Traditional intelligent fault diagnosis works well when the labeled training data (source domain) and unlabeled testing data (target domain) are drawn from the same distribution. However, in many real-world applications, the working conditions can vary between training and testing time. In this paper, we address the issues of intelligent fault diagnosis when the data at training and testing time do not come from the same distribution as a domain adaptation problem using Domain Adaptive Convolutional Neural Networks or DACNN. Our proposed DACNN consists of three parts: a source feature extractor, a target feature extractor, and a label classifier. We adopt a two-stage training process to obtain strong faultdiscriminative and domain-invariant capacity. First, we obtain fault-discriminative features by pre-training the source feature extractor with labeled source training examples to minimize the label classifier error. Then, in the domain adaptive fine-tuning stage, we train the target feature extractor to minimize the squared Maximum Mean Discrepancy (MMD) between the output of the source and target feature extractor, such that the instances sampled from the source and target domains have similar distributions after the mapping. Furthermore, to enable training efficiency in domain adaptation, the layers between the source and target feature extractors in our DACNN are partially untied during the training stage. Experiments on the bearing and gearbox fault data showed that DACNN can achieve high fault diagnosis precision and recall under different working conditions, outperforming other intelligent fault diagnosis methods. We also demonstrate the ability to visualize the learned features and the networks to better understand the reasons behind the remarkable performance of our proposed model.

Bearings, as universal components, have been widely used in the important position of rotating machinery. However, due to the distribution divergence between training data and test data caused by variable working conditions, such as different rotation speeds and load conditions, most of the fault diagnosis models built during the training stage are not applicable for the detection in the test stage. The models dramatically lead to performance degradation for fault classification. In this paper, a novel bearing fault diagnosis method, domain adaptation by using feature transfer learning (DAFTL) under variable working conditions, is proposed to solve this performance degradation issue. The dataset of normal bearings and faulty bearings are obtained via the fast Fourier transformation (FFT) of raw vibration signals, under different motor speeds and load conditions. Then, marginal and conditional distributions are reduced simultaneously between training data and test data by refining pseudo test labels based on maximum mean discrepancy (MMD) and domain invariant clustering (DIC) in a common space. Ultimately, a transferable feature representation for training data and test data is achieved.With the help of the nearest-neighbor (NN) classifier built on the transferable features, bearing faults are identified in this common space. Extensive experimental results show that DAFTL can identify the bearing fault accurately under variable working conditions and outperforms other competitive approaches.

Bearing failure is the most common failure mode in rotating machinery and can result in large financial losses or even casualties. However, complex structures around bearing and actual variable working conditions can lead to large distribution difference of vibration signal between a training set and a test set, which causes the accuracy‐dropping problem of fault diagnosis. Thus, how to improve efficiently the performance of bearing fault diagnosis under different working conditions is always a primary challenge. In this paper, a novel bearing fault diagnosis under different working conditions method is proposed based on domain adaptation using transferable features(DATF). The datasets of normal bearing and faulty bearings are obtained through the fast Fourier transformation (FFT) of raw vibration signals under different motor speeds and load conditions. Then we reduce marginal and conditional distributions simultaneously across domains based on maximum mean discrepancy (MMD) in feature space by refining pseudo test labels, which can be obtained by the nearest‐neighbor (NN) classifier built on training data, and then a robust transferable feature representation for training and test domains is achieved after several iterations. With the help of the NN classifier trained on transferable features, bearing fault categories are identified accurately in final. Extensive experiment results show that the proposed method under different working conditions can identify the bearing faults accurately and outperforms obviously competitive approaches.

