Recursive Method in Modal Parameter Identification of Aerospace Structures under Non-Gaussian NoiseRead the full article
Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.
Chief Editor, Dr Thai, is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.
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Linkage Analysis between Solid-Fluid Coupling and the Strength Reduction Method for Karst Cave Water Inrush in Mines
The present paper aims to study the mechanical mechanism and characteristics of water irruption from Karst cave. Combining the nonlinear seepage-pipe coupling model with the strength reduction method, the linkage analysis of fluid solid coupling and strength reduction method are constructed to study the whole process of confined Karst cave water inrush. Taking the water inrush accident of Shibaijing of the Qiyi mine in south China as an example, the instability mechanism of the water-proof rock pillar and evolution of water inrush are discussed. It is suggested that water discharge on the working face augments with the increase in the reduction factor of the water-proof rock pillar before the rock pillar loses its stability. Once the rock pillar becomes unstable, Karst water bursts from confined Karst cave in a pipe flow shape, and the water irruption quantity reaches the peak value in a short time by adopting the pipe flow to simulate and then decreases slowly. The hydraulic rough flow at the initial stage changes into pipe laminar flow finally in the process of Karst water inrush, due to the constraint of Karst cave water reserve. The conception for the safety factor of the water-proof rock pillar introduced, the relation of the safety factor, Karst cave water pressure, and thickness of the water-proof rock pillar are studied. It is proposed that thickness of the water-proof rock pillar whose safety factor equals 1.5 is regarded as the calculating safety thickness of the water-proof rock pillar, and the safety thickness of the water-proof rock pillar setting in mining engineering should be equal to the sum of the blasthole depth, blasting disturbance depth, and the calculating safety thickness. The reason leading to Karst water inrush of Qiyi Mine is that without advanced boreholes, the water-proof rock pillar is set so small that it could not possess safety margin, so the confined Karst cave water breaks the water-proof rock pillar and bursts out. Combining the solid fluid coupling theory, pipe flow theory, and strength reduction method, the nonlinear mechanical response of confined Karst cave water inrush is studied, which provides a new study method for the whole process of confined Karst cave water inrush.
Dynamic Analysis of Metro Train-Monolithic Bed Track System under Tunnel Differential Settlement
The metro tunnel lines built in a soft soil area may suffer from tunnel differential settlement due to the high compressibility of soft soil, the engineering constructions nearby tunnel lines, and the cyclic load of metro trains. In this paper, a dynamic coupling model for a metro train-monolithic bed track system under tunnel differential settlement is established. A cosine function is introduced to simulate a real settlement curve measured from a metro tunnel in southern China, and the vibration performance of the train-track system under tunnel settlements is investigated in both the time domain and frequency domain. Based on the standards for the train safety and passengers’ comfort, the speed limit for the metro train traveling on a monolithic bed track with different settlement distributions are concluded. The present research could be useful for the operation and maintenance of metro tunnels in soft soil areas.
Experimental and Numerical Studies on Vibration Modes and Transcranial Attenuation Characteristics in Unilateral Bone Conduction Hearing
Bone conduction (BC) hearing devices have been used to improve hearing in patients with unilateral conductive hearing loss; however, the clinical results of improvement in the sound localization ability are still controversial. Transcranial transmission in BC may be an important factor affecting sound localization abilities. Transcranial or interaural attenuation, derived from energy attenuation during the BC process, is determined by the different transfer functions of multiple pathways and affected by the whole-head vibration modes. The purpose of this study is to analyze the frequency dependence of BC vibration modes of the whole head, the contribution of middle and inner ear pathways to BC hearing, and the relationship between transcranial attenuation results by dynamics measurement and hearing thresholds. Experimental studies of vibration modes and transcranial attenuation characteristics in BC are performed using scanning laser Doppler vibrometry (LDV) measurements on human cadaver heads. Differences in vibration modes between the excitation and contralateral sides are observed. Additionally, a multiscale human whole-head FE model, including the skull, bony outer ear, ossicular chains, and bony inner ear structures, is proposed to study the mechanism of BC in the human hearing system. After verifying the rationality of the FE model using mechanical impedance and frequency response data, the transcranial attenuation on the temporal bone surfaces and the middle ear structure is calculated in the FE model. Moreover, the vibration characteristics of bilateral ossicular chains and the cochlear bony wall are observed in the whole-head FM model to study their contributions to BC hearing. By analyzing the experimental and numerical results of the vibration modes and the frequency response of the whole head incorporating the ossicular chain and cochlear bony wall, the intrinsic relationship between the results of transcranial attenuation by 1D LDV, 3D LDV, and hearing threshold measurements is further investigated.
