Applied Mechanics and Materials Vols. 105-107

Abstract: Considering the contacts between solid and fluid are subjected to dynamic lodes, the influence of vibration characteristic of structure which is coupled with solid and fluid are applied to calculation. In this paper, the calculation formula of structure vibration between solid mass and fluid is derived and the finite element method (FEM) is adopted for discrete of pump station structure and fluid, considering the effect of fluid flow to solid structure, the natural frequency of pump station is acquired. The result shows the method is correct and reasonable.

Abstract: In order to study the influence on structural vibration from pre-stress and eccentricity, a experiment is designed. After analyzing the experimental results of 9 groups of modal tests on a post-tensioned unbonded pre-stress concrete beam, the following conclusions can be drawn: The influences on first order vibration frequency which are caused by eccentricity and pre-stress really exist. The rules of influences brought about by eccentricity and pre-stress on first order vibration frequency are complicated. When the eccentricity is close to the centroid, the linear correlation between the pre-stress and the first natural frequency will be good, on the contrary, the nonlinear will be strengthened. The first order vibrational frequency of the tested beam will go up with the increase of pre-stress.

Abstract: Based on the random vibration and system identification theory, the ambient vibration testing of two adjacent transmission towers were carried out, dynamic characteristics of the towers were obtained from ambient vibration data. The result shown that the suspended cables not only have mass effects, but have coupled stiffness effects applied to tower on transverse direction and longitudinal direction. At the same, testing value shows that the two adjacent towers have basically the same dynamic characteristics and damping ratio of the two transmission towers less than 0.01. Owing to the influence of conductors, frequency of the insulators is different to the towers at the two directions. It is disadvantage for wind-induced response of transmission line system under ambient loads.

Abstract: In order to restrain the regenerative chatter and improve the processing efficiency of thin-walled parts, stability analysis for the milling of thin-walled parts should be the critical element in the whole process of analysis for thin-walled parts. This paper mainly introduces the stability analysis for the milling of thin-walled plates. The two-dimensional stability lobes of milling of plate plotted, the effect of different modal parameters on the stability of milling of plate is investigated. It is shown that single mode will reduce the range of stability zone of main mode if the stability lobes of single mode are intersectant with that of main mode and the range of stability zone will be larger and the stability lobes will be regular on condition that the mode is symmetrical.

Abstract: Shock wave focusing by an ellipsoidal reflector can produce higher pressure in the focal region. The focusing process of shock wave was studied by theory analyses and numerical results. Base on the experimental observation the shock wave source is equivalent to the explosion of an underwater explosive. A finite element model was set up to investigate the shock wave focusing behaviors. Both the pressure-time history and the peak pressure along the axial position were presented. The shock wave focusing process was shown. The interactions of waves in the focal region are shown. A modified EOS of water was applied, which can be used to analyze the negative pressure observed; the numerical results based on the modified EOS agree well with the experimental data.

Abstract: Acoustic wave propagation in fluid-saturated porous cylindrical shell is investigated in this paper by using the Biot’s theory. The Expressions for acoustic pressure and radical displacement in and out fluid, the expressions for components of solid and filtration displacement and pore fluid pressure and stress tensor are given. The numerical simulation is operated on acoustic field in fluid of poroelastic cylindrical shell, and the full-waveform is obtained by Fourier transform, and acoustic pressure field in frequency-wavenumber domain is analyzed, as well as the influence of inner and outer radii on wave amplitude is discussed. It shows that if the thickness of shell remains constant, the amplitude of longitudinal mode increases and that of Stoneley wave decreases when inner and outer radii increasing. In the fast formation the influence of inner and outer radii on the amplitude of longitudinal mode is notable. In the slow formation the amplitude of Stoneley wave will decrease with inner and outer radii increasing.

Abstract: The asymptotic Lyapunov stability with probability one of Mathieu-Van der Pol system with time-delayed feedback control under wide-band noise parametric excitation is studied. First, the time-delayed feedback control force is expressed approximately in terms of the system state variables without time delay. Then, the averaged Itô stochastic differential equations for the system are derived by using the stochastic averaging method and the expression for the Lyapunov exponent of the linearized averaged Itô equations is derived. It is inferred that the Lyapunov exponent so obtained is the first approximation of the largest Lyapunov exponent of the original system, and the asymptotic Lyapunov stability with probability one of the original system can be determined approximately by using the Lyapunov exponent. Finally, the effects of time delay in feedback control on the Lyapunov exponent and the stability of the system are analyzed. The theoretical results are well verified through digital simulation.

Abstract: The effects of tripping rods on characteristics and fluid forces acting on a single cylinder was three-dimensional numerical studied in a low laminal flow at a Reynolds number of 200 and a subcritical stream at a Reynolds number of 5.5X104. The angular position of the tripping rods was varied from 20 to 60.The results reveal that there exits an optimum position of tripping rod for reducing fluid forces. This optimum angular position was found to be 40° for Re=200 and 30° for Re=5.5X104. At this optimum angle, the steady drag, fluctuating drag and fluctuating lift forces acting on the cylinder are reduced by 21%, 32%, and 28% for Re=200 and 36%, 44%, 76% for Re=5.5X104.

Abstract: Satellite solar panel bears with crucial responsibility in supplying energy while satellite orbits the moon. Through analyzing the vibration mode of solar panel, the structure’s natural frequency and inherent vibration vector can be obtained, which is of vital importance to structure dynamic modification, structure optimization design and fault diagnosis.This article summarizes the experimental results and analysis of solar panel under vibration with the aid of LDV. Through binary channel fast Fourier Transform (FFT), combined with modal analysis theories and software analysis system, a modal model of solar panel is built. Such an modal model provides a basis for the determination of the physical and structural parameters in the solar panel design of a satellite and provides an analysis method for the reliability validation of the design and the operating reliability of the satellite.

Abstract: The paper studies the dynamical behaviors of a recurrent neural network model consisting of three neurons with time delays through theoretical analysis and numerical simulations. The local stability of the trivial equilibrium of the network is analyzed and the sufficient conditions of the existence of Hopf bifurcation are given by discussing the associated characteristic equation. The direction and stability of the bifurcated periodic oscillations arising from Hopf bifurcation, which depend on the nonlinear terms of the network, are determined by means of the normal form and the center manifold theorem. Afterwards, numerical examples are performed to validate the theoretical analysis. The case studies of numerical simulations reach nice agreement with the theoretical results.