Abstract An integrity monitoring of integrated navigation in the presence of slowly growing errors (SGEs) is proposed. SGEs with gradual growth over time are the worst category of latent failures. Tightly coupled inertial navigation system (INS)/Global Navigation Satellite System integration is presented by taking INS errors, bias and drift of receiver clock, baro‐altitude, pseudo‐range errors and ionospheric errors into consideration. Based on the RTCA performance standards DO‐229 and DO‐384, the simplified multi‐filters solution separation is employed for fault detection and calculation of corresponding outputs. For the fault exclusion part, the authors introduce a post pseudo‐range residual and measurement averaging method that is designed to quickly and effectively address SGEs and large measurement noises. Furthermore, the authors have designed a reconstruction logic for the filters that guarantees the continuity of the civil aviation system by considering the variation of visible satellites and historical information. The simulation results demonstrate that the proposed approach satisfies the performance requirements for civil aviation of En‐route and is able to correctly exclude faults and respond quickly in the presence of different levels of SGEs and measurement noises.
In allusion to residual chi-square test method has low sensitivity for soft fault detection and cannot isolate the faulty system in integrated navigation system, a redundant INS/ADS fault detection and isolation method based on Dempster-Shafer (D-S) evidence reasoning is proposed in this paper. In this method, three INS/ADS and three INS/GPS sub-filters are constructed respectively by introducing intact GPS in the three redundancy INS/ADS system, and the difference between the residuals of each two sub-filters is used as evidence, then the fault detection of sub-filters is completed by using D-S evidence reasoning. On this basis, the fault isolation and system reconstruction methods are given, and the fault isolation of the INS/ADS integrated navigation system is realized. The simulation results show that the proposed method can not only improve the sensitivity of soft fault detection, but also isolate the fault system in integrated navigation system.
Fault diagnosis of the subway plug door plays an essential role in the safe operation of the city subway. To improve the diagnosis accuracy of the subway plug door, fault diagnosis of the plug door based on Ensemble Empirical Mode Decomposition (EEMD) and adaptive feature extraction was presented in this paper. Firstly, EEMD was used for decomposition of raw data, and the intrinsic mode function (IMF) after decomposition was selected by correlation coefficient criteria. Then, the fault features in IMFs was extracted and the sensitive features among which was selected by the sensitive index. Finally, the faults were classfied by Gray Wolf optimized Support Vector Machine (GWO-SVM). The experiment with the measured data of a subway door shows that this fault diagnosis method can adaptively extract the relative optimal characteristic quantity, identify the normal state and four different fault states effectively with the recognition accuracy of 89.35%, which is valuable in the engineering application.
Satellite selection is an effective way to overcome the challenges for the processing capability and channel limitation of the receivers due to superabundant satellites in view. The satellite selection strategies have been widely investigated to construct the subset with high accuracy but deserve further studies when applied to safety-critical applications such as the receiver autonomous integrity monitoring (RAIM) technique. In this study, the impacts of subset size on the accuracy and integrity of the subset and computation load are analyzed at first to confirm the importance of the satellite selection strategy for the RAIM process. Then the integrated performance impact of a single satellite on the current subset is evaluated according to the performance requirement of the flight phase. Subsequently, a performance-requirement-driven fast satellite selection algorithm is proposed based on the impact evaluation to construct a relatively small subset that satisfies the accuracy and integrity requirements. Comparison simulations show that the proposed algorithm can keep similar accuracy and better integrity performances than the geometric algorithm and the downdate algorithm when the subset size is fixed to 12, and can achieve an average 1.0 to 2.0 satellites smaller subset in the Lateral Navigation (LNAV) and approach procedures with vertical guidance (APV-I) horizontal requirement trial. Thus, it is suitable for real-time RAIM applications and low-cost navigation devices.
Sparse coding-inspired high-resolution inverse synthetic aperture radar (ISAR) imaging based on multistage compressive sensing (CS) is proposed in this paper. To achieve high cross-range resolution within a short coherent processing interval (CPI), we divide the ISAR imaging process into multiple stages, each of which can be regarded as sparse-coding processing, and the encoding and decoding matrices can be obtained by solving an optimization problem using the error backpropagation algorithm. The decoding matrix can be regarded as a sparse dictionary, and we can recover the ISAR image by exploiting the smoothed ${l_0}$ norm algorithm based on the decoding matrix and CS theory. The ISAR image is then transformed into a time-domain echo by the inverse fast Fourier transform, and the echo can be regarded as the input for the next stage. At each stage, the resolution is gradually improved until we obtain the expected high-resolution ISAR image. Thus, the signals' energy can be fully accumulated step by step, and we can obtain a less noise and focused ISAR image. Experimental results show that the proposed method can obtain higher quality ISAR images compared with other current techniques, and that it is an effective approach to ISAR imaging within a short CPI.
