用高阶单元分析平面应力结构的自由振动

基于YKCheung带面内转角的平面应力单元 ,提出了一种用于剪力墙结构自由振动分析的 32～ 5 6自由度的高阶单元 ,单元的每个节点采用u ,u/x和v ,v/x为自由度 ,在墙体水平方向采用 3次Hermite函数 ,铅垂方向采用了 3～ 6次Lagrange多项式 ,对开孔墙体则提出了按剪切刚度等效和质量密度等效的连续化方法 .为了克服高阶元列式复杂的困难 ,采用下标求和形式的表达式通过标准有限元过程获得了单元刚度矩阵和质量矩阵 ,再用迭代法计算结构自振频率 给出了 5个算例 ,验证了高阶元所具有的高精度 ,并发现了剪力墙结构前3阶振型中当高宽比H/B≤ 10时 ,第 3阶振型为竖向振动 ,而当H/B≤ 2时 ,第 2 。

Prediction of blast-induced ground vibrations via genetic programming

Excessive ground vibrations, due to blasting, can cause severe damages to the nearby area. Hence, the blast-induced ground vibration prediction is an essential tool for both evaluating and controlling the adverse consequences of blasting. Since there are several effective variables on ground vibrations that have highly nonlinear interactions, no comprehensive model of the blast-induced vibrations are available. In this study, the genetic expression programming technique was employed for prediction of the frequency of the adjacent ground vibrations. Nine input variables were used for prediction of the vibration frequencies at different distances from the blasting face. A high coefficient of determination with low mean absolute percentage error(MAPE) was achieved that demonstrated the suitability of the algorithm in this case. The proposed model outperformed an artificial neural network model that was proposed by other authors for the same dataset.

Photodetachment of H^- Near a Dielectric Surface

Using the closed orbit theory, the photodetachment cross section of H- near a dielectric surface has been derived and calculated. The results show that the dielectric surface has great influence on the photodetachment process of negative ion near the ionization threshold. Above the ionization threshold, the photodetachment cross section starts to oscillate. With the increase of the energy, the oscillating amplitude decreases and the oscillating frequency increases. The oscillation in the photodetachment cross section of H- in the presence of a dielectric surface is either larger or smaller than the photodetachment of H- without the surface. As the photon energy is larger than the critical value Epc, the oscillatory structure disappeared and the cross section approaches to the case of the photodetachment of H- without any external fields. For a given detached-electron energy, the photodetachment cross section becomes decreased with the increase of the ion-surface distance. Besides, the dielectric constant has great influence on the photodetachment of H-. With the increase of the dielectric constant, the oscillation in the cross section becomes increased. As the dielectric constant increases to infinity, the cross section is the same as the photodetachment of H- near a metal surface. This study provides a new understanding on the photodetachment process of H- in the presence of a dielectric surface.

Effects of surface finish and treatment on the fatigue behaviour of vibrating cylinder block using frequency response approach

This paper presents the effects of surface finish and treatment on the high cycle fatigue behaviour of vibrating cylinder block of a new two-stroke free piston engine at complex variable amplitude loading conditions using frequency response approach. Finite element modelling and frequency response analysis was conducted using finite element analysis software Package MSC.PATRAN/MSC.NASTRAN and fatigue life prediction was carded out using MSC.FATIGUE software. Based on the finite element results, different frequency response approach was applied to predict the cylinder block fatigue life. Results for different load histories and material combinations are also discussed. Results indicated great effects for all surface finish and treatment. It is concluded that polished and cast surface finish conditions give the highest and lowest cylinder block lives, respectively; and that Nitrided treatment leads to longest cylinder block life. The results were used to draw contour plots of fatigue life and damage in the worst or most damaging case.

Oscillations in Total Photodetachment Cross Sections of a Triatomic Anion

The total photodetachment cross section of a linear triatomic anion is derived for arbitrary laser polarization direction. The cross section is ,shown to be strongly oscillatory when the laser polarization direction is parallel to the axis of the system; the oscillation amplitude decreases and vanishes as the angle between the laser polarization and the anion axis increases and becomes perpendicular to the axis. The average cross section over the orientations of the triatomie system is also obtained. The cross section of the triatomic anion is compared with the cross section of a two-center system. We find there are two oscillation frequencies in the triatomie anion in contrast to only one oscillation frequency in the two-center case. Closed-orbit theory is used to explain the oscillations.

