Regarding BeamDyn Usage

Wind & Water Structural Analysis
1

Dear everyone,

I am currently using BeamDyn for simulating the behavior of a 5MW wind turbine blade and have encountered some unexpected results.

In my simulation, I applied a tip load of 100N while setting gravitational acceleration to zero and ensuring a damping-free condition. Under these conditions, I expected the blade tip deformation to exhibit smooth, regular oscillations around an equilibrium position, similar to the steady-state deformation results obtained with OpenFAST under uniform inflow conditions. However, the results from BeamDyn appear unusual and do not match this expected behavior.

I have attached the BeamDyn results and the case setup for your reference. Could you please help me understand why these discrepancies might be occurring? Any insights or suggestions would be greatly appreciated.

The following shows the deformation in the x-direction at the blade tip.​​

TipTDxr
TipTDxr1848×953 141 KB

Here is my case setup.

------- BEAMDYN V1.00.00 Driver INPUT FILE -------------------------------------
Dynamic analysis of rotating NREL 5MW blade under gravity force
---------------------- SIMULATION CONTROL --------------------------------------
0 t_initial - Starting time of simulation (s)
20.0 t_final - Ending time of simulation (s)
0.001 dt - Time increment size (s)
---------------------- GRAVITY PARAMETER --------------------------------------
0.0 Gx - Component of gravity vector along X direction (m/s^2)
0.0 Gy - Component of gravity vector along Y direction (m/s^2)
0.0 Gz - Component of gravity vector along Z direction (m/s^2)
---------------------- FRAME PARAMETER --------------------------------------
0.0 GlbPos(1) - Component of position vector of the reference blade frame along X direction (m)
0.0 GlbPos(2) - Component of position vector of the reference blade frame along Y direction (m)
1.0 GlbPos(3) - Component of position vector of the reference blade frame along Z direction (m)
—The following 3 by 3 matrix is the direction cosine matirx ,GlbDCM(3,3),
—relates global frame to reference blade frame
1.000E+00 0.000E+00 0.000E+00
0.000E+00 1.000E+00 0.000E+00
0.000E+00 0.000E+00 1.000E+00
---------------------- ROOT VELOCITY PARAMETER ----------------------------------
0.0 RootVel(4) - Component of angular velocity vector of the beam root about X axis (rad/s)
0.0 RootVel(5) - Component of angular velocity vector of the beam root about Y axis (rad/s)
0.0 RootVel(6) - Component of angular velocity vector of the beam root about Z axis (rad/s)
---------------------- APPLIED FORCE ----------------------------------
0.0 DistrLoad(1) - Component of distributed force vector along X direction (N/m)
0.0 DistrLoad(2) - Component of distributed force vector along Y direction (N/m)
0.0 DistrLoad(3) - Component of distributed force vector along Z direction (N/m)
0.0 DistrLoad(4) - Component of distributed moment vector along X direction (N-m/m)
0.0 DistrLoad(5) - Component of distributed moment vector along Y direction (N-m/m)
0.0 DistrLoad(6) - Component of distributed moment vector along Z direction (N-m/m)
100.0 TipLoad(1) - Component of concentrated force vector at blade tip along X direction (N)
0.0 TipLoad(2) - Component of concentrated force vector at blade tip along Y direction (N)
0.0 TipLoad(3) - Component of concentrated force vector at blade tip along Z direction (N)
0.0 TipLoad(4) - Component of concentrated moment vector at blade tip along X direction (N-m)
0.0 TipLoad(5) - Component of concentrated moment vector at blade tip along Y direction (N-m)
0.0 TipLoad(6) - Component of concentrated moment vector at blade tip along Z direction (N-m)
---------------------- PRIMARY INPUT FILE --------------------------------------
“Dynamic_BeamDyn_Input_5MW.inp” InputFile - Name of the primary input file

------- BEAMDYN V1.00.* INDIVIDUAL BLADE INPUT FILE --------------------------
NREL5MW Blade
---------------------- BLADE PARAMETERS --------------------------------------
49 station_total - Number of blade input stations (-)
0 damp_type - Damping type (switch): 0: no damping; 1: viscous damping
---------------------- DAMPING COEFFICIENT------------------------------------
mu1 mu2 mu3 mu4 mu5 mu6
(s) (s) (s) (s) (s) (s)
1.0e-3 1.0e-3 1.0e-3 1.0e-3 1.0e-3 1.0e-3

--------- BEAMDYN V1.01.* INPUT FILE -------------------------------------------
NREL 5MW blade primary input file
---------------------- SIMULATION CONTROL --------------------------------------
False Echo - Echo input data to “.ech” (flag)
2 analysis_type - 1: Static analysis; 2: Dynamic analysis (switch)
0.0 rhoinf - Numerical Damping Parameter for Generalized-alpha integrator
2 quadrature - 1: Gauss; 2: Trapezoidal (switch)
DEFAULT refine - Refinement factor for quadrature 2 (-). DEFAULT = 1
DEFAULT n_fact - Factorization frequency (-). DEFAULT = 5
DEFAULT DTBeam - Time step size (s).
DEFAULT NRMax - Max number of iterations in Newton-Ralphson algorithm (-). DEFAULT = 10
DEFAULT stop_tol - Tolerance for stopping criterion (-)

Thank you for your time and assistance.

Best regards,

2

Dear @Min.Li,

Your results are what I would expect. The tip load will not excite a single mode, but rather multiple modes, so, you’ll see multiple frequencies in the response. And without damping, the response of various modes will not damp out and a steady-state condition will not be reached.

Best regards,

3

Dear @Jason.Jonkman ,

Thank you very much for your previous response. I have fully understood the information you shared.

I would like to follow up with a question regarding OpenFAST when using BeamDyn for calculating blade tip deflection: is the observed steady oscillation in the deformation due to the use of only a single mode? If so, is there a setting or switch to control this, and can this be adjusted within the code?

Looking forward to your reply.

Best regards,

4

Dear @Min.Li,

I’m not sure what you mean by “observed steady oscillation”.

Regardless, BeamDyn does not make use of natural modes in its solve, but rather, BeamDyn’s degrees of freedom (DOFs) are translations and rotations at each node along the blade. That said, there are naturally one mode per DOF, even if these are not directly used in its solve.

Best regards,

5

Dear @Jason.Jonkman ,

Thank you very much for your previous response. As shown in the attached figure, I simulated the blade tip deflection of the 5MW reference turbine under uniform wind conditions at 11.4m/s using OpenFAST.

image
image1275×518 30.8 KB

The results exhibit a sustained and stable oscillation in the deflection values. I attempted to reproduce a similar trend using BeamDyn, but the results I obtained (as previously shared with you) differ significantly.

Could you please provide some insight into the potential reasons for the differences between the two approaches?

Thank you in advance for your time and assistance.

Best regards,

6

Dear @Min.Li,

It doesn’t sound to me like you are comparing the same thing. In your original post, you applied a 100 N force to the blade tip in BeamDyn without gravity, and in your new post, you are applying aerodynamic thrust at rated conditions to a full rotor in OpenFAST; I would expect the deflections to be quite different between these two cases.

The oscillation in the new result could be the result of shaft tilt, shear, and/or gravity, depending on the conditions you are simulating in OpenFAST.

Best regards,