Identification of stick-slip friction in single-degree of freedom system using the random decrement technique

The identification of modal parameters of structures in operational conditions is termed Operational Modal Analysis (OMA). Stick-slip friction is common in many structures, for example offshore oil and gas platforms. The present OMA techniques are based on the assumption of linearity, and when stick-slip friction is present in a system, it is no longer linear. This study investigates how Random Decrement (RD), which is a technique used in OMA, can be used to identify stick-slip friction in a single degree of freedom system. The RD technique can be applied in a set of triggering levels in the same response signal, to calculate RD signatures, each representing the system vibrating at different amplitudes. From RD signatures, the modal parameters can be estimated using time-domain parameter estimation methods. From the changes in modal parameters, associated with the respective amplitude level in the response signal, the nonlinearity is characterized. Two RD triggering conditions are investigated to examine the applicability in identifying the stick-slip nonlinearity. A numerical study is compared with an experimental study of a single degree of freedom system with stick-slip friction.