In practical engineering applications, the vibration signals collected by sensors often contain outliers, resulting in the separation accuracy of source signals from the observed signals being seriously affected. The mixing matrix estimation is crucial to the underdetermined blind source separation (UBSS), determining the accuracy level of the source signals recovery. Therefore, a two-stage clustering method is proposed by combining hierarchical clustering and K-means to improve the reliability of the estimated mixing matrix in this paper. The proposed method is used to solve the two major problems in the K-means algorithm: the random selection of initial cluster centers and the sensitivity of the algorithm to outliers. Firstly, the observed signals are clustered by hierarchical clustering to get the cluster centers. Secondly, the cosine distance is used to eliminate the outliers deviating from cluster centers. Then, the initial cluster centers are obtained by calculating the mean value of each remaining cluster. Finally, the mixing matrix is estimated with the improved K-means, and the sources are recovered using the least square method. Simulation and the reciprocating compressor fault experiments demonstrate the effectiveness of the proposed method.

The accuracy and stability of the envelope estimation function are enduring issues throughout the research process of LMD. This paper presents double interpolation and mutation interval reconstruction local mean decomposition (DIMIRLMD) to improve the stability of the demodulation process and the accuracy of PF components. DIMIRLMD first proposes a mutation interval reconstruction envelope algorithm using extreme symmetry points to suppress the demodulation mutation phenomenon, which disturbs the stability of the demodulation process, and then selects the optimal PF component from a double interpolation PF component library based on the index of orthogonality (IO) for a better hierarchical property. DIMIRLMD was employed to analyze the simulation signal and vibration signal of a reciprocating compressor in an oversized bearing clearance state, and the results illustrate its performances are more excellent than those of three other LMD methods. Furthermore, the envelope frequency spectrum obtained from the proposed LMD presents a clear double rotation fault frequency and lower noise disturbance.

Abstract-The electromagnetic component expressions of transient electromagnetic field in formation media for ground magnetic dipole are derived based on electromagnetic field theory. Fast Hankel transform and the Gaver-Stehfest inverse Laplace transform method is used for forward numerical calculation of transient electromagnetic field in a uniform earth and layered medium. The regularity and characteristics of surface-hole transient electromagnetic method response was analyzed base on forward simulations in different conditions. The result shows that, the surfacehole TEM magnetic induction response sign change occur if borehole located farther offset distance, the status of signchange would alter in different time channel and different offset distance conditions, the induced electromotive force response can directly reflect the changes of induced eddy current field in formation medium, there is obvious difference in the electromagnetic response strength and attenuation characteristics for different electrical formation media, the difference can be used as the basis of inference layered ground dielectric structure.

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