1E+7 TeetSSSp - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
1.0401E+10 TeetHSSp - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
This is a part of my teeter file. I want to figure out a minimum value of SSSp. Because, firstable, i don’t consider about fatigue now. I just only want to see the decrease of load at the blade root and tower base. I calculated the c and k values by referencing other papers and used a value of about 2E+8. For reference, the model I’m using is the 22 MW turbine model. When I used that SSSp value, the loads in the x-direction at the two previously mentioned locations did not decrease; instead, they actually increased. I expected that enabling the teeter function would reduce the loads, but they did not decrease at all. Therefore, while I was trying to reduce the k value slightly, I found a strange result. When I set k below 1E+7, the OpenFAST simulation showed the teeter angle dropping rapidly to −11deg and failing to recover. Why does this happen?
If I understand correctly, you’ve modified the IEA Wind 22-MW RWT to be a 2-bladed rotor with the teeter degree of freedom enabled (NumBl = 2, TeetDOF = TRUE in ElastoDyn); is that correct? Can you share your full ROTOR-TEETER section of the ElastoDyn input file?
---------------------- ROTOR-TEETER --------------------------------------------
1 TeetMod - Rotor-teeter spring/damper model {0: none, 1: standard, 2: user-defined from routine UserTeet} (switch) [unused for 3 blades]
0.0 TeetDmpP - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
2.645E+8 TeetDmp - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
0.0 TeetCDmp - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
00.0 TeetSStP - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
11.0 TeetHStP - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
1E+7 TeetSSSp - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
1.0401E+10 TeetHSSp - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
I have an additional question. When I ran the simulation with SSSp set to 1E+4 and then to 1E+7, the loads on the blades and the tower were almost identical, and TeetDeg was exactly the same. I don’t think it’s reasonable for these results to be unchanged even though the teeter stiffness was set differently. Is there a specific reason why the analysis would produce the same values in this case?
The teeter springs and stops are symmetric about 0 degrees, so, by setting TeetHStP = 11deg, you’ve placed a hard stop at -11 and 11deg. From your simulation, it looks like the rotor keeps bouncing around the lower limit.
I would expect different teeter stiffness to result in different response.
