Journal of Vibroengineering
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Dynamic responses of loess tunnels with different cross sections under the action of earthquakes, rainwater seepage and trains
Get PDFFour tunnel models with different cross sections were established, and the models were coupled with fluid models to investigate rainwater seepage-, earthquake- and train-induced effects. The displacements, stresses and pore water pressures of key points in the loess tunnels were analyzed, and the dynamic response patterns of loess tunnels under the influence of earthquakes, rainwater seepage and train loading were obtained. The results show that the dynamic responses of loess tunnels with different cross sections vary. Although the patterns of acceleration and displacement in the four loess tunnel sections are basically identical, the peaks of acceleration and displacement are lowest in the circular tunnel and highest in the rectangular tunnel. Furthermore, obvious stress differences exist among the different sections. The stress is lowest in the circular loess tunnel, intermediate in the curved-wall and straight-walled arch tunnels, and highest in the rectangular tunnel. The pore water pressures of loess tunnels increase with increasing depth, but the differences are not large. Shaking-table testing of a curved tunnel was carried out, and the results were consistent with the numerical results
Propagation of shock wave and structure dynamic response of explosion in a subway station: a case study of Wuhan subway station
Get PDFWith the development of urbanization, the construction of the subway has been greatly developed. Meanwhile, the public concern of terrorist attacks on subway stations keeps driving the related research. In this paper, the representative subway station of Wuhan Metro Line 8, Mafangshan station, which is now under construction, is taken as a case, the dynamic finite element numerical simulation software ANSYS/LS-DYNA is employed to establish finite element model. The propagation law transmitting through the station structure and the dynamic response of the station under different TNT charges are analyzed. It is indicated that the propagation of shock wave is complicated due to the semi-closed environment of the station as well as the reflection and transmission of the stress wave in the structure. Specifically, in the station structure, the displacement of the platform plate was the largest, under the explosive action of different TNT charge, the displacement of platform plate is 13.6 mm (5 kg), 22. 8mm (10 kg), 35.2 mm (20 kg), 45.6 cm (30 kg), 68.8 cm (40 kg), respectively. The middle part of the pillar was the largest displacement on the pillar. Based on the dynamic stress response analysis of the station pillar, it shows that the maximum value of the stress value in the pillar is located at the junction of the pillar and the plate. Under the explosive action of 40 kg TNT charge, the maximum tensile stress of the junction of the pillar and the plate reached 45.1 MPa. Therefore, more attention should be paid to anti-explosion measures herein. Besides, through the analysis of the tensile stress value at the bottom of the pillar under different charge quantity, the TNT charge quantity for the crack at the bottom of the pillar is determined to be 6.77 kg by the formula fitting
Performance evaluation method of spherical bearing based on correlation and sensitivity analysis and SVM
Get PDFIn order to ensure the safety of bridge structure operation, the working mechanism and damage mechanism of spherical steel bearings commonly used in urban rail transit bridges and large highway bridges are studied. This study combines correlation and sensitivity analysis methods, and proposes that the correlation between output parameters and input parameters and the order of sensitivity are used as the basis for selecting spherical steel bearings. The sudden change of the sensitivity of each operating point is used as the basis for index division, and the discriminating system of spherical steel bearings is established accordingly. Combined with SVM, it is trained into a ball-type steel bearing safety level discrimination model. Through the test data test, the results show that the test of the discriminant model is effective
Free vibration analysis of structural-acoustic coupled system using hybrid impedance and mobility approach
Get PDFThe present paper discusses impedance and mobility approach integrated with finite element method (FEM) for free vibration analysis of structural-acoustic coupled systems for irregular geometry. In this method, coupled natural frequencies of any irregular geometry with flexible surfaces with different boundary conditions can be estimated. The proposed hybrid method helps to understand the underlying physics of structural-acoustic coupling in complex geometries. The formulation being in impedance and mobility form, gives more insight in understanding coupled modes of the complex geometries. It is for three dimensional irregular geometries, so it can be used in most of the practical applications where coupled natural frequencies play a vital role. The proposed method is demonstrated for regular and irregular geometry with one wall flexible configuration. The results are corroborated with existing literature data for regular geometry and numerical models for irregular geometry
Design and analysis of actuator system of electromagnetic shell with high-overload resistances
Get PDFThe components of an electromagnetic shell system should be able to sustain the impact of high-strength instantaneous acceleration when the system is launched. The dynamic characteristics of high overload present significant challenges in the component (electronic and mechanical) design and part assembly of a steering gear system. This paper proposes a new design strategy for the servo system of a high-overload electromagnetic projectile. First, according to the special environment index parameters of a high-overload electromagnetic shell steering system, a new anti-overload deceleration mechanism that combines a triangular thread lead screw, a shift fork, and the entire anti-high-overload mechanical structure is proposed. The transient dynamic vibration characteristics of the entire high overload are analyzed. Based on the integrated module method for complex mechanical and electrical equipment, a mathematical model of the full closed-loop electromagnetic shell actuator system is established, and its dynamic characteristics are analyzed. Finally, a prototype of the high-overload electromagnetic projectile steering system is manufactured. By testing the maximum rudder deflection angle and the frequency and step responses of the system, the dynamic characteristics of the new high-overload electromagnetic shell actuator system are verified. This study provides a new method for designing high-overload electromagnetic shell steering gears
