Fault Detection Based on Multi-Dimensional KDE and Jensen-Shannon Divergence.

Weak fault signals, high coupling data, and unknown faults commonly exist in fault diagnosis systems, causing low detection and identification performance of fault diagnosis methods based on T2 statistics or cross entropy. This paper proposes a new fault diagnosis method based on optimal bandwidth kernel density estimation (KDE) and Jensen-Shannon (JS) divergence distribution for improved fault detection performance. KDE addresses weak signal and coupling fault detection, and JS divergence addresses unknown fault detection. Firstly, the formula and algorithm of the optimal bandwidth of multidimensional KDE are presented, and the convergence of the algorithm is proved. Secondly, the difference in JS divergence between the data is obtained based on the optimal KDE and used for fault detection. Finally, the fault diagnosis experiment based on the bearing data from Case Western Reserve University Bearing Data Center is conducted. The results show that for known faults, the proposed method has 10% and 2% higher detection rate than T2 statistics and the cross entropy method, respectively. For unknown faults, T2statistics cannot effectively detect faults, and the proposed method has approximately 15% higher detection rate than the cross entropy method. Thus, the proposed method can effectively improve the fault detection rate.

SINS/CNS/GNSS Integrated Navigation Based on an Improved Federated Sage-Husa Adaptive Filter.

Among the methods of the multi-source navigation filter, as a distributed method, the federated filter has a small calculation amount with Gaussian state noise, and it is easy to achieve global optimization. However, when the state noise is time-varying or its initial estimation is not accurate, there will be a big difference with the true value in the result of the federated filter. For the systems with time-varying noise, adaptive filter is widely used for its remarkable advantages. Therefore, this paper proposes a federated Sage-Husa adaptive filter for multi-source navigation systems with time-varying or mis-estimated state noise. Because both the federated and the adaptive principles are different in updating the covariance of the state noise, it is required to weight the two updating methods to obtain a combined method with stability and adaptability. In addition, according to the characteristics of the system, the weighting coefficient is formed by the exponential function. This federated adaptive filter is applied to the SINS/CNS/GNSS integrated navigation, and the simulation results show that this method is effective.

SINS/Landmark Integrated Navigation Based on Landmark Attitude Determination.

Based on the situation that the traditional SINS (strapdown inertial navigation system)/CNS (celestial navigation system) integrated navigation system fails to realize all-day and all-weather navigation, this paper proposes a SINS/Landmark integrated navigation method based on landmark attitude determination to solve this problem. This integrated navigation system takes SINS as the basic scheme and uses landmark navigation to correct the error of SINS. The way of the attitude determination is to use the landmark information photographed by the landmark camera to complete feature matching. The principle of the landmark navigation and the process of attitude determination are discussed, and the feasibility of landmark attitude determination is analyzed, including the orthogonality of the attitude transform matrix, as well as the influences of the factors such as quantity and geometric position of landmarks. On this basis, the paper constructs the equations of the SINS/Landmark integrated navigation system, testifies the effectiveness of landmark attitude determination on the integrated navigation by Kalman filter, and improves the navigation precision of the system.

Experimental and numerical investigation of three-dimensional shock train topology with differently oriented background waves.

To better understand the three-dimensional topology of the interaction between the shock train and the background wave, the steady and dynamic characteristics of a shock train were investigated using wind-tunnel experiments and numerical simulation. A 14° wedge placed at the bottom and sidewalls was used to generate background waves traveling in different directions. Mounting the wedge on the bottom wall at an incoming Mach number of 1.85 leads to the formation of two symmetric and two asymmetric λ-shaped shock train leading shocks (STLSs), while an incoming Mach number of 2.70 results in one symmetric and two asymmetric X-shaped STLSs. The shock train, which runs perpendicular to the background wave, is always symmetrical at an incoming Mach number of 1.85 when the wedge is mounted on the lateral wall. A flow phenomenon in which the STLS transforms from asymmetric to symmetric after undergoing rapid movement is observed at an incoming Mach number of 2.70. The mean and root-mean-square (rms) pressure profiles confirm the morphological transformation of the STLS. The dynamic properties of the shock train are analyzed by combining the STLS trajectory with the transient wall pressure. Power spectral-density analysis reveals that the frequency of pressure oscillations is independent of whether the shock train is in the same flow cross section as the background wave and depends only on the incoming Mach number and the backpressure. The three-dimensional steady-state numerical simulation reveals the mutual interference structure of the background wave and shock train.

A Fault Diagnosability Evaluation Method for Dynamic Systems Without Distribution Knowledge.

This article addresses the quantitative fault diagnosability evaluation for dynamic systems without distribution knowledge. The system dynamics in different cases are first characterized by mean vectors and covariance matrices. Then, fault detectability and isolability are defined based on the constructed characteristics. On this basis, the Mahalanobis distance (MD) is employed to propose a fault diagnosability analysis measure. Furthermore, model-based and data-driven algorithms for fault diagnosability evaluation are given according to the MD-based measure. In addition, the reliabilities of the evaluation results are considered by taking advantage of ambiguity sets of mean vectors and covariance matrices of the system dynamics. Finally, two examples are employed to verify the effectiveness of the proposed algorithms.

Decrease of self-concept in adolescent patients with mild to moderate scoliosis after conservative treatment.

STUDY DESIGN: Comparative study. OBJECTIVE: To analyze the effect of conservative treatment on self-concept in patients with mild to moderate scoliosis. SUMMARY OF BACKGROUND DATA: The choice of surgery or conservative treatment in adolescent idiopathic scoliosis is usually done on the basis of the magnitude of the initial Cobb angle in these patients. However, mental effect of the therapy choice should be considered. METHODS: Between August 2006 and December 2008, 65 patients with adolescent idiopathic scoliosis were selected for this study. Twenty-two patients with Cobb angles between 20° and 40° received conservative treatment, 18 patients with Cobb angles between 40° and 50° received conservative treatment, and 25 patients with Cobb angles between 40° and 50° received surgical treatment. All subjects were required to fill the Children's Self-Concept Scale at the beginning of the study and at the follow-up visit 1 year later. Scores on this scale were compared among the three different groups, and between the initial visit and the follow-up visit in each group. RESULTS: At the initial test, the total self-concept score was significantly higher in the group of patients with Cobb angles between 20° and 40° than in the two groups with Cobb angles between 40° and 50°. At the follow-up visit, the total self-concept score had increased significantly in the surgically treated group (Cobb angle between 40° and 50°), however, it had decreased in the two conservatively treated groups. No significant difference was seen between the two conservatively treated groups in the amount by which the self-concept score had decreased at follow-up. CONCLUSION: In terms of mental health, conservative treatment is not ideal for patients with mild to moderate scoliosis, and in particular, it is not conducive to mental health in patients with Cobb angles between 40° and 50°.