An Optimized Pulse-Counting Method for Compensation Vector Calculation in the Automatic Balancer
The accuracy of the counterweight positions in an automatic balancing system deeply affects dynamic balancing. Compensation vector is synthesized by the two counterweights located in the electromagnetic dual-weight automatic balancer. Therefore, if the position of the counterweight is inaccurate, it may result in a wrong adjustment and a larger imbalance of the rotor system. In this paper, an optimized pulse counting method for compensation vector calculation in an electromagnetic dual-weight balancing system is proposed based on a programmable logic controller (PLC). A propeller automatic balancing simulation test bench is used to verify the effect of the method by obtaining the positions of the counterweights and synthesizing the compensation vector in the working mode. The error is less than 1/80 which means that it does not exceed one step in the 80-position-balancer at 1200 rpm. The proposed control system can work without computers or high-speed data acquisition equipment, which improves the stability and flexibility of the control system, facilitates the design of the automatic balancing system, and shows excellent potential for industrial applications.
Correlation Effects of Near-Field Seismic Components in Circular Metro Tunnels: A Case Study—Tehran Metro Tunnels
Seismic evaluation of underground structures such as tunnels requires nonlinear dynamic analysis, due to the complex dynamic behavior of soil and the interaction of soil and structure. Simulation of the seismic response of the structure using nonlinear dynamic analysis is possible only with proper acceleration time history. Considering the vertical component of the earthquake (such as near-fault earthquakes) on the site is an important factor to achieve real structural responses. In the current study, soil-tunnel system has been modeled in ABAQUS software, considering Mohr–Coulomb nonlinear model for soil and concrete damage plasticity model for tunnel lining. In order to investigate the effect of seismic components correlation under different combinations of loads on the acceleration, axial force, and maximum shear force in tunnel lining, nonlinear dynamic analysis has been performed under four near-field earthquakes with different horizontal and vertical component ratios, considering 15 load combinations. The results show that increasing the vertical-horizontal component ratio has an insignificant effect on the maximum horizontal acceleration experienced by the tunnel lining. Also, the results of axial forces and shear forces indicate that increasing the ratio of vertical to horizontal components of the earthquake is the most effective factor on the axial force response.
The On-Chip D-LMS Filter Design Method of Wireless Sensor Node Based on FPGA
In the real-time position technology of underground shallow source, the signal denoising performance of wireless sensor nodes directly determines the location speed and accuracy of underground burst point. Because of the complexity and randomness of the underground medium and the fact that underground explosion is a nonstationary transient process, the problems of low convergence rate and poor steady-state performance of the filter exist when the existing LMS algorithm is used for signal denoising. In light of the above concerns, this paper comes up with a signal denoising algorithm and hardware implementation method based on D-LMS (delay-LMS). Firstly, according to the autocorrelation function characteristic of random signal, using the principle that the autocorrelation function time delay characteristic of narrowband signal such as explosion vibration signal is better than that of wideband random signal such as ground noise, the D-LMS filter algorithm is constructed by introducing the time delay parameter. Secondly, the selection method of key parameters in D-LMS hardware implementation is analyzed. Thirdly, the corresponding hardware circuit is designed by FPGA, and the simulation is carried out. Numerical simulation and experimental verification show that compared with the existing LMS improved algorithm, the D-LMS algorithm proposed in this paper has higher denoising stability and better denoising effect. Compared with the signal postprocessing method based on the host computer, the signal denoising speed of this method is significantly improved. This method will provide a powerful theoretical method to solve the problem of high-precision and fast source positioning and provide technical support for the development of high-speed and real-time source positioning instruments.