Journal of Vibroengineering
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Modal parameter identification of a three-storey structure using frequency domain techniques FDD and EFDD and time domain technique SSI: experimental studies and simulations
Get PDFThe aim of this study is to modal parameter identification of a three-storey structure using operational modal analysis. In this research, available techniques in both time domain and frequency domain have been utilized. In time domain, the Stochastic Subspace Identification (SSI) technique, and in the frequency domain, Frequency Domain Decomposition (FDD) and Extended Frequency Domain Decomposition (EFDD) have been used. The modal parameters of a three-storey structure have been calculated using both experimental and finite element method. For this purpose, first, the three-storey structure was modeled in the ANSYS software and then, using the vibration analysis, structural responses are determined. The structure responses are used as inputs of the operational modal analysis algorithms and the modal parameters are obtained. Then, by constructing and exciting the structure by a variety of external excitation, the responses are measured and then, they are used as inputs to the operational modal analysis algorithm to obtain the modal parameters. Since the input signal in OMA method should be random, random, periodic random, pseudo-random, and burst random signals are used for exciting the structure. Finally, the calculated modal parameters from the finite element method and empirical method are compared with each other
Dynamic response and limit analysis of buried high-pressure gas pipeline under blasting load based on the Hamilton principle
Get PDFFor non-conservative systems consisting of elastic-plastic material, dissipative damping of a system in a dynamic environment involves two parts: (1) the dissipative energy related to the velocity of the mass point and (2) the dissipative energy associated with the strain rate. In this paper, the dynamic response of buried high-pressure gas pipeline under blasting load is studied, where, dissipation of energy is explicitly considered. The dissipative work was introduced into the Lagrange function. According to the Hamilton principle and finite element theory, a non-conservative explosion model composed of elastic and plastic materials was established to identify the dynamic response and the propagation characteristics of a detonation wave in the earth medium, where the explosion cavity with a triangle pressure time history on internal wall was used to describe the explosive stress from blasting buried gas pipeline. In the scheme of modeling, 15 cases of different explosive payloads, different distances from the explosion center and different wall thicknesses of the pipe were regarded as the generalized load were carried out. Then the specific dynamic responses of pipeline under blasting load were shown in the post processing, as well as the relationship between peak particle vibration velocity and explosion distance and payload. Using three types of limit analysis methods, the critical explosive loading, critical blasting center distance and critical wall thickness of a buried high-pressure gas pipeline under blasting loading were determined. The computational method and results in this paper could be referenced for security operation of a buried pipeline and blasting construction scheme
Evaluation of brick infill walls under in-plane and out-of-plane loading
Get PDFIn this paper, the in-plane (IP) and out-of-plane (OP) interaction of masonry infill walls with various length-to-height ratios and vertical forces from dead and live loads are studied. For this purpose, calibrated numerical simulation for IP and OP behaviors of infilled frames has been exploited. In this method, first, the vertical loads are applied, then increasing IP displacement is imposed at the top of the models and finally OP demands are applied to the walls up to their failure. Two different methods of applying OP loading are studied: increasing static uniform pressure on the wall, and increasing dynamic acceleration. Three levels of IP displacement demands are considered: at the first reduction of tangential stiffness for IP force-displacement response, at the maximum IP strength, and at the displacement related to 20 % reduction of IP strength. The results obviously show that up to the point of the maximum IP strength capacity, the OP behavior of the considered models slightly enhanced due to the effects of improved arching actions originated from the development of IP compressive diagonal struts. Moreover, slight differences exist between the static and dynamic loadings in OP direction, hence proving the accuracy of the equivalent static loading in determining OP capacity for the studied infilled frames. Comparing the results of masonry infilled frames with those of the corresponding masonry walls indicate that the IP displacements negatively affect the OP strength in the latter, even at small IP displacement demands; however, the rate of OP strength reduction in larger IP drift ratios is lower compared to that of the corresponding infilled frame
The influence of water immersion on the mechanical property of cement asphalt mortar and its implications on the slab track
Get PDFDynamic compression test of cement asphalt (CA) mortar specimens, due to water immersion history of 0d, 7d, 14d and 30d, are carried out using a universal electronic test machine, with the strain rates ranging from 1×10-5 s-1 to 1×10-2 s-1. The stress-strain full curves, the compressive strength and the elastic modulus of CA mortar at different strain rates and water immersion durations are analyzed and the effects of strain rates and water immersion duration on these behaviors are studied. Experimental results demonstrate that the compressive strength and elastic modulus increase with the strain rate. In the same strain rate, the compressive strength decreases with the increase of water immersion duration, but the elastic modulus decrease first and then increase with the increase of water immersion duration. The largest reduction of average compressive strength of CA mortar is 46.5 %, and the largest reduction in the average elastic modulus of CA mortar is 47.5 %. A vertical coupling vibration model for a vehicle-railway track-subgrade system was established on the base of wheel-rail coupling dynamics theory and experimental results. The effects of elastic modulus deterioration of CA mortar on the dynamic responses of the vehicle and railway track system were studied. The results show that the reduction of CA mortar has little influence on the dynamic properties of the track and the running stability
