Applied Mechanics and Materials Vols. 117-119

Abstract: Mono-crystalline silicon experiences various phase transformations under different loading conditions. This paper reveals, with the aid of molecular dynamics simulations, that scratching the silicon {001} surface along the [110] direction under a load of 0.8 µN or more would produce stable 5 coordinated body centered tetragonal (bct-5) silicon in the subsurface. By examining the effect of this bct-5 silicon on indentation, it was found that the resistant to deformation of bct-5 silicon is higher than a-Si but lower than diamond Si.

Abstract: Large eddy simulation (LES) was made to solve the flow around two simplified CRH2 high speed trains passing by each other at the same speed in a long tunnel base on the finite volume method and dynamic layering mesh method and three dimensional incompressible Navier-Stokes equations. Wind tunnel experimental method of resting train with relative flowing air and dynamic mesh method of moving train were compared. The results of numerical simulation show that the flow field structure around train is completely different between wind tunnel experiment and factual running. Two opposite moving couple of point source and point sink constitute the whole flow field structure during the high speed trains passing by each other. All of streamlines originate from point source (nose) and finish with the closer point sink (tail). The flow field structure around train is similar with different vehicle speed in a long tunnel, and they have a little difference with on the ground.

Abstract: The Reynolds-Orr energy equation is generalized to include the velocity slip effect at the walls, for investigating the energy gain or loss in the disturbed slip flow. Taken the Poiseuille flow, typical prototype of parallel shear flows as an example, it is found that for the very weak effect of wall slip, the disturbance energy being transferred from the basic flow overcomes the viscous dissipation, resulting in the growth of disturbance energy and the destabilizing role of wall slip. Otherwise, the viscous dissipation overcomes the energy production resulting in the decay of the disturbance energy and the stabilizing role of wall slip.

Abstract: Fumed Silica was modified with hexamethyldisiazane (HMDZ, modifier) and dimethyldiethoxysilane (DMDEOS, co-modifier) by grafting method. The structure of organo-functionnalized nanoparticles was characterized by fourier transform infrared spectrum (FT-IR) and transmission electron microscopy (TEM). Functional nanosilica-filled polydimethylsiloxane(PDMS) composites membrane were prepared. Scanning electron microscopy (SEM) observations of composites revealed good dispersion of the silica nanoparticles and the pervaporation performance of the filled PDMS membranes is better than that of the unfilled PDMS membranes.

Abstract: The vibrational resonance (VR) and stochastic resonance (SR) phenomena in time-delayed FitzHugh-Nagumo (FHN) neural model, driven by one high-frequency (HF) signal and one low-frequency (LF) signal, with coupled multiplicative and colored additive noise, is investigated. For the case that the frequency of the HF signal is much higher than that of the LF signal, under the adiabatic approximation condition, the expression of the signal-to-noise ratio (SNR) with respect to the LF signal is obtained. It is shown that, the SNR is a non-monotonous function of the amplitude and frequency of the HF signal. In addition, the SNR varies non-monotonically with increasing the intensities of the multiplicative and additive noise, with increasing the delayed-time as well as increasing the system parameters of the FHN model. The influence of the correlation time of the colored additive noise and the coupling strength between the multiplicative and additive noise on the SNR is discussed.

Abstract: Based on the investigation of vehicle loads, the model of the random dense vehicle load was simulated, and three different degree dense vehicle loads were obtained with the simulated model. The calculated results show that the random dense vehicle loads moving on the bridge structures is very dangerous for the security of the structures; the combination factor 1.4 designed in the code is not precise for the situation of random dense vehicle loads, and it is suitable for the common vehicle loads.

Abstract: For its construction convenience and structure integrity, cofferdams are widely employed in port engineering. Past experience has shown that cofferdam are subjected to damage due to earthquake excitations. Numerical analyses with both response spectrum and step-by-step integration methods are conducted by using Lanczos eigenvalue extraction technique to obtain natural frequencies and modes, and solving dynamic equations with Newmark implicit method to consider geometric nonlinearity. The computational results show that the natural frequency of cofferdam system is low and the horizontal translation stiffness of cofferdam in positive direction is higher than that in negative direction. Under seismic excitation, the displacement response of inner steel sheet is much more obvious than that of outer one. And the distribution of horizontal displacements in steel sheets presents the characteristics that the corresponding values increase with their heights in the cofferdam system. On the contrary, the deviatonic stresses of cofferdam decrease with the augments of height.

Abstract: This study was designed to compare the biomechanical effects of three posterior fixations for thoracolumbar burst fractures using the finite element (FE) method. Five T11-L1 FE models, including the intact, the fractured at T12, the monosegment fixated at the level of the fracture, the short-segment fixated with four pedicle screws and the short-segment fixated with five pedicle screws, were created. And four loading conditions (flexion, extension, lateral bending and torsion) were imposed on these models and deformations in these models under different loading conditions were calculated by finite element method. The biomechanical effects of the three different pedicle screw fixations for thoracolumbar burst fractures were compared and analyzed. The results showed that the displacement level in monosegment fixation model was close to that in the intact one. The extension motion was more limited in short-segment fixation models than that in monosegment fixation model. Under the lateral bending condition, the level of the displacements in these models were similar and the peak rotation angles in the three fixation models were close to that in the intact one. The displacements in fractured T12 were increased in monosegment fixation model under all loading conditions. These indicated that the monosegment fixation couldn’t provide desirable stability for the fractured T11-L1 and the short-segment fixation with five pedicle screws was the best selection because of ideal stability and movability.

Abstract: stochastic resonance; time-delayed Logistic growth model; signal-to-noise ratio Abstract. The stochastic resonance in a time-delayed Logistic growth model subject to correlated multiplicative and additive white noise as well as to multiplicative periodic signal is investigated. Using small time delay approximation, we get the expression of the signal-to-noise ratio (SNR). It is found that the SNR is a non-monotonic function of the system parameters, of the intensities of the multiplicative and additive noise, as well as of the correlation strength between the two noises. The effects of the delay time in the random force is in opposition to that of the delay time in the deterministic force.

Abstract: A gas-solid flow model of transmission line surrounded by sand storm is built. Numerical simulation under different velocity, different sand diameter and different transmission line diameter situation is taken to obtain the volume fraction distribution of sand around the transmission line. Finite element-image method is chosen to build a sand-electricity coupling model made up of high voltage transmission line and sand around transmission line. Electric field distribution of transmission line with sand around it is obtained. Analysis results show that the model is effective.