Modification of the WP-Baseline WEC

Dear Dr. Jonkman,
currently i’m trying to modify the WP_Baseline WEC to a real life WEC i have some basic information about. The WEC has a hub height of 65.0 meters and a rotor diameter of 43.7 m.

Testing is done with a steady wind (WindType1)

Fast is aborting with this failure message:

FAST (v8.16.00a-bjj, 27-Jul-2016)

Copyright (C) 2016 National Renewable Energy Laboratory

This program comes with ABSOLUTELY NO WARRANTY. See the “license.txt” file distributed with this
software for details.

Running FAST (v8.16.00a-bjj, 27-Jul-2016), compiled as a 64-bit application using single
linked with NWTC Subroutine Library (v2.09.00, 23-Jul-2016)

Heading of the FAST input file:
FAST Certification Test #11: WindPACT 1.5 MW Baseline with many DOFs undergoing a pitch

Running ElastoDyn (v1.04.00a-bjj, 26-Jul-2016).

Running AeroDyn14 (v14.05.01a-bjj, 25-Jul-2016).

Running InflowWind (v3.03.00, 26-Jul-2016).
Opening InflowWind input file:
Timestep: 0 of 20 seconds.

FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 0.195 s

formWind_CalcOutput:GetWindSpeed:Height must not be negative.
IfW_UniformWind_CalcOutput: Error calculating the wind speed at position (-8.8972, -192.85,
-23.123) in the wind-file coordinates
SolveOption2:AD14_CalcOutput:ELEMFRC:vindinf:Value of Rzero = 1.8992 must be smaller than 1 in

FAST encountered an error at simulation time 0.215 of 20 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.[/i]

the error occured after i scaled the blades in the xxx_Aerodyn_Dynin.dat file to the desired rotor diameter.

[i] 9 BldNodes - Number of blade nodes used for analysis (-)
RNodes AeroTwst DRNodes Chord NFoil PrnElm
2.8666700E+00 1.1100000E+01 2.233340E+00 1.1920000E+00 1 NOPRINT
5.1000100E+00 1.1100000E+01 2.233340E+00 1.3880000E+00 2 NOPRINT
7.3333500E+00 1.1100000E+01 2.233340E+00 1.5840000E+00 2 NOPRINT
9.5666900E+00 1.0410000E+01 2.233340E+00 1.6780000E+00 2 NOPRINT
1.1800030E+01 8.3800000E+00 2.233340E+00 1.3750000E+00 3 NOPRINT
1.4033370E+01 6.3500000E+00 2.233340E+00 1.0710000E+00 3 NOPRINT
1.6266710E+01 4.3300000E+00 2.233340E+00 9.7000000E-01 3 NOPRINT
1.8500050E+01 2.8500000E+00 2.233340E+00 7.8200000E-01 4 NOPRINT
2.0733390E+01 8.0000000E-02 2.233340E+00 6.0000000E-01 4 NOPRINT


Do you have any suggestions where to search the error?

Best regards
Florian Speicher

Dear Dr. Jonkman,

I found some kind of inconsistency. The actual hub heigth is 65.0 meters.
In the Elastodyn. sum file there is a calculated hub height of 64.398 meters.

Hub-Height (m) 64.398

How is this parameter calculated?

Dear Florian,

The hub-height (HubHt) written to the ElastoDyn summary file is calculated as:

HubHt = TowerHt + Twr2Shft + OverHang*SIN(ShftTilt)

My guess is your model is going numerically unstable because you’ve shortened the blades (effectively making them stiffer) without reducing the time step. Warnings regarding a “small angle approximation violation,” warnings regarding “supersonic blades,” a simulation crash, or very large deflections that occur in the time series are good signs of a numerical instability. Or use “Search…” in the upper right of the forum to search for “small angle assumption” to see how we’ve solved similar problems in the past.

Best regards,