1 Introduction
1.1 Literature review
1.1.1 Model-based approach
Categories | References | Sub-categories |
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Model-based | KF-based | |
IMM-based | ||
RBPF-based | ||
RLS-based | ||
Others | ||
Data-based | SM-based | |
ML-based | ||
HM-based | ||
Wu et al. [43] | DL-based |
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High modeling difficulty. Vehicle dynamics models are challenging to be accurately built, mainly due to two causes [8]: (1) Train suspension systems are often nonlinear, and it is usually extremely difficult to obtain the detailed and accurate parameters of the nonlinear elements, such as dampers, and springs; (2) In train dynamics simulation, it is difficult to consider the elasticity of the carbody, bogie, wheelset, etc.
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High hardware cost. The above model-based approaches all require the use of a relatively large number of sensors, which makes the hardware used in RVSFD rather expensive and raises concerns about the reliability of the transducers. For instance, the minimum number of sensors used in [24] is 3, and more in [28].
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Low computing efficiency. Dynamics simulation involves a large number of nonlinear force calculations and iterative computations, especially when a complicated vehicle–track coupling system needs to be considered, resulting in low calculation efficiency.
1.1.2 Data-driven approach
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Database establishment. No matter from the perspective of data statistics or from the perspective of model training, data-driven approaches require a massive amount of historical tracking data, which is a common problem facing the entire industry.
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Development of adaptive fault feature extraction method. As far as ML-based approaches are concerned, the first step is to extract features that reflect the fault status of vehicle suspension systems. In reality, the vehicle suspension systems have many nonlinear components [44‐47], including springs, dampers, etc. The nonlinear factors of the vehicle components, usually, result in acquired signals that contain multiple natural oscillation modes, especially when multi-faults are coupled together [3]. As a result, it is difficult to characterize these nonlinear signals by using traditional single time-domain or frequency-domain feature extraction methods [48‐51].
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High sensitivity of collected signals to track irregularities and wheel wear. The running of a vehicle on a track is achieved through the wheel–rail contact. Track irregularities will seriously affect wheel–rail contact, such as contact area, contact force, and affect the vibration signals used for condition monitoring [52]. More importantly, the wheel profile will continuously change as the mileage increases due to the presence of wear [53, 54], which will seriously affect the vibration signals. In short, the high sensitivity of the collected signals to track irregularities and wheel wear could affect the robustness of data-driven approaches.
1.2 Motivation
1.3 Contribution and structure of this paper
2 Vehicle–track coupled model
2.1 Vehicle–track model
Parameter | Value | Unit |
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Fastener stiffness (lateral \(k_{{{\text{f}}y}}\), vertical \(k_{{{\text{fz}}}}\)) | 30,000, 1,50,000 | kN/m |
Cement–asphalt mortar stiffness (lateral \(k_{{{\text{b}}y}}\), vertical \(k_{{{\text{b}}z}}\)) | 70,000, 1,40,000 | kN/m |
Fastener damping (lateral \(c_{{{\text{f}}y}}\), vertical \(c_{{{\text{f}}z}}\)) | 150, 100 | kNs/m |
Cement–asphalt mortar damping (lateral \(c_{{{\text{b}}y}}\), vertical \(c_{{{\text{b}}z}}\)) | 350, 1,400 | kNs/m |
Wheel–rail contact damping | 100 | kNs/m |
Wheel–rail contact algorithm | Hertzian + FASTSIM | – |
Wheel–rail friction coefficient | 0.35 | – |
Poisson ratio | 0.28 | – |
Rail cant | 1:40 | |
Rail profile | CHN60 | – |
2.2 Track irregularities and wheel profiles
2.2.1 Track irregularities
2.2.2 Wheel wear
3 Diagnostic network design
3.1 Design of deep neural network
3.1.1 One-dimensional CNN (1DCNN)
3.1.2 The Architecture of the designed 1DCNN
3.2 Two strategies for increasing robustness against track irregularities and wheel wear
3.2.1 Gaussian white noise strategy against track irregularities
3.2.2 Edge sample training strategy against wheel wear
3.3 Diagnostic network of railway vehicle suspension systems
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Phase I Data preprocessing. In this phase, firstly, the bogie frame accelerations concerning different faults are collected, and the GWN-strategy described in Sect. 3.2.1 is then applied to the original acceleration signals.
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Phase II Training dataset establishment. Based on the ETS-strategy described in Sect. 3.2.2, the samples corresponding to the new wheel profile (S1002CN) and the samples corresponding to the most worn wheel profile (S1002CN-W190K) are chosen as the training dataset for the diagnostic network, and their upper envelopes are extracted.
4 Simulation
4.1 Case I (same line and same wheel profile)
Case | Training dataset and the number of trained samples (normal, LDF, YDF, Y&LDF) | Testing dataset and the number of tested samples (normal, LDF, YDF, Y&LDF) |
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I | WG-line: 864, 864, 864, 864 | WG-line: 352, 352, 352, 352 |
II | WG-line: 864, 864, 864, 864 | ZX-line: 1,248, 1,248, 1,248, 1,248 JJ-line: 1,248, 1,248, 1,248, 1,248 |
III | WG-line: 864, 864, 864, 864 | WG-line: 352, 352, 352, 352 |
IV | WG-line: 864, 864, 864, 864 | ZX-line: 1,248, 1,248, 1248, 1248 JJ-line: 1,248, 1,248, 1,248, 1,248 |