柔性被动隔振系统的功率流传递特性研究

对柔性被动隔振系统的功率流传递特性进行研究,建立了隔振器倾斜放置的隔振系统的理论模型,运用机械导纳法推导了系统的功率流传递函数．数值仿真中,分别考虑了无限板和有限板、厚板和薄板的情况,通过大量的数值仿真对这些情况的功率流特性进行了详细研究,得到一些对工程实际具有借鉴意义的结论．     

Unsaturated soil slope characterization with Karhunen–Loève and polynomial chaos via Bayesian approach

Engineering with Computers - Field measured data reflect real response of soil slopes under rainfall infiltration and can provide representative estimates of in situ soil properties. In this study,...     

The Shrinkage Characteristic of a Spherical Cavity in Three-Dimensional Piezoelectric Grain

In this article, an analytical method is presented to solve the shrinkage rate and the healing history of a spherical cavity in three-dimensional piezoelectric grains under electric field, interface pressure, and internal gas pressure. From example calculations, it is seen that because of the influence of piezoelectric characteristics and electric fields, a spherical cavity in three-dimensional piezoelectric grain subjected to hydrostatic interface pressures does not completely eliminate, which is obviously consistent with some experimental observations from the micro-hole healing process. The result is useful to reveal the healing mechanism of defects in piezoelectric materials under electric and mechanical loads.     

Tunnel waterproofing practices in China

Water ingress in transportation tunnels not only will shorten the durability of concrete lining and reduce the function of establishments in the tunnel, but also will worsen the tunnel surrounding so much that the traffic will be greatly affected. In this situation, therefore, high maintenance costs are compulsory. In many cases, a perfect appearance is strongly recommended to take measures in order to prevent leakage. However, in China, tunnel waterproof requirements and standards for various special uses are considerably different, such that the basis which engineers apply to design in water-control is insufficient. Especially in montanic region, unpleasant geological condition confines engineers in working out more reasonable methods to stop water seepage, even leakage. In this paper, the current waterproofing requirements and measures in different special tunnels adopted in China are reviewed. The limitations of the popular methods in several practical cases applied to prevent water leakage, such as watertight lining, drainage system, as well as grouting, are analyzed at length. Then, some available measures, regarding concrete lining, watertight layer, drainage establishments as well as casting watertight concrete, are proposed, which we think indispensable for tunnel engineering to efficiently control water seepage and even completely prevent water leakage. In the end, to analyze the seepage field in montanic tunnels, the finite element and boundary element coupling analysis method is presented. As an example, the seepage field in Zhenwushan tunnel of Chongqing is simulated. The calculation results coincide with the in-situ data well, and provide credible evidence for the waterproof measures which will be taken in that tunnel project. The method presented in this paper will save expenditures for surveying measures and will enable more reasonable and reliable waterproofing measures to be taken.     

基于矢量和方法的边坡动力稳定性分析

 边坡矢量和方法是基于力的矢量特性和边坡体真实应力场的分析方法,动力有限元法可模拟得到边坡体在天然地震动荷载作用下每一时刻的应力状态,在此基础上采用边坡矢量和法进行动力稳定性分析,可得到边坡体在地震动过程中的安全系数时程曲线,进而对其动力稳定性进行评价。针对一高陡边坡,在静力稳定性分析的基础上,针对软弱结构面控制的深层滑移面采用矢量和法进行动力稳定性分析,计算中考虑小震(50 a超越概率63%)和大震(50 a超越概率2%)作用下的动力响应。计算结果表明,在小震和大震作用下的动力安全系数分别为1.86,1.66。矢量和法能够较真实地模拟边坡在地震动过程中的动力特征和稳定性状态,为边坡动力稳定性分析提供一种切实可行的分析途径。     

The role of carbon biotemplate density in mechanical properties of biomorphic SiC

Biomorphic SiC was prepared from four types of Mediterranean wood as carbon precursor. Carbon biotemplates were obtained by pyrolysis and carbonization up to 1400 °C and they were infiltrated with liquid silicon in two different directions. A linear correlation between bending strength and bioSiC density for different types of softwood and hardwood has been found. Mechanical properties were modelled according to the MSA (minimum solid area) approach. Fairly good correlation was found when biomorphic SiC is treated as porous solid. Moreover, the fabrication of bioSiC from carbon biotemplates heat-treated up to 2500 °C has been additionally studied. An improvement up to 56% in flexural strength has been reached by densification of bioC at such high temperature.     

Beneficiation of stockpiled fluidized bed coal ash in road base course construction

The presented paper investigates the potential for the utilization of unprocessed, as excavated (i.e. unground), stockpiled coal combustion fluidized bed ash in road base course construction. In addition to functioning as a stabilizer of the fines in the stockpiled material, this ash also permits treating the stockpiled ash agglomerates as an aggregate. Both untreated and cement-treated mix designs were evaluated. The laboratory program included unconfined strength measurements, triaxial, volumetric swell, and moisture susceptibility testing protocols performed on cylindrical specimens compacted at their optimum moisture content.The results have shown that, without breaking down the agglomerates by grinding, the unstabilized stockpiled ash possesses very little residual cementitious activity; whereas, if treated with small amounts of cement (3%), it meets the required strength criteria for cement-treated base courses while minimizing the volumetric swell characteristics.     

Absorption and fluorescence spectra of gallium phosphide（GaP） nanoparticles

The optical absorption spectrum ranging from 200 to 800 nm and fluorescence spectra ranging from 300 to 650 nm of GaP nanoparticles at room temperature were reported. From the optical absorption spectrum it is inferred that the GaP nanoparticles exhibit a direct transition of about 410 nm （3.02 eV） and an indirect transition around 480 nm （2.58 eV）. In addition, an absorption peak at about 308 nm （4.02 eV） corresponding to the direct transition at higher energy was observed. The absorption peak was attributed to the transition from the spin-orbit-split valence band to the lowest conduction band along the A direction. By observing the fluorescence of the GaP nanoparticles, it follows that multiple emission bands corresponding to the violet, blue, and yellow light are shown peaking at about 400.4-414.1 nm （3.097-2.994 eV）, 450.1-466.8 nm （2.755-2.656 eV）, and 582.4 nm （2.129 eV）, respectively. The violet and blue light emissions are ascribed to the direct and indirect transitions from conduction band to valence band of the GaP nanoparticles. As to the weak yellow emission, it may be attributed to the radiative recombination from defect centers. The spin-orbit-splitting of the GaP nanoparticles is determined as about 100 meV.     

平行顶管近接施工的室内试验研究

顶管工程中泥浆护套对顶进中的地层变形与土体劈裂有重要的影响。通过室内试验研究了近距离平行顶管的相互作用。在不同注浆条件下,将顶管顶入布置有两条既有顶管管道的试验箱内,通过测试系统获得不同注浆条件下顶管顶进时顶力的变化情况、土体的竖向变形和顶管顶进对既有顶管管道产生的影响。研究结果显示:顶管顶进过程中,顶力先增大后逐渐减小,土体出现隆起现象;新顶进顶管对既有顶管管道上方土体产生影响,但影响有限;注浆可以有效减小顶管顶进阻力,分布在顶管外壁和周围土体中的浆液使土体体积膨胀,这使得在注浆条件下土体表面产生的变形大于未注浆时土体表面变形。试验结果可以有效地指导近距离平行顶管的施工。