Fault diagnosis of rotating machinery based on time-frequency decomposition and envelope spectrum analysis
Get PDFIn order to raise the working reliability of rotating machinery in real applications and reduce the loss caused by unintended breakdowns, a new method based on improved ensemble empirical mode decomposition (EEMD) and envelope spectrum analysis is proposed for fault diagnosis in this paper. First, the collected vibration signals are decomposed into a series of intrinsic mode functions (IMFs) by the improved EEMD (IEEMD). Then, the envelope spectrums of the selected decompositions of IEEMD are analyzed to calculate the energy values within the frequency bands around speed and bearing fault characteristic frequencies (CDFs) as features for fault diagnosis based on support vector machine (SVM). Experiments are carried out to test the effectiveness of the proposed method. Experimental results show that the proposed method can effectively extract fault characteristics and accurately realize classification of bearing under normal, inner race fault, ball fault and outer race fault
Teager-Kaiser energetic trajectory for machine diagnosis purposes
Get PDFIncreased requirements regarding safety, reliability and early detection of failures of industrial machines stimulate the development of new methods and tools for purposes of condition monitoring. The paper presents original concept of the Teager-Kaiser energetic trajectory representing an examined signal on the Teager-Kaiser energy plane. The Teager-Kaiser energetic trajectory illustrates simultaneously changes of instantaneous values of the Teager-Kaiser energy indicator and the velocity of change of the energy indicator. At the beginning of the paper, the Teager-Kaiser energetic trajectory is presented and described followed by examples of trajectories of simulated signals. In the next section, the author presents and discusses the model of signal simulating occurrence of a failure in a gearbox. Finally, the paper presents representations of signals recorded form gearbox during fatigue tests. The paper concludes with the discussion on application options of the Teager-Kaiser energetic plane in condition monitoring of rotation machinery
Modified Hertz-damp model for base-isolated structural pounding simulation under near-fault earthquakes
Get PDFPounding phenomenon between base-isolated structures under near-fault earthquakes has been widely investigated with various impact models around the world. Firstly, the existing impact analysis models are summarized and discussed in this paper. For the Hertz-damp impact model, the damping constant does not coincide with its physical fact. Then, the damping constant in the Hertz-damp impact analysis model was modified based on the Hertz theory. Next, the approximate formula of the damping constant is theoretically derived, and the effectiveness is verified by a simulation analysis. The numerical results show that the pounding can significantly increase the floor acceleration, especially at the isolation layer. In addition, the impact stiffness has a significant effect on the acceleration response, and the inter-story drifts are also sensitive to the variety of impact stiffness. The simulation results indicate that excessive flexibility at the base-isolated system may lead to a susceptible pounding with a limited seismic gap
Numerical simulation and experimental research of metal dynamic flow in cold extrusion under the electric-hydraulic vibration
Get PDFWith thick-wall cylinders as the researched object, the paper adopts a novel cold-extrusion technology, namely electro-hydraulic cold-extrusion, to apply vibration signals into a traditional cold extrusion technology. With volume effects of vibration processing as the theoretical basis, Deform-3D software was used to conduct numerical simulation of metal materials under a traditional extrusion type and an extrusion mode with vibration respectively. Evolution processes of metal flow lines and metal grid flow under two kinds of extrusion types were analyzed and compared in details. Through experimental research, computational results of numerical simulation were verified. Metal flow lines at corners of molded parts were observed and analyzed in particular. Researched results show that the metal flow velocity increased and the bending level of cross-section flow lines of the metal decreased after applying vibration signals compared with the traditional extrusion type. The research indicated that vibration promoted metal flow, reduced resistance of the metal flow, and obtained more uniform deformation of metal materials during plastic molding. Research achievements obtained in this paper provide important theoretical and practical engineering values for effectively applying vibration in mechanical processing fields
Discrete optimal actuator-fault-tolerant control for vehicle active suspension
Get PDFThis paper studies the discrete actuator-fault-tolerant control problem for a vehicle active suspension system under persistent road disturbances. The discrete model of vehicle active suspension with actuator faults is formulated firstly, in which the actuator faults are described as the output of an exogenous system with unknown initial values. By designed a fault diagnoser, the optimal actuator-fault-tolerant controller is derived from the discrete Riccati equation and Stein equations, respectively. Simulation results illustrate that the ride comfort, road holding ability, and suspension deflection can be reduced significantly and the reliability of the vehicle active suspension can be improved
Stability of twin circular tunnels in cohesive-frictional soil using the node-based smoothed finite element method (NS-FEM)
Get PDFThis paper presents an upper bound limit analysis procedure using the node-based smoothed finite element method (NS-FEM) and second order cone programming (SOCP) to evaluate the stability of twin circular tunnels in cohesive-frictional soils subjected to surcharge loading. At first stage, kinematically admissible displacement fields of the tunnel problems are approximated by NS-FEM using triangular elements (NS-FEM-T3). Next, commercial software Mosek is employed to deal with the optimization problems, which are formulated as second order cone. Collapse loads as well as failure mechanisms of plane strain tunnels are obtained directly by solving the optimization problems. For twin circular tunnels, the distance between centers of two parallel tunnels is the major parameter used to determine the stability. In this study, the effects of mechanical soil properties and the ratio of tunnel diameter and the depth to the tunnel stability are investigated. Numerical results are verified with those available to demonstrate the accuracy of the proposed method