For the problem that INS/GPS/ADS integrated navigation cannot accurately isolate faults, this paper establishes the chi-square detection models of INS/GPS and INS/ADS and the least squares detection model of GPS/ADS. A new isolation method is designed using the standard residuals component, which solves the position drift problem caused by isolating faulty GPS. By analyzing the diagnostic features of each detection model, the combined precise fault isolation method is proposed. Simulation experiments which take into account faults of different sizes and different duration show that the proposed method can effectively achieve the precise fault isolation.
This paper designed a multimodal medical image visualization system using open source VTK on platform VS2008. The system can visualize CT, MR, PET and SPECT using different visualization methods, such as multi-planar reconstruction (MPR), curved planar reformation (CPR), direct volume rendering (DVR), indirect volume rendering (IVR) and maximum intensity projection (MIP). Clinical practice shows that the system has stable performance and the visualization methods which make the reading of different modal medical images more convenient. The maximum number of CT slices the system can reconstruct is more than 2 000, and the reconstruction speed and quality meet the clinical requirements.
The Tan‐Lu Fault Zone is a major fault system in eastern China, and its timing of activity has been the focus of much research. We studied a ductile segment of the Tan‐Lu Fault Zone, the Malongshan Shear Zone, which is located in the Feidong Complex (the southern part of the Zhangbaling Uplift). A dark biotite‐adamellite mylonite has been recognized in the Malongshan Shear Zone, and the mylonitic foliation strikes NNE, consistent with the regional orientation of the Tan‐Lu Fault Zone. The occurrence of abundant syn‐tectonic leucocratic veins within the biotite‐adamellite mylonite indicates that ductile shearing was accompanied by hydrothermal activity. To constrain the timing of deformation along the Malongshan Shear Zone, we dated the biotite‐adamellite mylonite and the leucocratic veins using zircon U–Pb geochronology. The weighted mean ages of zircon grains from the biotite‐adamellite mylonite (159.0 ± 5.5 Ma) and the captured Group 2 (156.3 ± 3.7 Ma and 173.2 ± 4.2 Ma) of leucocratic veins are interpreted as the ages of protoliths of the biotite‐adamellite mylonite during the Jurassic. Additional weighted mean age of the hydrothermal zircon grains (130.9 ± 3.6 Ma) represents the timing of crystallization of the veins. Therefore, the results indicate that the Malongshan Shear Zone (and hence the southern segment of the Tan‐Lu Fault Zone) was active during the Early Cretaceous (~131 Ma). Based on the present results and existing data, we consider that sinistral shearing of the Tan‐Lu Fault Zone during the Early Cretaceous was controlled by oblique subduction of the Pacific Plate at a high angle.
Ray casting algorithm is one important method to render CT volumes with 2D CT slices, and it can be accelerated using graphics hardware. In this paper, we developed an efficient volume rendering system based on ray casting using C++ and VTK, and designed common shading and classification transfer functions to highlight different organs/tissues of a CT volume. With this system we experimented CT volumes using CPU ray casting and GPU ray casting respectively, and then we did the same experiments on different graphics cards. The results showed that we can highlight the organs/tissues in which we are interested by setting proper transfer functions and that the rendering efficiency can be accelerated greatly using graphics cards with nVidia GPU GT220 or higher almost with the same visualization quality as that of CPU ray casting.
It is very important to predict the velocity accurately before drilling in the well location demonstration of seismic exploration. There are different ways to get formation velocity:borehole velocity, seismic dense point velocity (the stack velocity picked up from velocity spectrum processed at multiple locations near the pre-exploration well. In general, the time-depth relationship can be obtained by using the seismic dense point velocity near the pre-exploration well location for pre-drilling prediction. However, in the application of complex fault block in Weixi exploration area, it is found that the seismic density point velocity is greater than the wellbore VSP velocity, which leads to a greater prediction depth, which means the prediction error will be larger. It is not possible to use seismic dense point velocity for predrilling prediction. For this reason, a 3D velocity model is established based on VSP velocity and horizon constraints, and the velocity of pre-exploration well point is extracted from the velocity model to carry out time-depth conversion. The actual drilling shows that for the complex fault block structure in Weixi exploration area, the well velocity extracted by model is closer to that of actual drilling, and the prediction error is within the allowable range. For areas with complex geological and seismic characteristics, the velocity suitable for the area should be used for prediction, so as to minimize the prediction error and reduce the exploration risk.
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