AUTOROTATION OF TWO TANDEM TRIANGULAR CYLINDERS

The autorotation of two tandem triangular cylinders at different gap distances is investigated by numerical simulations. At the Reynolds number of 200， three distinct regimes are observed with the increase of gap distance: namely, angular oscillation, quasi-periodic autorotation and ‘chaotic’ autorotation. For various gap distances, the characteristic of vortex shedding and vortex interaction are discussed. The phase graphs (angular acceleration vs. angular velocity) and the power spectra of moment are analyzed to characterize the motion of the cylinder. The Lyapunov exponent is also calculated to identify the existence of chaos.

Chaotic dynamic analysis of viscoelastic plates

The dynamic buckling of viscoelastic plates with large deflection is investigated in this paper by using chaotic and fractal theory. The material behavior is given in terms of the Boltzmann superposition principle. in order to obtain accurate computation results, the nonlinear integro-differential dynamic equation is changed into an autonomic four-dimensional dynamical system. The numerical time integrations of equations are performed by using the fourth-order Runge-Kutta method. And the Lyapunov exponent spectrum, the fractal dimension of strange attractors and the time evolution of deflection are obtained. The influence of geometry nonlinearity and viscoelastic parameter on the dynamic buckling of viscoelastic plates is discussed.

Characteristic Dimensionless Numbers in Multi-Scale and Rate-Dependent Processes

For this sake, the macroscopic equations of mechanics and the kinetic equations of the microstructural transformations should form a unified set that be solved simultaneously. As a case study of coupling length and time scales, the trans-scale formulation

Effects of the Spanwise Characteristic Length on the Transition Feature in the Wake of a Cylinder

The transition features of the wake behind a uniform circular cylinder at Re = 200, which is just beyond the critical Reynolds number of 3-D transition, are investigated in detail by direct numerical simulations of 3-D incompressible Navier-Stokes equations. The spanwise characteris-tic length determines the transition features and global properties of the wake.

A Study on the Microstructure Characteristic of the Cold-Rolled Deformed Nanocrystalline Nickel

In this paper the microstructure characteristic of the cold-rolled deformed nanocrystalline Nickel metal has been studied by transmission electron microscopy (TEM). The results show that there were step structures near by grain boundary (GB), and the contrast of stress field in front of the step corresponds to the step in the shape. It indicates that the interaction between twins and dislocations is not a necessary condition to realizing the deformation. In the later stage of the deformation when the grain size became about 100 nm, the deformation occurs only depend upon the moving of the boundary of the stack faults (SFs) which result from the imperfection dislocations emitted from GBs. In the other word, the movement of the boundary dislocations of SFs results to growing-up of the size of the SFs, therefore realizes deformation. However, when the size of stack faults grows up, the local internal stress which is in front of the step gradually becomes higher. When this stress reach a critical value stopping the gliding of the partial dislocations, the SFs will stop growing up and leave a step structure behind.

Using wavelet transform to study the Lipschitz local singular exponent in wall turbulence

In this paper, wavelet,transform is introduced to study the Lipschitz local singular exponent for characterising the local singularity behavior of fluctuating velocity in wall turbulence. I, is found that the local singular exponent is negative when the ejections and sweeps of coherent structures occur in a turbulent boundary layer.

Long-range automaton models of earthquakes: Power-law accelerations, correlation evolution, and mode-switching

We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r(-p) dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology.

Effects of adiabatic exponent on Richtmyer-Meshkov instability

We present a systematical numerical study of the effects of adiabatic exponent gamma on Richtmyer-Meshkov instability (RMI) driven by cylindrical shock waves, based on the gamma model for the multi-component problems and numerical simulation with high-order and high-resolution method for compressible Euler equations. The results show that the RMI of different gamma across the interface exhibits different evolution features with the case of single gamma. Moreover, the large gamma can hold back the development of nonlinear structures, such as spikes and bubbles.

Direct dynamical test for deterministic chaos and optimal embedding of a chaotic time-series

We propose here a local exponential divergence plot which is capable of providing an alternative means of characterizing a complex time series. The suggested plot defines a time-dependent exponent and a ''plus'' exponent. Based on their changes with the embedding dimension and delay time, a criterion for estimating simultaneously the minimal acceptable embedding dimension, the proper delay time, and the largest Lyapunov exponent has been obtained. When redefining the time-dependent exponent LAMBDA(k) curves on a series of shells, we have found that whether a linear envelope to the LAMBDA(k) curves exists can serve as a direct dynamical method of distinguishing chaos from noise.

Direct dynamical test for deterministic chaos

We present a direct and dynamical method to distinguish low-dimensional deterministic chaos from noise. We define a series of time-dependent curves which are closely related to the largest Lyapunov exponent. For a chaotic time series, there exists an envelope to the time-dependent curves, while for a white noise or a noise with the same power spectrum as that of a chaotic time series, the envelope cannot be defined. When a noise is added to a chaotic time series, the envelope is eventually destroyed with the increasing of the amplitude of the noise.

Local exponential divergence plot and optimal embedding of a chaotic time-series

we propose here a local exponential divergence plot which is capable of providing a new means of characterizing chaotic time series. The suggested plot defines a time dependent exponent LAMBDA and a ''plus'' exponent LAMBDA+ which serves as a criterion for estimating simultaneously the minimal acceptable embedding dimension, the proper delay time and the largest Lyapunov exponent.

Temporal characteristic simulation for stimulated emission depletion microscopy

The imaging technology of stimulated emission depletion (STED) utilizes the nonlinearity relationship between the fluorescence saturation and the excited state stimulated depletion. It implements three-dimensional (3D) imaging and breaks the diffraction barrier of far-field light microscopy by restricting fluorescent molecules at a sub-diffraction spot. In order to improve the resolution which attained by this technology, the computer simulation on temporal behavior of population probabilities of the sample was made in this paper, and the optimized parameters such as intensity, duration and delay time of the STED pulse were given.

Absorption characteristic and nonvolatile holographic recording in LiNbO3 : Cr : Cu crystals

The absorption characteristic of lithium niobate crystals doped with chromium and copper (Cr and Cu) is investigated. We find that there are two apparent absorption bands for LiNbO3:Cr:Cu crystal doped with 0.14 wt.% Cr2O3 and 0.011 wt.% CuO; one is around 480 nm, and the other is around 660 nm. With a decrease in the doping composition of Cr and an increase in the doping composition of Cu, no apparent absorption band in the shorter wavelength range exists. The higher the doping level of Cr, the larger the absorbance around 660 nm. Although a 633 nm red light is located in the absorption band around 660 nm, the absorption at 633 nm does not help the photorefractive process; i.e., unlike other doubly doped crystals, for example, LiNbO3:Fe:Mn crystal, a nonvolatile holographic recording can be realized by a 633 nm red light as the recording light and a 390 nm UV light as the sensitizing light. For LiNbO3:Cr:Cu crystals, by changing the recording light from a 633 nm red light to a 514 nm green light, sensitizing with a 390 nm UV light and a 488 nm blue light, respectively, a nonvolatile holographic recording can be realized. Doping the appropriate Cr (for example, N-Cr = 2.795 X 10(25)m(-3) and N-Cr/N-Cu = 1) benefits the improvement of holographic recording properties. (c) 2005 Optical Society of America.