I have obtained displacement time history of a sytem using ODE15i. I need to obtain FFT curve of this response. As ODE solvers use adaptive algorithm, the time interval between steps is not constant. I have tried both hanning windowing option and zero padding, but not successful. It is giving broad spectrum instead of peaks at certain frequencies. I tried NUFFT command too, but it doesn't seem to help it out. If I fix the time step while solving ODE, then only I get good FFT curve. I guess, It is not good option to fix the time step in adaptive algorithms. Here, I am attaching the code and the data for your reference which contain both fixed step and variable step data.
Kindly suggest what should be done in this scenario. Thank you.