Cosine window-based boundary processing method for EMD and its application in rubbing fault diagnosis

A troublesome problem in application of empirical mode decomposition (EMD) method is boundary distortion. A novel boundary processing method based on cosine window is proposed here to solve this problem. With this method, a cosine window is firstly defined that its values equal to 1 in middle of the window and reduced by cosine/sine functions in both ends. Secondly, the analyzed signal is preprocessed by multiplying with the defined window, so that the amplitudes of the signal remain in middle and reduce in both ends. Lastly, EMD method is used to analyze the preprocessed signal. With the proposed method, the boundary distortion can be controlled in ends of the signal and the middle component can be correctly decomposed. Simulative and experimental studies verified that the proposed method can enormously decrease the boundary distortion of EMD and is useful in rubbing fault diagnosis of rotor system. The application in fault diagnosis of a practical machine set shows that the proposed method has strong practicability.