Research on friction state monitoring method of liquid film seal during start-up based on acoustic emission

•A signal processing method based on singular value decompositions and adaptive variational mode decomposition (SVD-AVMD) was proposed.•AE mechanism of liquid film seal was studied based on the strength theory of shear strain energy and CEB contact model.•Liquid film seal friction experiment based on acoustic emission technology was designed.•Convolution neural network was applied to identify the friction state of liquid film seal.