Hello fellow researchers,
I am new here and exploring the structural dynamics of wind turbines for my master’s thesis. (I do not have structural background though).
Right now I have developed a Matlab code to find out the natural frequencies of the whole rotor from scratch and I aim to develop the same routine for openFOAM based simulation(High fidelity, inclding gyroscopic damping, gravitational and rotational stiffness.
So I am stuck at finding the regressive, collective and progressive frequencies (for flapwise, edgewise). I have developed a mass and stiffness matrix but I only get one frequency for all modes (e.g. 1 for 1st flap, 1 for 1st edge, 1 for 1st span, 1 for 2nd flap, and so on…) when I simply find eigenfrequencies using those matrices.
How to find the regressive, progressive and collective frequencies of rotor? I am not even sure if the frequencies I have are of what type of all three above. Would be helpful if I get the theory behind that.
Thanks!
Dear @Kishan.Gajjar,
Have you expressed the blade degrees of freedom in the fixed frame of reference (not rotating with the spinning rotor), e.g., by applying multi-blade coordinate (MBC) transformation? Performing the eigenanalysis in the fixed frame of reference should result in collective, progressive, and regressive modes of the rotor for each blade degree of freedom. See, e.g., the following paper by Gunjit Bir of NREL for more information: https://www.nrel.gov/docs/fy08osti/42553.pdf.
Best regards,
Dear Jason sir,
I need to get the values of rotor in-plane ,out-of-plane displacements with respect to the rotor reference frame. I am interested to know if it has some relation with the collective, progressive, and regressive modes of the rotor. Also, I had asked previously about the natural frequencies of blade flap-wise and edge-wise modes. I would like to know if there exist a combined blade edgewise and flapwise frequency for the rotor considering the dynamics of all three blades. Please excuse me if my doubt is trivial. Can you share some insight. Thanks in advance.
Best regards
Dear @Nitin.Sivakumar,
You can output from OpenFAST the tip displacements of each blade in the out-of-plane and in-plane directions, from either the ElastoDyn or BeamDyn modules (depending on which you are using to model the blade structural dynamics).
When expressing the blade flapwise or edgewise natural frequencies in the fixed frame of reference, the natural frequencies are typically expressed in terms of rotor modes, with distinct collective, progressive, and regressive natural frequencies. You can compute these via an OpenFAST linearization analysis, followed by MBC and Eigenanalysis, as has been discussed in many other forum topics.
Best regards,