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Concrete creep and thermal effects on the dynamic behavior of a concrete-filled steel tube arch bridge
Get PDFA solution to the dynamic problem of concrete-filled steel tube arch bridge including concrete creep and thermal effects are presented. Using a new method to calculate the creep of axially compressed concrete-filled steel tube members, the predicted values of the stress and deformation of the Yajisha Bridge in China are consistent with the site measured data. Using the elastic continuation and plastic flow theory and the unified theory of concrete-filled steel tube columns, the dynamic responses of the Yajisha Bridge are analyzed. The influence of creep effects is more significant, especially in the early aging of concrete. It is found that temperature deteriorates the modulus of elasticity of concrete significantly. Consequently the natural frequencies decrease with temperature increase. Concrete creep and thermal effects are essential to evaluate dynamic behavior of concrete-filled steel tube arch bridge
Application of fuzzy random finite element method on rotor dynamics
Get PDFFuzzy and stochastic characteristics of parameters exist widely in rotating machinery. To research the parameters characteristics is of great significance in rotor dynamics. Dynamic characteristics of rotor system are analyzed taking into account uncertain properties of fuzzy and stochastic coexisting. Fuzzy variables are transformed into stochastic variables based on information entropy theory. The Neumann stochastic finite element method based on Neumann expansion combined with Newmark-β method is used in linear and nonlinear rotor system within the frame work of Monte Carlo simulation. Critical speed and dynamic response of fuzzy stochastic rotor systems are described by the proposed method. The results show that the Neumann stochastic finite element method has good applicability and efficiency in rotor dynamics
Experimental and numerical studies on multi-spherical sliding friction isolation bearing
Get PDFAn innovative multi-spherical sliding friction isolation (MSFI) bearing has recently been developed. The novel isolator has efficient energy dissipation capacity and enough displacement capacity under strong earthquake excitations. The MSFI bearing is completely passive devices, yet shows smart stiffness and smart damping under external excitation. The principles of operation and force-displacement relationship of the novel isolator are presented in this paper. The sliding order of all sliding surfaces and force-displacement hysteretic relationship are verified through a displacement-control testing program, and numerical analysis of the MSFI bearing under low cyclic loading is carried out based on ABAQUS program. The results show the sliding order and force-displacement relationship of the MSFI bearing derived from theoretical analysis results and numerical simulation results are well agree with experimental data which the compression-shear testing of the MSFI bearing specimen with the identical curvature radii and friction coefficients. The adaptive behavior of MSFI bearing permits the isolation system to be separately optimized for multiple levels of seismic intensity and ground motions
Diagnostic analysis of dynamic deflection for cracked asphalt pavements under FWD impulsive loading
Get PDFThe falling weight deflectometer (FWD) is a non-destructive testing technology used to calculate the stiffness-related parameters of pavement structures and has been widely used in the pavement engineering field. Deflection basin testing data have an obviously affecting effect on the modulus backcalculation of an asphalt pavement. Identifying effective data of dynamic deflection basins is an important task to perform modulus backcalculation. The objective of this paper is to study the distribution features of dynamic deflection basins of cracked asphalt pavements using a three dimension dynamic finite element method. Based on the systematic analysis, the criteria used to filter effective data of FWD deflection basins were presented and verified with an in-situ case study. The study results demonstrated that the crack width of 0.2 mm was a critical value to determine the existence of contact behavior between vertical crack surfaces. The distribution characteristics of dynamic deflection basins showed a significant difference between intact and cracked pavements. The established criteria, involving surface deflection indicator and surface modulus indicator, were verified to be reasonable and viable for filtering the FWD testing data
Dynamics analysis of electric shoegear and conductor rail system
Get PDFAccording to characteristics of electric shoegears and conductor rail, ashoegear can be simplified as a cantilever with rotating mechanism, while the rail can be reduced to a simply supported Euler-Bernoulli beam. Assuming that there is no separation between them, a unified dynamics formation of electric shoegear and conductor rail system has been formed, which is second order partial differential equations with multiple degrees of freedom. Substituting modal displacement of electric shoegear and conductor rail into Lagrange dynamic equations, modal coordinates would be obtained. Given actual parameters of the system, the results show that the shoegear and the rail arevibrated more intensely with the speed increasing. Based on movement principle of electric shoegear, its FEM model can be built according to parameters measured in vibration test. Meanwhile it is not difficult to obtain the FEM model of conductor rail. Then vibration of the system according to practical parameters can be solved by numerical integration method. Throughthe analysis of contact force and vibration acceleration of sliding plate and conductor rail, it is realized that when speed is over 120 km/h, the contact condition gets worse sharply which indicates that the recommended speed for electric shoegear and conductor rail system is 120 km/h in the case of the practical operating parameters
