Journal of Vibroengineering
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Non-reflecting boundary used for simulating ground born vibrations caused by the moving train loads
Get PDFIn the very early the problem of train induced ground vibrations has received considerable attention, due to the sever effect of wheel-rail interaction force on the railway infrastructures and nearby buildings. To predicate and mitigate such vibration problems, three dimensional finite element packages are most recently and widely used numerical method, although method of achieving non-reflecting boundary condition to avoid the boundary-related wave reflection is still problem. In most case, wide finite element models far from the field that is capable of minimizing the reflection is favored by researchers. However, modelling wide finite element mesh is time consuming and it is the most difficult issue to determine whether the cross-sectional model is sufficient. Thus, other schemes such as the material property of the non-reflecting soil model have to incorporate to minimize the size in the cross-sectional directions. Hence, a parametric study by using ABAQUS is conducted in this paper to identify the paramount important parameters of the soil that may affect the boundary-related wave reflection caused by the moving train loads. With this perspective, the finite element model is divided into two regions, called the near-field and far-field. The near-field includes the moving train loads and other geometric/material properties of the entire railway infrastructure represented by the finite element, while the far-field is covered the non-reflecting model placed at the truncated boundaries. To this end, a systematic study is carried out to examine the sensitivity of damping ratio, length, Young’s modulus and Poisson’s ratio of the boundary in suppressing the reflections. The results demonstrate the beneficial role of the boundaries and their parameters in suppressing the reflection, if the paramount important parameters are properly selected
Method and device to investigate the behavior of large rotors under continuously adjustable foundation stiffness
Get PDFVibration problems have been observed after the installation of large rotating machines, such as electric machines and generators and paper machine rolls. One possible cause can be differences between the foundation stiffness of the installation location and the testing platform where the machine is balanced and optimized. Foundation stiffness exerts a significant effect on the behavior of a rotating system, and the above-mentioned differences can cause major unexpected changes at natural frequencies, and thus resonance. The problem is typical for large machines due to their large mass, which leads to low natural frequencies. This induces situations where these natural frequencies coincide with rotor excitations and cause excessive vibration. This study presents a novel method and a device for adjusting the foundation stiffness of a large rotor system, consequently enabling the investigation of the effect of foundation stiffness on rotor behavior. However, this investigation is restricted to the horizontal axis. The characteristics of the device were analyzed together with a rotor behavior measurement that consisted of versatile measurements of acceleration, force and displacement in different locations inside the rotating system. The device in the presented form is best applied in R&D laboratories and factory acceptance test cells, in which it can be used to predict the behavior of various rotors on different foundations. With the dynamic rotor behavior measurement performed with the device, the natural frequencies and their harmonic components can be presented as a function of foundation stiffness. This information can be used both to optimize rotor behavior in an installation location and also to improve the rotor system behavior in the design phase. The method and device presented in this study can be considered effective and successful, since the natural frequencies of the first two rotor modes could be manipulated freely at a range of 50-100 % by changing the stiffness
A road quality classification technique based on vehicle system responses with experimental validation
Get PDFAiming at estimating the road surface condition with improvement of the accuracy in spatial, this paper proposes a new method to classify road surface condition by considering identification interval based on vehicle system responses. First, the response signals in different vehicle speeds are decomposed by using both Wavelet Transform (WT) and Empirical Mode Decomposition (EMD) techniques. Then characteristics of the signals in both the time and decomposed frequency domain are subsequently extracted. An Improved Distance Evaluation Technique (IDET) is used to select superior features from the characteristics. Finally, a Support Vector Machine (SVM) classifier is applied to determine the road classification. The influences of identification intervals in spatial accuracy are discussed, and an adaptive classification interval was proposed to improve accuracy. The algorithm is validated by using both simulation and experimental results
Simulation method of impact load for vehicle drivetrain on durability test rig
Get PDFFatigue and durability tests are important to develop or to optimize the vehicle drivetrain system. Using the vehicle drivetrain road load simulation test rig to reproduce the longitudinal driving load of the vehicle on the real road and the vertical impact load caused when the vehicle is on a bumpy pavement. In order to improve the control accuracy and convergence speed, an iterative learning control (ILC) method is presented. After 10 times of learning, the control error of iterative learning control method is 4.8 %, it is better than the 7.1 % error achieved by proportional-integral-derivative (PID) control. The simulation results demonstrate that the ILC can improve the convergence rate and increase the tracking accuracy than the PID control method
Unsteady aerodynamic identification based on recurrent neural networks
Get PDFThe dynamic stall at high angle of attack is an important aerodynamic problem faced by aircraft, and it has always been a hotspot of aerodynamic research. The traditional reduced order model (ROM) methods needs to establish an accurate model, and has a high demand for experience. In this paper, a novel nonlinear aerodynamic identification method based on recurrent neural networks (RNNs) is proposed. The computational fluid dynamics (CFD) method is used to calculate the unsteady aerodynamic parameters of the NACA0012 airfoil. A group of sinusoidal chirp signals with variable amplitude and frequency are adopted as the excitation signals, and the obtained data are used to train the recurrent neural networks, and the ROM of the nonlinear aerodynamic model of high angle of attack dynamic stall is obtained. Finally, the aerodynamic parameters of a group of composite sinusoidal motion signals different from the training signals are predicted by the trained neural networks model and compared with the CFD results
