Abstract: A discretization elastic-plastic material model was used for simulating the shock waves transmission within metallic foams. The density heterogeneity of metallic foams was considered. Several types of aluminum foams are studied on the transmission of displacement and stresses wave under impact loading. The results reveal the characteristics of compressive wave propagation within the metal foams. Under low impact pulses, considerable energy is dissipated during the progressive collapse of foam cells, and then reduces the crush of the objects. When the pulse is high sufficiently, on the fixed end of foam, stress enhancement may take place, where high peak stresses usually occur. The magnitude of the peak stress depends on the relative density of foams, the pulse loading intensity, the pulse loading duration as well as the density homogeneity of foam materials. This research offers valuable insight into the reliability of the metal foams used as vehicles and protective structure.
Abstract: The dynamic responses of two kinds of simple-supported beams with single layer and double-layer under a moving load were analyzed based on the theory of nonlinear dynamics. The equations of motion are derived by using Hamilton’s principle and von Karman type equations for the two models. Galerkin’s method was employed to obtain the ordinary differential equations of motion. First we obtain the periodic motion waveforms in the mid-point of the beams at the same initial velocity, and the result show that the amplitude of the double-layer model is much smaller then that of the single-layer model. Then for the two models, the vibration response and critical velocity were studied considering the effect of the structural parameters, the magnitude and velocity of moving load. The results of numerical simulation show that double-layer beam model has better vibration suppression performance than single-layer beam model.
Abstract: Dynamic testing of an inflatable beam has been performed to evaluate structural natural frequencies and modal damping ratios. The inflatable beam has a pattern of six composite fiber strips inside thin-film structure that increases its local stiffness that the structure can be self-supporting in the gravity environment when the internal pressure is released. A measurement setup was installed, and the dynamic testing was performed in this self-supporting state. Dynamic characters of the beams were tested with internal pressure or not when the beam had a 2.0kg mass on the top. Moreover, the dynamic characters before rolled up were contrasted to one after. The experimental results indicate that the self-supporting inflatable beams had better bending stiffness, and the curl folding process had an impact on the dynamic characteristics of the inflatable beam. The pressure affection is not obvious on dynamics of the beam.
Abstract: The study on nonlinear displacement discontinuity model has been investigated in the researches of normal incident wave attenuation across rock joints. But the studies were limited only on the effects of joint with single type deformation behavior, without considering the influence of different extent in model nonlinearity. The improved elastic nonlinear normal deformational model can descript the extent of nonlinearity quantitatively. Based on this model, a displacement discontinuity model for normally incident wave propagation across multiple parallel joints was established in an elastic half-space. Using one-dimensional wave equation characteristics method, the time-domain numerical difference scheme of transmitted particle velocity was proposed, making computational programs to obtain semi-numerical solutions, and transmission coefficients. Parameter studies were conducted to get an insight into the effects of number of joints and the extent of nonlinearity, the incident wave maximum amplitude on transmission coefficients and transmission energy rate, waveform distortion and delay time.
Abstract: Numerical analysis methods in time-domain and frequency-domain are commonly considers as two important ways for seismic evaluation of structure responses. FFT plays a unique role in building the equivalent expression between the structural dynamic signals in time domain and frequency domain, such as computing frequency spectrum values at discrete frequency points for time history data. On the basis of radix-4 and radix-2 FFT techniques, an improved district fast Fourier transfer FFT is presented in this paper to improve the transform efficiency, in which radix-4 transform is applied in most iterative steps, besides radix-2 transform used in the last one iterative step. As compared to the traditional radix-2 FFT, the new mixed-radix FFT leads to distinct reducing in computing amount, while the equivalent precision and the same discrete frequency points remain. Also by taking the trigonometric coefficient method as theoretical results, it’s numerically validated through some examples that the new improved FFT transform technique suits the engineering application of the fast numerical transform in the time and frequency domain for structural frequency spectral analysis.
Abstract: Chirp signal is a typical non-stationary signal, and have been widely used in communication, sonar, radar and so on. So, this signal is worth to analysis. In order to show the characteristics, this paper first introduces the definition and formula of each algorithm, then with all kinds of time-frequency analysis method to the signals, and the signal to add two sine signal noise are analyzed, the comparison of the characteristics of the method in the paper, and the signal for the analysis, the selection of an appropriate analysis. Through analysis and comparison, when dealing with the signal, Hilbert-Huang transformation not only has a better gathered characteristic, but also has a better resolution to distinguish the sine signal noise. Finally, use the MATLAB software simulation to obtain the result.
Abstract: In this paper, a time-frequency analytic system is implemented by using mixed programming of Matlab and Delphi languages based on COM (Component Object Model）module technology. Matlab possesses many signal analytic functions and Delphi has a friendly visual programming environment. These two advantages are fully combined in the mixed programming. This system can be easily upgraded to expand new analytic functions with help of COM module technology. Fault diagnosis of a grinding machine is carried out by using this system. A same vibrational signal sampled from the machine is analyzed in turn by three methods in this system that are Fast Fourier Transform(FFT), Wigner-Ville Distribution(WVD) and Choi-Williams Distribution(CWD). Comparing with the three results, it shows that CWD can get best diagnostic information and validity of the estimation on the instantaneous frequency of a signal. Success of the mixed programming is presented meantime.
Abstract: Studies on leakage and friction have received considerable attention in scroll compressor, especially which between the fitting surface of orbiting scroll and fixed scroll, as they affect the scroll compressor performance. According to the scroll compressor working principle and structure, combined with the force model of the orbiting scroll, the overturning moment on the orbiting scroll was analyzed and verified by a specific example, in which the azimuth angle and of the overturning moment action line were calculated and compared. The results show that the overturning moment will have a significant effect not only on the leak and friction loss at the fitting surface of orbiting and fixed scroll, also on the dynamic characteristics of the orbiting scroll due to the linear change of the azimuth angle and the unstable of the azimuth angle . The result is helpful for the study on leakage, friction, and the dynamics and tribology coupling problem research of scroll compressor.
Abstract: The special structure of beams of cantilever screen has the advantages comparing with the traditional screen and special dynamic characteristics, such as the dynamic characteristics of frequency veering. The traditional analysis method of vibrating screen is not applicable to its dynamic analysis because of the special structure. By analysis and decomposition of stiffness matrix of beams of cantilever screen, the frequency veering phenomenon of the beam of cantilever screen was explained from the point of view of modal energy equation and the influence of sub-stiffness matrix of beams of cantilever screen on the frequency veering was analyzed. The analysis results showed that the sub-stiffness matrix of the hollow beam and sub-stiffness matrix of cantilever bars is the main reason for the segmentation of modal natural frequencies and the coupling stiffness between hollow beam and cantilever bars is the main reason for the concentration of modal natural frequencies and the formation of the regular mode shapes for cantilever bars group.
Abstract: Based on the semi-active suspension system with variable stiffness and damping, the full vehicle model was established in Adams/Car software, which included front suspension and rear suspension with variable stiffness and damping, steering system, car body and tires model. The variable universe fuzzy controller of semi-active suspension was designed according to variable universe fuzzy theory, which was compared with the traditional fuzzy controller. The co-simulation model was built by Matlab/Simulink and Adams/Car software. Then the model was simulated and analyzed in the inputs of random road and roof road. The results of the co-simulation show that, compared with the full vehicle model with passive suspension, the full vehicle model with variable stiffness and damping semi-active suspension effectively reduced the vibration of car body and improved the vehicle ride quality, and the variable universe fuzzy controller is better than the traditional fuzzy controller in decreasing vibration.