Merge pull request #2017 from abhineet-gupta/YawFrictionImplementation

Yaw friction implementation

Author: andrew-platt

docs/OtherSupporting/OutListParameters.xlsx

@@ -72,6 +72,7 @@ def runDoxygen(sourcfile, doxyfileIn, doxyfileOut):
     'source/user/aerodyn-aeroacoustics/references.bib',
     'source/user/aerodyn-olaf/bibliography.bib',
     'source/user/aerodyn/bibliography.bib',
+    'source/user/elastodyn/bibliography.bib',
     'source/user/beamdyn/references.bib',
     'source/user/extptfm/bibliography.bib',
     'source/user/fast.farm/bibliography.bib',

docs/conf.py

@@ -0,0 +1,6 @@
+@techreport{ed-hammam2023,
+  title={Modeling the Yaw Behavior of Tail Fins for Small Wind Turbines: November 22, 2021-May 21, 2024},
+  author={Hammam, Mohamed M and Wood, David and Summerville, Brent},
+  year={2023},
+  institution={National Renewable Energy Laboratory (NREL), Golden, CO (United States)}
+}

docs/source/user/elastodyn/bibliography.bib

@@ -58,3 +58,4 @@ equations of FAST v7 and the ElastoDyn module of FAST v8 and OpenFAST.
    coordsys.rst
    input.rst
    theory.rst
+   zrefs.rst

docs/source/user/elastodyn/figs/YawFrictionModel.jpg

@@ -231,6 +231,17 @@ Rotor-Teeter
 **TeetHSSp**    - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
 
 
+Yaw-Friction
+~~~~~~~~~~~~
+
+**YawFrctMod**  - Yaw-friction model {0: none, 1: friction without Fz term at the yaw bearing, 2: friction includes Fz term at yaw bearing, 3: user defined model} 
+
+**M_CSmax**     - Maximum Coulomb friction torque (N-m)[mu_s*D_eff when YawFrctMod=1 and Fz*mu_s*D_eff when YawFrctMod=2]
+
+**M_CD**        - Dynamic friction moment at null yaw rate (N-m) [mu_d*D_eff when YawFrctMod=1 and Fz*mu_d*D_eff when YawFrctMod=2]
+
+**sig_v**       - Viscous friction coefficient (N-m/(rad/s))
+
 
 Drivetrain
 ~~~~~~~~~~

docs/source/user/elastodyn/index.rst

@@ -159,7 +159,41 @@ The total moment on the given degree of freedom is:
 
 
 
+.. _ed_yawfriction_theory:
 
+Yaw-friction
+------------
+A yaw-friction model is implemented in ElastoDyn based on a Coulomb-viscous approach.
+The yaw-friction moment as a function of yaw rate (:math:`\omega`) is shown below in :numref:`figYawFriction`
+
+.. _figYawFriction:
+.. figure:: figs/YawFrictionModel.jpg
+   :width: 60%
+           
+   Yaw-friction model
+
+The yaw-friction torque :math:`M_f` can be calcualated as follows.
+
+if :math:`\omega\neq0`:
+
+.. math::
+   M_f = \mu_d\bar{D}\times\text{min}(0,F_z)\times\text{sign}(\omega) - \sigma_v\times\omega  
+ 
+if :math:`\omega=0` and :math:`\dot{\omega}\neq 0`:
+
+.. math::
+   M_f = \mu_d\bar{D}\times\text{min}(0,F_z)\times\text{sign}(\dot{\omega})
+
+if :math:`\omega=0` and :math:`\dot{\omega}=0`:
+
+.. math::
+   M_f = -\text{min}(\mu_s\bar{D}\times|\text{min}(0,F_z)|,|M_z|)\times\text{sign}(M_z)
+
+
+where :math:`\bar{D}` is the effective yaw-bearing race diameter, :math:`\mu_d` is the dynamic friction coefficient, :math:`\mu_s` is the static friction coefficient, :math:`F_z` is effective axial load on yaw-bearing, :math:`M-z` is the external torque on yaw-bearing.
+The static 'stiction' (where the static contribution exceeds the dynamic Coulomb friction) is only applied if both the yaw rotational velocity and acceleration at the current time-step are zero.
+The static portion of the friction is omitted if the rotational acceleration is not null, (sign(0) is taken as 1).
+This is to account for the fact that a 'warm' joint may not feel stiction when crossing through zero velocity in a dynamic sense :cite:`ed-hammam2023`
 
 
 .. _ed_dev_notes:

docs/source/user/elastodyn/input.rst

@@ -0,0 +1,9 @@
+.. only:: html
+   
+   References
+   ----------
+
+.. bibliography:: bibliography.bib
+   :labelprefix: ed-
+
+

docs/source/user/elastodyn/theory.rst

@@ -101,6 +101,35 @@ SUBROUTINE UserTeet ( TeetDef, TeetRate, ZTime, DirRoot, TeetMom )
 RETURN
 END SUBROUTINE UserTeet
 !=======================================================================
+SUBROUTINE UserYawFrict ( ZTime, Fz, Mzz, Omg, OmgDot, DirRoot, YawFriMf )
+
+   ! This is a dummy routine for holding the place of a user-specified
+   ! Yaw Friction.  Modify this code to create your own device.
+
+
+USE                             Precision
+
+
+IMPLICIT                        NONE
+
+
+   ! Passed Variables:
+REAL(DbKi), INTENT(IN )      :: ZTime     ! Current simulation time, sec.
+REAL(R8Ki), INTENT(IN )      :: Fz, Mzz   ! Yaw Bering normal force (positive if upward) and torque, N and N*m
+REAL(R8Ki), INTENT(IN )      :: Omg       ! Yaw rotational speed, rad/s.
+REAL(R8Ki), INTENT(IN )      :: OmgDot    ! Yaw rotational acceleration, rad/s^2.
+
+CHARACTER(1024), INTENT(IN ) :: DirRoot             ! The name of the root file including the full path to the current working directory.  This may be useful if you want this routine to write a permanent record of what it does to be stored with the simulation results: the results should be stored in a file whose name (including path) is generated by appending any suitable extension to DirRoot.
+
+REAL(ReKi), INTENT(OUT)      :: YawFriMf        ! Yaw friction moment, N*m.
+
+
+
+YawFriMf = 0.0
+
+RETURN
+END SUBROUTINE UserYawFrict
+!=======================================================================
 SUBROUTINE UserTFrl ( TFrlDef, TFrlRate, ZTime, DirRoot, TFrlMom )