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Considering the flexibility of gear foundations and rotational effects, a geared rotor dynamic model for thin-rimmed helical gears is established. The deformable shafts and gear foundations are modelled by Timoshenko beam elements and Mindlin-Reissner shell elements, respectively. The beam element and the shell element are connected using the ‘interfacial coupling element’. Then the modal superposition method is adopted to improve the computational efficiency. The proposed dynamic model is verified through the comparison between the simulated responses and experimental results in a published literature. Based on the proposed dynamic model, the effects of the web thickness, the rotational effects and the helix angle on the dynamic behaviors are discussed. The results show that the dynamic responses of thin-rimmed gears obtained from the traditional dynamic model and the proposed model are quite different, which emphasizes the significances of the flexible body modeling. Compared to the centrifugal stiffening and the spin softening, the gyroscopic effect has more significant effect on dynamic characteristics. The nodal diameter vibration cannot be excited due to the absence of the axial exciting force when helix angle is zero. The increase of the helix angle will lead to more significant out-of-plane vibration of the gear foundation.

Based on the loaded tooth contact analysis method, the time-varying mesh stiffness of planetary gear set considering gear crack fault are calculated. The real crack path of gear tooth is simulated based on the fracture mechanics theory. Meanwhile, an improved lumped parameter dynamic model is also established, which can effectively consider the time-varying distance between the planet gear and the transducer mounted on the fixed ring gear. The correctness of the proposed dynamic model is verified with the simulation results in literatures and also the experimental result on a planetary gear test rig. The amplitude modulations phenomenon and the frequency modulation phenomenon can be clearly observed in the simulated results. Using the proposed dynamic model, the fluctuation of the dynamic load sharing factors which considering the crack faults of gears are revealed, the result shows that the ring gear crack fault can rarely affect the dynamic load sharing among the external meshing gear pairs. The analysis in this study can help better understand the internal laws of crack fault for planetary gear set.

Conventional intelligent diagnostic model is built on the foundation that the training data and testing data are recorded under the same operating condition, which neglects the fact that the operating condition of the rotating machinery usually varies. The feature distribution of the recorded data in one operating condition may be inconsistent with the feature distribution of the recorded data in another operating condition. It is easy to cause a significant distribution discrepancy between the training data and testing data. To address this issue, an unsupervised domain adaptation approach based on a symmetric co-training framework is proposed in this study. In the proposed symmetric co-training framework, a universal feature extractor and two individual classifiers are built as the main elements. The structures of the two classifiers are symmetric and its parameters are updated in a co-training style. The parameters of the feature extractor and two classifiers are continuously updated via an adversarial training process. The cosine similarity of the predictions from two classifiers is introduced to guide the adversarial training process, which can not only minimize the distribution discrepancies between source domain data and target domain data, but also push the feature subspaces for different healthy conditions away from the class boundaries. The application of the proposed method on two sets of experimental bearing fault data validates that the proposed method can successfully address the domain shift phenomenon between the recorded data under different operating conditions.

Considering the realistic spalling morphology obtained from the fatigue experiment, a novel dynamic model for spalled gear pairs is established in this paper. Loaded tooth contact analysis method is utilized to evaluate the meshing characteristics of spalled gear pairs. In order to verify the proposed method, the mesh stiffness and contact stress obtained from the proposed method are compared with those obtained from the finite element method and the method in published literature. The mesh stiffness and the non-loaded static transmission error are imported into the geared rotor dynamic model to acquire the dynamic responses. The spectrum characteristics and statistical indicators under different spalling patterns are acquired by the proposed model. A comparison between simulation and experiment is performed to verify the proposed dynamic model. The results show that the simulated fault features agree well with that obtained from the experiment, which indicates that the proposed model is a promising tool for the fault mechanism study of gears with realistic spalling patterns.

Excavating trajectory impact the production efficiency and overall performance of excavator directly [1]. Hence, it’s of very realistic significance to obtain the optimal excavating trajectory. Based on site test data, the point of tangency of the rack pitch line of the bucket rod and the pitch circle of the crowd gear were determined as the rotating center and the dynamic model of working mechanism was derived; due to the change law of the current and voltage of the hoist motor, the excavating process sections was separated from the excavating trajectory; log spiral model was chosen as the fitting function, and according to the following three judgment rules: maximizing soil volume in bucket, rationalizing the excavating time and minimizing the energy consumption of unit mass of soil in bucket, the optimal excavating trajectory was obtained and provided basis for the operation and design of the large mining excavator [2].