Earthquake response and effect of adjacent structures founded at different depths
Get PDFThis paper deals with the earthquake response and effect of adjacent structures founded at different depths. In this paper, the dynamic time history analyses were performed using structural analysis program developed in this research, both the structure and the soil were represented by plane stress or plane strain elements, with response quantities to be interpreted from the stresses obtained at element centers. The elasticity modulus of the ground is varied. Just like the modification of elasticity modulus, the varying relations of inertia have a strong influence on the section forces within the structures. Two structures with different foundation depths and the same foundation levels were represented by the three different systems. The interaction of the proposed method and programs was demonstrated and discussed with numerical examples. As a result, the greatest difference between two structures could be observed in the shallow and deep foundations. Concerning the plane stress model, the calculation of section forces reveals that the greatest difference was also in the shallow and deep foundations. If case of both structures having shallow foundations, the interaction was small and negligible. If one structure is shallow and the other one deep, then the interaction renders the forces in one structure 20 % smaller than those in a single shallow structure, If the adjacent structures have the same deep foundation level, then due to interaction the forces in one structure are 25 % larger than those in a single deep structure
An approach to performance assessment and fault diagnosis for hydraulic pumps
Get PDFThe hydraulic pump is the heart of the hydraulic system. Therefore, monitoring the condition of such a pump in real time is crucial to the reliability of the entire system. In this study, a method that assesses the performance of and diagnoses faults in hydraulic pumps is proposed. This method is based on wavelet packet transform (WPT) and a self-organizing mapping (SOM) neural network. First, WPT is used to decomposes the vibration signal into components. The energy of each component is then extracted and normalized to form feature vectors. Second, the SOM neural network, which is trained by normal data only, maps feature vectors into minimum quantization errors, which are then normalized into confidence values (CVs). Performance is assessed by tracking CV trends. Finally, SOM, which is trained by both normal and faulty samples, classifies faults into different groups when they occur. These groups represent the various fault modes of the hydraulic pump. In addition, Taguchi method is employed to reduce the number of redundant features and extract the principal components, thereby ensuring the effectiveness of the approach. A case study based on the vibration dataset of the rig of a test plunger pump is conducted to demonstrate the ability of the proposed method to assess the performance of a hydraulic pump and suitably diagnose faults
Nonlinear vibration modeling and bifurcation characteristic study of a planetary gear train processing device
Get PDFIn this paper, a nonlinear torsional vibration model with meshing errors, time varying meshing stiffness, damping coefficients and gear backlashes was established and dimensionless equations of the system are derived in the planetary gear train processing device. The paper analyzed the nonlinear dynamic behavior of the device which was used to machine the Circular-Arc-Tooth-Trace cylindrical gear. By using the method of numerical integration, the bifurcation diagrams are obtained and the results indicate that the processing device has abundant bifurcation characteristics with the change of the dimensionless speed, and the damping ratios, gear backlashes and meshing errors of meshing pairs could influence the vibration greatly. The bifurcation diagrams reveal that increasing the damping ratios can change the bifurcation and the chaos can be avoid when the damping ratios are bigger enough, reducing the gear backlashes can reduce the dimensionless displacement amplitudes, increasing the meshing errors can make the bifurcation diagrams shift left for a distance, and alternating load torque with large amplitude will cause complex chaos phenomenon. The study can help to avoid the fatigue failure and instabilities caused by chaos and it also contribute to improving the performance of the processing device
A new method for spectral analysis of non-stationary signals from impact tests
Get PDFTo obtain the spectrum of impulse response from impact test, the paper proposes an approach based on envelope of cross-correlation function. This is achieved by correlating the impulse response and reference single-harmonic signals. An envelope of cross-correlation makes it possible to detect and identify the harmonics of impulse response. The presented method gives a possibility to point the frequency value of the harmonic component of an impulse response signal independently of the commonly used fast Fourier transform. Its main advantage over the fast Fourier transform is that the spectral resolution does not depend on duration of the impulse response
Dynamic research of angle measurement comparator
Get PDFThe main aim of the research is to determine (by experiment) the dynamic characteristics of angle comparator carriage on which optical system is attached on it and to compare the experiment with the results obtained by theoretical calculations