Methanol Adsorption on TiO2 Film Studied by Sum Frequency Generation Vibrational Spectroscopy

A broadband infrared surface sum frequency generation vibrational spectroscopy （SFG-VS） and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO2 thin film surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa 02 atmosphere. We obtained the methanol spectrum in the CH3 stretching vibration region on TiO2 surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH3 symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6-8 cm-1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on Surfaces in vacuum was also observed. Our results suggest two equilibria exist： between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.

Influence of Oscillation Frequency of a Sieve on the Screening Process for a Conical Sieve with Oscillatory Circular Motion

Removal of foreign bodies from seed mixtures, or their calibration for use as planting material, as well as fraction classification of granular materials requires screening surfaces with vibratory motion. This paper presents some aspects on the working process of a sieve, made of perforated sheet and having an outer conical surface with oscillatory circular motion （alternative） on the horizontal. Results are presented for some experimental researches on the movement of material on the sieve, for various kinematical parameters of the sieve （amplitude and oscillation frequency）. A conical sieve, suspended at the upper and lower in three points, was tested for screening of rapeseeds in order to estimate the influence of oscillation frequency on the screening process. Curves were drawn for separation intensity on the sieve generating line, and by regression analysis with normal distribution law were determined the equation coefficients and the correlation with experimental data. Movement of material on the sieve and its working process, in general, was appreciated by means of the peak position of distribution curve depending on the oscillation frequency of the sieve, considering that the normal distribution law correlates very well the data obtained by experiments.

Natural frequency of tapered high pier considering pile-soil interaction

In seismic design of tapered high pier, the analysis of natural vibration frequency is of great importance. According to the engineering features of tapered high pier in mountainous area, a vibration calculation model was set up considering the tapered pier characteristics and pile-soil interaction. Based on Southwell frequency composition theory, it consists of elastic deformation of bridge pier and the rigid deformation of group piles, which are respectively solved by the finite-element method and energy method, and then the natural frequency is derived. The comparison between the measured and calculated results shows that the calculation errors with and without considering pile-soil interaction are 4.9% and 14.7%, respectively. Additionally, the main parameters (pier height, section variation coefficient and lateral foundation horizontal proportional coefficient) affecting natural frequency were investigated. The result shows that natural frequency ascends with the increase of the lateral foundation horizontal proportional coefficient; and it is quite necessary to consider the pile-soil interaction in natural frequency calculation of tapered high pier.

The Surface Plasmons＇ Frequencies of Two Adjacent Metallic Nanospheres by Bloch-Jensen Hydrodynamical Model

The wave guides and optical fibers have long been known to transmit light and electromagnetic fields in large dimensions. Recently, surface plasmons, which are collective plasma oscillations of valence electrons at metal surfaces, have been introduced as an entity that is able to guide light on the surfaces of the metal and to concentrate light in subwavelength volumes. It has been found that periodic array of metallic nanospheres, could be able to enhance the light transmission, and guiding light at nanoscale. The coupling between two nanoparticles in these devices is very important. The Bloch-Jensen hydrodynamical method has been used for computing surface plasmons＇ frequencies of a single metallic nanosphere. It contains the entire pole spectrum automatically, so it is more exactly than the other computational methods. In this research, we have computed the surface plasmons＇ frequencies of two adjacent nanospheres by Bloch-Jensen hydrodynamical model for the first time. The results show that there are two modes for this system, which depend explicitly on interparticle spacing. In addition, we have shown that the excitation modes yield to a single mode of a nanoparticle as the interparticle spacing increases.

Area spectra of BTZ black holes via periodicity

Motivated by the recent work that the periodicity of a black hole is responsible for the area spectrum,we exclusively utilize the period of motion of an outgoing wave,which is shown to be related to the vibrational frequency of the perturbed black hole,to study area spectra of a non-rotating BTZ black hole and a rotating BTZ black hole.It is found that the area spectra and entropy spectra for both space times are equally spaced.In addition,we find that though the entropy spectra of the 3-dimensional BTZ black holes take the same form as those of the 4-dimensional black holes,the area spectra depend on the dimension of space times.Our result confirms that the entropy spectrum of a black hole is more fundamental than the area spectrum.