Experimental characterization of veering crossing and lock-in in simple mechanical systems

In this paper, mode veering, crossing and lock-in phenomena are experimentally analyzed and characterized. Their occurrence is generally found, under different conditions, when there is a parameter variation in the system that produces a change in its behaviour. It often happens that, when the natural frequencies of two modes approach each other, they can cross, veer and eventually present a lock-in state. The problem is analytically investigated for general weakly-coupled two-degrees of freedom systems and experiments, appropriately designed to highlight these phenomena, are presented. In particular, experimental evidence of the damping-dependent transition from veering to crossing is investigated for a two beam system, and experimental lock-in is recalled to show how the gyroscopic systems become unstable when two coupled mechanical parts have the same eigenvalue.