Experimental evaluation of veering, crossing and lock-in occurring in parameter varying systems

The phenomena of mode veering, crossing and lock-in are experimentally analyzed in this paper. Their occurrence is generally found, under different conditions, when there is a parameter varying in the system, producing a change in its behavior. 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 a general weakly-coupled two-degrees of freedom systems and experiments, appropriately designed to highlight these phenomena, are presented. In particular, experimental evidences of the damping-dependent transition from veering to crossing is investigated in a two beam system, and experimental lock-in in brake squeal are recalled to show how in gyroscopic systems, when two coupled mechanical parts have the same eigenvalues (lock-in state), the whole system may becomes unstable. © The Society for Experimental Mechanics, Inc. 2014.