A novel output-only time-domain nonlinear subspace approach for identifying vibrating structures with clearance nonlinearity

Abstract The problem of output-only identification of vibrating structures with clearance nonlinearity is considered, as clearance nonlinearity exists widely in mechanical structures and the ambient excitation is usually difficult to apply or measure under operating conditions. A novel output-only time-domain nonlinear subspace identification (OOTNSI) method is proposed in this work by separately identifying the underlying linear system of nonlinear structures based on input-output data under low-level excitation, and identifying nonlinear parameters by only using output data under high-level excitation. In case the underlying linear system is known or obtained in advance, the OOTNSI method is able to operate by exclusively using the measured displacement responses of the structure, without measuring its excitation forces. The proposed method is respectively employed for the identification of three degrees-of-freedom numerical and experimental systems with clearance nonlinearity, and comparatively assessed against the existing time-domain nonlinear subspace identification (TNSI) method. The comparisons demonstrate that the proposed OOTNSI method is capable of performing output-only identification of vibrating structures with clearance nonlinearity and can achieve similar identification accuracy as the existing TNSI method operated in an input-output manner.