Hi all. It's been a few years since I've posted here, but it's remained a great go-to resource for me. Any time I have dealt with mechanical vibrations, the fundamental frequency was based on a constant stiffness. However, I have never encountered the subject of finding the fundamental frequency of objects where the stiffness varies with displacement from equilibrium (i.e., a simply supported beam resting on curved supports, such that the supported length changes as the beam deflects.) Could someone point to a resource that deals with this subject? Much appreciated.