Design of binary weighted DAC for asynchronous ADC with improved slew rate and with calibrated size of capacitors
Get PDFThis work proposed a binary-weighted Digital-to-Analog Converter (DAC), which is designed to be used in Asynchronous successive approximation register (SAR) based Analog-to-digital converters (ADCs) specifically and in other relevant operations .The design has yielded an improved slew rate, and it is less prone to noise as the size of capacitors is taken in accordance with KT/C noise calculation. For achieving all mentioned goals, and to restrict the size of DAC, within suitable dimensions charge scaling DACs are used. One more advantage of this design is its accuracy, further it does not require op-Amps for its operation. Results of statistical simulation and mathematical consideration are published which depicts the supremacy of the design. A high-resolution DAC designed for this specific purpose has to have special consideration for the effect of local mismatch, parasitic and matching of the capacitors, for that, the common-centroid approach has been followed. This design has displayed a high resolution with small unit capacitances and that too without expensive factory calibration
Study on standard response spectrum parameters of special long-period ground movements
Get PDFMultiple earthquake damages show that the long-period ground movements have an amplification effect on the dynamic response and seismic damage of long-period structures. To form an improved code design spectrum suitable for long-period ground movements, the standard response spectra consisting of four segments for near-fault pulse-like (NFPL) and far-field harmonic (FFH) ground movements are proposed. Firstly, two types of special long-period ground movements with reliable information are selected for this research. Then, the fundamental period of a single-degree-of-freedom (SDOF) system is extended to 16 s with the damping ratio of 5 %, and the seismic response spectrum and the normalized response spectrum are analyzed. Next, the normalized acceleration spectrum of long-period ground movements is calibrated to the standard response spectrum of regular variation. Finally, the parameters of standard response spectrum about long-period ground movements and the ones of the current code design spectrum are discussed. The results show that the current code design spectrum overestimates the structural seismic response in the short period under NFPL and FFH ground movements, while it underestimates the structural seismic response in the long period. The fundamental period of a SDOF system of china’s current code design spectrum should be extended to consider the influence on long-period structures acted by a long-period earthquake. Further, it accounts for the resonance effect of long-period ground movements which ensures the seismic design safety of long-period structures
Study on reversal and lateral vibration in the stepped well
Get PDFThe reversal and lateral vibration of the drill string are very complex motion and can affect the normal operation of the drill string. The movement of the drill string in the stepped well is different from the movement of the drill string in the regular well. The vibration of the drill string in the stepped well varies with the size of the wellbore and can be visually reflected by the phase speed. To find out the relationship between reversal and lateral vibration, the natural frequency of lateral vibration of the drill string was solved by using the method of energy conservation. The analysis shows that the phase speed of flexural wave in the stepped well is faster in small size wellbore than in large size wellbore. The reversal and lateral resonance is easy to happen in small size wellbore, and the reversal will excite lateral vibration. When the sum of reversal and rotational angular frequencies approaches the natural angular frequency of lateral vibration, the lateral resonance will occur
Optimization of natural frequency for hexachiral structure based on response surface method
Get PDFTo improve the resistance to vibration and reduce its structure mass, the structural dynamic properties of hexachiral structure with negative Poisson’s ratio (NPR) are investigated. The optimization function of natural frequencies parameters is established, in which the thickness of circular nodes wall and ligaments of the hexachiral structure are defined as design variable. By normalizing the weight coefficients corresponding to the natural frequencies of different orders, the multi-objective optimization problem is converted into a single objective structural optimization problem. Finally, the cell of hexachiral structure for example, by introducing the response surfaces method, the structural optimization is carried out. The numerical analysis shows that the natural frequency is greatly increased, and the vibration resistance is strengthened. The results provide technical support for the design and application of high performance materials
Tunnel surrounding rock stability prediction using improved KNN algorithm
Get PDFAccurate prediction of the stability of rock surrounding a tunnel is important in order to prevent from rock collapse or reduce the hazard to personnel and traffic caused by such incidents. In our study, a KNN algorithm based on grouped center vector is proposed, which reduces the complexity of calculation, thus improving the prediction performance of the algorithm. Then, the improved KNN algorithm was applied to the surrounding rock stability prediction of a high-speed railway tunnel, which, to our knowledge, forms the first application thereof for the prediction of surrounding rock stability. Extensive experimental results show that our proposed prediction model achieves high prediction performance in this regard. Finally, a laboratory experiment of a tunnel is conducted to evaluate whether the tunnel surrounding rock is stable or not. The experimental results matched the prediction results obtained by our proposed prediction model, which further demonstrates its effectiveness