Experimental study on the shear stiffness and damping ratio of the coarse-grained soil against geogrid interface
Get PDFGeosynthetic-reinforced soil structures are mostly used to retain subgrade slope of highway and railway. For the design and performance analyses of geosynthetic-reinforced soil structures under repeated loading, such as those induced by compaction, traffic and earthquakes, the understanding of cyclic soil–geosynthetic interface behaviour is of great interest. Nevertheless, experimental data concerning this type of behaviour are very scarce. A laboratory study was carried out and is described in this paper. This paper presents the behaviour of an interface between a coarse-grained soil and a geogrid under cyclic loading conditions. A large-scale direct shear test device able to perform displacement-controlled cyclic tests was used. The results obtained are presented and discussed, especially the effects of the displacement amplitude and normal stress on the shear stiffness and damping ratio are investigated. The dynamic response parameters of the soil-geosynthetic interface are greatly affected by the number of cycles, and the variations in the two parameters with the number of cycles are related to the normal stress and the shear displacement amplitude. when at large displacements, the damping ratio decreases first and then stabilizes with the number of cycles. However, at small displacement, the shear stiffness and damping ratio are all decrease somewhat at the initial stage of cyclic shearing. As the experimental materials used in this study are relatively single, and further experimental research should be carried out in the future. The shear parameters of interface in this study can provide reference for the design of reinforced soil structure
The seismically induced failure sequence of multiple components of high-speed railway bridges under different earthquake intensities
Get PDFThough seismic vulnerability analysis of highway bridges is mature, there is little corresponding research on high-speed railway (HSR) bridges. The seismic vulnerability analysis of HSR bridges is very different to and more difficult than for highway bridges because the multiple components of the track structure are very complex. To fill this research gap, the authors establish a finite element (FE) model of an HSR bridge with the China railway track system II (CRTS II), which includes sliding layers, cement asphalt (CA) layers and fasteners, base plates, track plates and rails. Analytical results show that seismic responses of multiple bridge components have a linear correlation. Thus, the overall track-bridge system can be assumed to operate like a serial system. Here, the seismic response and vulnerability of various bridge components are first analyzed using the incremental dynamic analysis (IDA) method. Afterwards, the failure sequence is found by comparing the seismic vulnerability of critical bridge components. Finally, the seismic vulnerability of the overall track-bridge system is evaluated according to the upper and lower first-bounds. Results illustrate that the system vulnerability of HSR bridges, which is very different to that of highway bridges, is mainly determined by the sliding layers and fixed bearings. In particular, the serious damage of a sliding layer is caused by the uncoordinated deformation of beam ends, and fixed bearings may break down when they are exposed to strong earthquakes. The overall track-bridge system is prone to severe seismic damage when peak ground acceleration (PGA) is larger than 0.2 g
Designing of a high speed, compact and low power, balanced-input balanced-output preamplifier latch based comparator
Get PDFAnalog and digital converters (ADCs) are the most inevitable part of today’s high-speed human interacted devices. Continuous efforts are being made to improve their performance. Despite working for the improvement of whole ADC, efforts to improve sub-modules are also significant. Comparators are also a vital part of ADC. In this work, we have proposed a novel high-speed Balanced-Input Balanced-Output (BIBO) preamplifier latch based comparator design, to be used for the designing of an Asynchronous Successive Approximation Resister (SAR) ADC. In order to make comparison faster, we have employed Preamplifier-Latch based comparator. Transistor fingering is used to save area and makes large transistor easy to handle without changing their aspect ratio. We have implemented this latch using two back to back connected inverters. These inverters are farming a positive feedback arrangement that also prohibits the comparator from bursting into the oscillation. Latch circuit uses three non-overlapping phases namely phi1, phi2 and phi3 and dissipates less power when operated on a single 1V supply voltage. All these features collectively made this comparator expedient and obtained results confirm that it can be used effectively for the designing of SAR ADC
Performance-based seismic isolation design using the theory of spatially concave friction distribution
Get PDFSeismic isolation devices were designed to protect three similar building structures, containing different objects with different fragilities, in a strong earthquake region. And a performance-based assessment framework, established by the PEER, was used to identify the seismic isolation efficiency of these devices. It optimized the ratios of spring part, viscous damping part and friction part in the seismic isolation devices, aiming at different functional buildings. Results show that a spatially concave friction distribution, combined with a weak spring, not only can reduce the structural acceleration response during earthquakes, but also decrease the structural residual displacement after earthquakes. Moreover, the spatially concave friction distribution can dissipate earthquake energy, but cannot hinder the recentering of structure like that of general uniform friction distributions. Consequently, the spatially concave friction distribution can partly or fully replace the viscous dampers, which are more expensive and short-lived. The reasonable combination of different components in the seismic isolation devices can satisfy different seismic requirements, aiming at different functional buildings
