Dear @Jason.Jonkman ,
Thank you for your prompt responses. Regarding (2), the azimuth and shaft coordinate systems follow the right-hand rule, as shown in the figure below. Nominally, e1 (c1) points downwind, and e2 points vertically upward when c3 is directed vertically upward. That is, in this case, q(TrDr) + q(GeAz) = 270 (deg) in the transformation matrix. The coordinate system definitions are found on pages 3-4 of the “FAST Coordinate Systems document”. Can this be understood in this way?
Best regards,
Dear Jason,
Thank for your prompt reply!
Best Regards,
Nikos
Dear @Yangyang.Li,
Actually, c is the shaft coordinate system (that doesn’t spin) and e is the azimuth coordinate system (that spins with the shaft) and e2 = c2 and e3 = c3 when q(DrTr) + q(GeAz) = 0.
Best regards,
Dear @Jason.Jonkman ,
Thank you for your prompt responses. I sincerely apologize for the typos in the two coordinate system diagrams. I have revised the expressions for the two coordinate systems, as shown in the figure below. Based on the mapping relationship between the LSS loads and the coordinate axes here, are they correct?
Best regards,
Dear @Yangyang.Li,
I agree with your equation relating the c (shaft) and e (azimuth) coordinate systems and agree with your figure when q(DrTr) + q(GeAz) = 270deg.
Best regards,
Dear @Jason.Jonkman ,
Based on the equations of motion developed on page 43 of the FASTKinetics document https://openfast.readthedocs.io/en/main/source/user/elastodyn/index.html, I have the following questions about the ElastoDyn module input file for Test #25: NREL 5.0 MW Baseline Wind Turbine with OC4-DeepCwind Semi, and I would like to confirm whether my understanding is correct.
- The platform equations of motion are formulated about the platform centroid (PtfmCMzt = −8.6588 m), not the platform reference point (PtfmRefzt = 0 m); the moment of inertia (I) is computed about the platform centroid and does not vary in time with platform rotation.
- When PtfmRefzt = 0, it means that: 1) The position of the inertial reference frame is at the mean sea level (MSL); more precisely, the origin of this coordinate system is located at the intersection of the mean sea level and the undeformed tower centerline, and 2)The platform’s three translational motions (surge, sway, heave) and three rotational motions (roll, pitch, yaw) are defined and can be output at this location. A detailed description of the inertial reference frame can be found on page 8 of the FAST User’s Guide.
- In the ElastoDyn module input file, PtfmCMzt = -8.6588 (≠ 13.46 m), PtfmPIner = 2.56193E+09 (≠ 6.827E+9 kg·m²), and PtfmYIner = 4.24265E+09 (≠ 1.226E+10 kg·m²). The values in parentheses (preceded by “≠”) correspond to those listed in Table 3-3 on page 9 of the document Definition of the Semi-submersible Floating System for Phase II of OC4. This discrepancy arises because the ED input file specifies only the structural properties of the platform itself, whereas the definition document includes the structural properties of the entire wind turbine system—that is, the tower, rotor-nacelle assembly, mooring system, and platform.
Best regards,
Dear @Jason.Jonkman
OpenFAST neglects these actuation loads as specified in Section 7.3.4 of IEC 61400-1 (Edition 4.0, 2019), according to the equations of motion presented on page 43 of the FASTKinetics document. The file link is provided below: https://openfast.readthedocs.io/en/main/source/user/elastodyn/index.html
If this understanding is incorrect, please kindly point it out.
Best regards,
Dear @Yangyang.Li,
I disagree. OpenFAST directly considers the influence of pitch, torque, yaw, and braking on the turbine response and loads. And any mechanical components can be considered in a post-processing step.
FYI: Blade-pitch actuator dynamics are being released soon in OpenFAST: Blade pitch dynamics and actuation by luwang00 · Pull Request #3039 · OpenFAST/openfast · GitHub.
Best regards,
Dear @Jason.Jonkman
Thank you for your prompt responses. With regard to the issue of actuation loads, I further illustrate it by taking the tower-top loads (T^tower_top) as an example, referring to page 35 of the FASTLoads file (4.9. ElastoDyn Users Guide and Theory Manual — OpenFAST v4.1.2 documentation). The explanation below is given separately for power-generating and shutdown operating conditions. The numerical values provided are purely hypothetical, and the external moments are assumed to consist only of the three moments listed below, with all other external moments, such as those due to friction, damping, and inertia, neglected. The details are as follows. If the understanding presented below is incorrect, please kindly correct it.
- Power-generating condition. In this case, the generator high-speed shaft is subjected to an external moment transmitted from the aerodynamic loads (T^aero = 10 KN•m), while the generator torque (T^gen = 4 KN•m) is balanced by the high-speed shaft brake torque (T^brake = 6 KN•m). Under this condition, the tower-top moment is T^tower_top = T^aero = 10 KN•m. Alternatively, the tower-top moment can be computed as T^tower_top = T^gen + T^brake = 10 KN•m, expressed in the form of braking torque. The specific points of application of each moment are shown in the figure below.
- Shutdown condition. In this case, T^aero = 7 KN•m, while T^gen = 0 KN•m and T^brake = 7 KN•m. However, the tower-top moment still satisfies T^tower_top = T^aero = 7 KN•m. Alternatively, the tower-top moment can be calculated as T^tower_top = T^gen + T^brake = 7 KN•m, expressed in the form of braking torque. The specific points of application of each moment are shown in the figure below.
Best regards,
Dear @Yangyang.Li,
I generally agree with your explanation.
Best regards,