Gathering experience and organizing knowledge from a large number of engineering construction projects is conducive to more effective and efficient safety risk management in construction projects. Metro construction practitioners often find it difficult to determine what professional knowledge is needed to establish better management. By constructing the knowledge structure of safety risk management, which is composed of domain knowledge entities (DKEs) and their hierarchical relations, practitioners can systematically master the knowledge of safety management, enhance safety management levels, and reduce the occurrence of accidents. Traditionally, domain knowledge structure was determined by experts, the mistakes occur due to the limitations of individual knowledge, and high time costs are unavoidable due to the massive amount of data. Therefore, in this study, we used a rule-based Chinese-language natural language processing (C-NLP) method to automatically extract the hierarchical relations between DKEs from a large dataset of unstructured text documents; we aimed to clarify the affiliation relationship and parallel relationship between DKEs. First, 68,817 sources of literature written in Chinese were collected. Next, the specific syntactic structures of relations of the DKEs were analyzed. Hierarchical extraction rules, including 16 hyponymic indicators and 8 appositive indicators, were revealed based on the linguistic characteristics. Then, the relations were extracted from test dataset. The precision and recall values were used to verify the model. Finally, the hierarchical relations of all the DKEs were extracted, and the knowledge structure was formed. The proposed method of hierarchical relation extraction contributes to the quick automatic construction of knowledge structures and minimizes expert bias. The knowledge structures can be used to guide safety training and can assist practitioners in safety risk management.

Traditional data-driven intelligent fault diagnosis methods have been successfully developed under the closed set assumption (CSA). CSA-based fault diagnosis assumes that the fault types in the test set are consistent with that in the training set, which can achieve high accuracy, but this is generally not valid in real-world industrial applications where the collection of data in industrial applications is often limited. As it is unrealistic to assume that the training set will cover all fault types, the application of the fault classifier may fail when the test set contains unknown fault types because the probability of input samples belonging to unknown types cannot be obtained. To solve the problem of how unknown fault types may be accurately identified, this paper further studies the open set assumption (OSA) fault diagnosis. We propose an open set convolutional neural network (OS-CNN) method and apply our OS-CNN model to an improved OpenMax method as a deep network to accurately detect unknown fault types. The overall performance was significantly improved as our OS-CNN model was able to effectively tighten the boundary of known classes and limit the open-space risk for the OpenMax method based on distance modeling. The overall effectiveness of the proposed method was verified by experimental studies based on four different bearing datasets. Compared with state-of-the-art OSA fault diagnosis method, our method cannot only realize the correct classification of the known fault classes, but it can also accurately detect the unknown fault classes.

Envelope analysis is a widely used method in fault diagnoses of rolling bearings. An optimal narrowband chosen for the envelope demodulation is critical to obtain high detection accuracy. To select the narrowband, the fast kurtogram (FK), which computes the kurtosis of a set of filtered signals, is introduced to detect cyclic transients in a signal, and the zone with the maximum kurtosis is the optimal frequency band. However, the kurtosis value is affected by rotating frequencies and is sensitive to large random impulses which normally occur in industrial applications. These factors weaken the performance of the FK for extracting weak fault features. To overcome these limitations, a novel feature named Order Spectrum Correlated Kurtosis (OSCK) is proposed, replacing the kurtosis index in the FK, to construct an improved kurtogram called Fast Order Spectrum Correlated Kurtogram (FOSCK). A band-pass filter is used to extract the optimal frequency band signal corresponding to the maximum OSCK. The envelope of the filtered signal is calculated using the Hilbert transform, and a low-pass filter is employed to eliminate the trend terms of the envelope. Then, the non-stationary filtered envelope is converted in the time domain into the stationary envelope in the angular domain via Computed Order Tracking (COT) to remove the effects of the speed fluctuation. The order structure of the angular domain envelope signal can then be used to determine the type of fault by identifying its characteristic order. This method offers several merits, such as fine order spectrum resolution and robustness to both random shock and heavy noise. Additionally, it can accurately locate the bearing fault resonance band within a relatively large speed fluctuation. The effectiveness of the proposed method is verified by a number of simulations and experimental bearing fault signals. The results are compared with several existing methods; the proposed method outperforms others in accurate bearing fault feature extraction under varying speed conditions.