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Seismic demand for eccentric wall structures subjected to velocity pulse-like ground motions
Get PDFThe elastic and inelastic seismic demand of shear wall structures, with stiffness, strength and combined-stiffness-and-strength eccentricity, subjected to velocity pulse-like ground motions are investigated. Based on the axial load-bending moment interaction model and eight pulse-like ground motions, nonlinear dynamic time history analyses are conducted to single-story RC eccentric wall structures. The seismic demand is discussed in terms of the displacement, floor rotation and ductility, and the influence mechanism of different eccentricity types is revealed. The results show that the eccentric systems for pulse-like cases experience much higher elastic and inelastic seismic demand comparing to those for non-pulse-like cases. The axial compression ratio has certain effect on the inelastic seismic demand. The stiffness eccentricity is the key factor to the elastic seismic demand, while the strength eccentricity influences the inelastic seismic demand most. It is suggested that the strength eccentricity be added as a parameter in the inelastic analysis of eccentric structures, and the influence of axial load as well as velocity pulse-like effect of ground motions also be accounted in
An analysis of shock isolation characteristics of a head of a woodpecker and its application to a bionic helmet
Get PDFThe effect of a woodpecker’s head structure on shock isolation was investigated from a dynamic point of view. A simplified multi-degree-of-freedom model was set up to study shock isolation characteristics of a woodpecker’s head. The shock-isolation performance of this model was calculated and analyzed by changing the dynamic parameters. And it was evaluated by two indexes: the absolute acceleration of the skull bone and the relative displacement between the skull bone and the beak. A bionic helmet model subjoining the elastic damping layer and the cushion pad was presented. Calculating the three-dimensional shock response surfaces validated it
Experimental study of the effect of drilling pipe on vortex-induced vibration of drilling risers
Get PDFA vortex-induced vibration experiment considers drilling conditions has not been conducted. A new experimental facility was designed to investigate effect of drilling pipe on vortex-induced vibration. Results show that vortex-induced vibration can be inhibited with the increasing drilling pipe tension. Strain amplitude decrease with the increase in drilling pipe tension and strain amplitude decreases significantly with increasing pipe tension at high current speed. Drilling pipe tension does not affect the dominant vibration frequency. Interaction between the IL and CF vibration and the multi-modal phenomenon are more apparent for the periodically contacting and colliding between the drilling pipe and risers
Autoregressive modeling approach of vibration data for bearing fault diagnosis in electric motors
Get PDFThis study investigates the performance of autoregressive (AR) modeling method to detect bearing fault in induction motor. For this purpose, AR models of vibration signals which are acquired during the load performance tests of healthy and seven gradually aged cases of induction motor are constructed. The variation of AR coefficients with model order is compared for all cases of the motor from healthy to faulty. It is seen that sixtieth order model is adequate to reflect the progress of fault characteristics and the first AR coefficient gets bigger with aging. AR modeling error or residuals computed as the difference between original signals and their AR representation gets large in time domain which corresponds to decrease in modeling performance with aging. In addition the error computed as the absolute difference between spectra of the original signals and their AR models gets large in frequency domain and preserves bearing fault features as the energy increase in high frequencies above 1.5 kHz
Identifications of symmetric ductile braced structure by pseudo-single-degree-of-freedom procedure
Get PDFFor energy-dissipation devices, identification of the physical behavior is a more difficult task than their design. This study develops an identification technique that is useful for the acquirement of the dynamic characteristics of buildings with symmetric ductile braces (SDBs) which exhibit bilinear behavior. The considered system is a linear multi-story building with SDBs regarded as a bilinear hysteretic model. The complex multi-degree-of-freedom problem was solved in the pseudo-single-degree-of-freedom domain, and the dynamic parameters of primary building as well as the SDBs are sequentially identified from top to bottom stories based on the input and output responses of floors. To simplify the nonlinear problem, a backbone curve, where the multi-values restoring force is transformed into a single-valued function, is applied to characterize the hysteretic model. A numerical study demonstrates that the proposed identification technique was able to extract the physical parameters of the primary building and the SDBs individually from the floor responses. It may be applied to the health monitoring of buildings protected by nonlinear energy-dissipation devices
Nonlinear resonances of electrostatically actuated nano-beam
