy
+   method).
+
+*  Add higher order regular wave kinematics models for fixed-bottom
+   substructures.
+
+*  Add breaking wave-impact loads for fixed-bottom substructures.
+
+*  Add floating platform hydro-elastics.
+
+*  Add pressure mapping for floating platforms.
+
+*  Added automated computation and use of hydrostatic restoring matrix
+   for strip-theory members.
diff --git a/docs/source/user/hydrodyn/getting_started.rst b/docs/source/user/hydrodyn/getting_started.rst
@@ -0,0 +1,45 @@
+.. _hd-getting-started:
+
+Installation and Getting Started
+================================
+HydroDyn is included in the OpenFAST software repository and consists
+of two major components:
+
+* `hydrodyn_driver` is the standalone HydroDyn executable
+* `hydrodynlib` is the OpenFAST module library; it is most commonly
+  used when driven through the HydroDyn driver or the OpenFAST glue code  
+
+For installation instructions, see :ref:`installation`. In sections where
+an installation target can be specific, use `hydrodyn_driver`.
+
+Running the HydroDyn Driver
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The HydroDyn Driver has a simple command line interface:
+
+.. code-block:: bash
+
+    hydrodyn_driver <input_file>
+
+where `input_file` is the file described in :ref:`hd-driver-input`.
+Additional input files are required, including the :ref:`hd-primary-input`.
+The time-series output as well as other output from HydroDyn are
+described in :ref:`hd-output`.
+
+Running HydroDyn coupled to OpenFAST
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To run an OpenFAST simulation with the HydroDyn module enabled, the
+`CompHydro` flag must be switched on and the :ref:`hd-primary-input`
+path supplied in the OpenFAST primary input file:
+
+.. code-block::
+
+    # In the "Feature switches" section
+    1               CompHydro   - Compute hydrodynamic loads (switch) {0=None; 1=HydroDyn}
+
+    # In the "Input files" section
+    "HydroDyn.dat"  HydroFile   - Name of file containing hydrodynamic input parameters (quoted string)
+
+The time-series output as well as other output from HydroDyn are
+described in :ref:`hd-output`.
diff --git a/docs/source/user/hydrodyn/index.rst b/docs/source/user/hydrodyn/index.rst
@@ -0,0 +1,120 @@
+HydroDyn User Guide and Theory Manual
+=====================================
+
+.. toctree::
+   :maxdepth: 1
+
+   getting_started.rst
+   input_files.rst
+   output_files.rst
+   modeling_considerations.rst
+   future_work.rst
+   zrefs.rst
+   appendix.rst
+
+HydroDyn is a time-domain hydrodynamics module that has been coupled
+into the OpenFAST wind turbine
+multi-physics engineering tool to enable aero-hydro-servo-elastic
+simulation of offshore wind turbines. HydroDyn is applicable to both
+fixed-bottom and floating offshore substructures. The current release of
+HydroDyn integrates with OpenFAST through the FAST modularization framework.
+HydroDyn can also be driven as a standalone code to compute hydrodynamic
+loading uncoupled from OpenFAST.
+
+HydroDyn allows for multiple approaches for calculating the hydrodynamic
+loads on a structure:
+
+* Potential-flow theory solution
+* Strip-theory solution
+* Hybrid combination of the tower
+
+Waves generated internally
+within HydroDyn can be regular (periodic) or irregular (stochastic) and
+long-crested (unidirectional) or short-crested (wave energy spread
+across a range of directions). Wave elevations or full wave kinematics
+can also be generated externally and used within HydroDyn. Internally,
+HydroDyn generates waves analytically for finite depth using first-order
+(linear Airy) or first plus second-order wave theory :cite:`SharmaDean:1981`
+with the option to include directional spreading, but wave
+kinematics are only computed in the domain between the flat seabed and
+still-water level (SWL) and no wave stretching or higher order wave
+theories are included. The second-order hydrodynamic implementations
+include time-domain calculations of difference- (mean- and slow-drift-)
+and sum-frequency terms. To minimize computational expense, Fast Fourier
+Transforms (FFTs) are applied in the summation of all wave frequency
+components.
