Early contact detection between two components

There are several structural components in industries and plants that come in contact with adjacent components over a period of their functional use, for example, the use of coaxial tubes for carrying hot fluid through inner tube. The early detection of such contacts between two components is important for the system performance and safety considerations in many cases. The detection based on the change in the natural frequencies may not be practical in many cases as the shift in frequencies is often found to be insignificant during contact. However, they interact nonlinearly when excited either by the external aid like shaker or through their service loads. Here, the experimentally measured responses in a simple laboratory setup simulating nonlinear interaction between two components were processed to identify the feature for the early contact detection. It has been observed that the higher order coherences (Bicoherence and Tricoherence) of the responses are the most effective parameters for such contact detection, which is presented here.