Get PDFNonlinear response of electrostatically actuated nano-beam near-half natural frequency is studied by considering the nonlinearities of the large deformation, electrostatic force and Casimir effect. A first-order fringe correction of the electrostatic force, large deformation, viscous damping, and Casimir effect are included in the dynamic model. The dynamics of the resonator are investigated by using the method of multiple scales in a direct approach to the problem. The sufficient conditions of guaranteeing the system stability and a saddle-node bifurcation are studied. The influences of large deformation, damping, actuation, and fringe effect on the resonator response are studied. The peak amplitude of the primary resonance is given in the paper. Numerical simulations are conducted for uniform nano-beam
Nonlinear dynamics modeling and analysis of disc brake squeal considering acting process of brake force
Get PDFDisc brake squeal of automobile is one of the hottest and most difficult issues concerned by automobile manufacturers and researchers. Considering the acting process of brake force, a simplified nonlinear dynamics model is developed in this paper. The nonlinear dynamics equations are set up and solved by theoretical method and numerical calculation. By studying the effects of key parameters on the system’s behavior, the mechanism of brake squeal are analyzed and discussed. The results indicate that the state of system is more sensitive to the fluctuation of brake force than the variation of the negative slope of friction coefficient against the relative velocity between pad and disc. The dynamic characteristics of brake system are greatly connected with the components stiffness. The brake system may become weakly stable and easily produce brake squeal when tangential contact stiffness, normal contact stiffness and connection stiffness satisfy a certain relationship
Modal analysis of cable-tower system of twin-span suspension bridge
Get PDFA three-dimensional finite element model is developed in order to analyze the free vibration characteristics of the tower-cable system of a triple-tower twin-span suspension bridge during the construction phase and right after the erection of the main cable. The dynamic characteristics of each component in the tower-cable system, the isolated side span, main span cables and free-standing towers, are first analyzed separately. The natural frequencies and the vibration modes of the isolated side span and the main span cables obtained from the finite element analysis closely matched the analytical solution from the linear free vibration analysis and verified the validity of the finite element model. The local natural frequency and global natural frequency were defined to categorize the characteristics of the free vibration. The calculation results show that not only does the tower-cable system maintains the information on the modal characteristics of each component in the system, but it also contains its own unique modal characteristics and other important information about the dynamics characteristics of the system. At lower natural frequency range, the swinging motion and in-plane motion are uncoupled. The coupled modal information of the towers and the cables are separated into two groups based on the natural frequencies of the vibration of the main component of the tower-cable system. Some additional natural frequencies and vibration modes are obtained from the finite element analysis depicting the dynamic interaction between the towers and the cables. Furthermore, it is observed that the lower order modes of side span cables couple with the higher order modes of the main span cables. Either in phase or out of phase, local or global modes, the tower-cable system exhibits many new coupled mode combinations that reveal useful information
Vertical vibration reduction and audible sound analysis in surface grinding with electroplated tools
Get PDFOne of the first approaches to the development of a grinding process monitoring system based on audible sound sensors is presented in the paper. Electroplated diamond tools (abrasive D64 and D107) were used in a modified single-disc lapping machine configuration for flat grinding of ceramics (Al2O3). The main aim of the machine modification was to reduce the vertical vibration in order to decrease the tool wear and to increase the material removal rate. The sound generated by the material processing was analysed in the aspect of actual abrasive ability of the grinding tools. The abrasive properties of the tool are decreasing during machining due to the wear of diamond grains. The results from experiments, such as the material removal rates and waveforms of recorded sound are presented and discussed in the paper
Research on fault law of rolling bearing under different fault levels and loads with HHT method
Get PDFBearing is one of the most important components of rotating machinery. The vibration signals are generally nonlinear and nonstationary while operating. The failed rolling bearing will damage to the machine, or cause a serious loss of property. There are a lot of methods about fault diagnosis of bearing, such as shock pulse method, resonance demodulation. Especially the HHT (Hilbert-Huang Transform) method with the adaptive advantage has gradually become a very promising method to extract the characteristics of nonlinear, nonstationary signal. In this paper the variant energy method was introduced in HHT to reduce the computation of the decomposed signal, which effectively improved the computation, and then an experimental platform was designed and established. The bearing fault categories can be diagnosed correctly in dealing with the vibration signals using this method and the fault law is discovered that the trend of the vibration signal fault characteristic frequency amplitude changes with the load increasing. The bearing failure mechanism provides beneficial reference for further research of nonlinear signal analysis