+
+The potential-flow solution is applicable to substructures or members of
+substructures that are large relative to a typical wavelength. The
+potential-flow solution involves either frequency-to-time-domain
+transforms or fluid-impulse theory (FIT). In the former, potential-flow
+hydrodynamic loads include linear hydrostatic restoring, the added mass
+and damping contributions from linear wave radiation (including
+free-surface memory effects), and the incident-wave excitation from
+first- and second-order diffraction (Froude-Kriloff and scattering). The
+hydrodynamic coefficients (first and second order) required for the
+potential-flow solution are frequency dependent and must be supplied by
+a separate frequency-domain panel code (e.g., WAMIT) from a
+pre-computation step. The radiation memory effect can be calculated
+either through direct time-domain convolution or through a linear
+state-space approach, with a state-space model derived through the
+`SS_Fitting <https://www.nrel.gov/wind/nwtc/ss-fitting.html>`_
+preprocessor. The second-order terms can be derived from the full
+difference- and sum-frequency quadratic transfer functions (QTFs) or the
+difference-frequency terms can be estimated via Standing et al.’s :cite:`Standing:1987`
+extension to Newman’s approximation, based only on first-order
+coefficients. The use of FIT is not yet documented in this manual.
+
+The strip-theory solution may be preferable for substructures or members
+of substructures that are small in diameter relative to a typical
+wavelength. Strip-theory hydrodynamic loads can be applied across
+multiple interconnected members, each with possible incline and taper,
+and are derived directly from the undisturbed wave and current
+kinematics at the undisplaced position of the substructure. The
+strip-theory loads include the relative form of Morison’s equation for
+the distributed fluid-inertia, added-mass, and viscous-drag components.
+Additional distributed load components include axial loads from tapered
+members and static buoyancy loads. Hydrodynamic loads are also applied
+as lumped loads on member endpoints (called joints). It is also possible
+to include flooding or ballasting of members, and the effects of marine
+growth. The hydrodynamic coefficients required for this solution come
+through user-specified dynamic-pressure, added-mass, and viscous-drag
+coefficients.
+
+For some substructures and sea conditions, the hydrodynamic loads from a
+potential-flow theory should be augmented with the loads brought about
+by flow separation.  For this, the viscous-drag component of the
+strip-theory solution may be included with the potential-flow theory
+solution.  Another option available is to supply a global damping matrix
+(linear or quadratic) to the system to represent this effect.
+
+When HydroDyn is coupled to OpenFAST, HydroDyn receives the position,
+orientation, velocities, and accelerations of the (rigid or flexible)
+substructure at each coupling time step and then computes the
+hydrodynamic loads and returns them back to OpenFAST. At this time,
+OpenFAST’s ElastoDyn structural-dynamics module assumes for a floating platform
+that the substructure (floating platform) is a six degree-of-freedom
+(DOF) rigid body. For fixed-bottom offshore wind turbines, OpenFAST’s SubDyn
+module allows for structural flexibility of multi-member substructures
+and the coupling to HydroDyn includes hydro-elastic effects.
+
+The primary HydroDyn input file defines the substructure geometry,
+hydrodynamic coefficients, incident wave kinematics and current,
+potential-flow solution options, flooding/ballasting and marine growth,
+and auxiliary parameters. The geometry of strip-theory members is
+defined by joint coordinates of the undisplaced substructure in the
+global reference system, with the origin at the intersection of the
+undeflected tower centerline with mean sea level (MSL). A member
+connects two joints; multiple members can use a common joint. The
+hydrodynamic loads are computed at nodes, which are the resultant of
+member refinement into multiple (**MDivSize** input) elements (nodes are
+located at the ends of each element), and they are calculated by the
+module. Member properties include outer diameter, thickness, and
+dynamic-pressure, added-mass and viscous-drag coefficients. Member
+properties are specified at the joints; if properties change from one
+joint to the other, they will be linearly interpolated for the inner
+nodes.
+
+See :ref:`hd-getting-started` for details on how to download or
+compile the HydroDyn and OpenFAST software executables, as well as
+instructions for running HydroDyn standalone and coupled to OpenFAST.