Evaluation of bond using FRP rods with axisymmetric deformations

This paper presents experimental results obtained with the direct pull-out test using machined and wrapped glass/vinylester, carbon/vinylester, and carbon/epoxy FRP rods with axisymmetric lugs. The typical results are given as nominal shear stress vs. free- and loaded-end slip. Experimental results obtained from strain probes used during the pull-out test are presented as shear stress vs. strain. Machined glass/vinylester FRP rods with embedded lengths including five and 10 lugs, and different lug widths and heights were studied. The failure mode consisted of the shearing off of the lugs without concrete damage. Four concrete mixtures with strengths ranging from 32 to 66.1 MPa were examined. Provided that enough confinement is used, it was found that the concrete strength has no noticeable effect on the shear strength and failure mode of FRP rods. Results showed that the FRP–concrete bond is controlled by the lug dimension and shear strength of the resin. The shear strength of the wrapped lugs is less than that of machined ones due to fiber orientation and weaker interfacial bond between the wrapped strands and rod surface.     

Propagation and self-healing properties of Lommel-Gaussian beam through atmospheric turbulence

The superposition of basic non-diffracting beams triggered new research hotspots lately, laying opportunities for long-distance wireless optical communication. The Lommel-Gaussian (LMG) beam formed by the superposition of Bessel-Gaussian light not only possesses non-diffraction feature, but also has tunable symmetry. With the help of Poynting vector analysis, we observed a smaller radial energy flow component during the propagation of the high order symmetrical LMG beam, which allows it to maintain the original beam profile over long distance. Thanks to the energy oscillation of the mainlobe and sidelobes, the mainlobe blocked by the symmetrical LMG beam can be restored. Also, the random phase screen with angular spectrum method is used to describe the beam behaviors in turbulence. The results show that the symmetry LMG is preferred in free space optical communication, and the asymmetric LMG performs poorly due to asymmetric energy transfer.     

Physical limitations of fountain effect pumps

Turbulent He II flow behaviour in superfilters of non-cylindrical shape at large temperature gradients was investigated. It was found that the mass flow rates were always lower than those that would follow from a straightforward extrapolation of results obtained at small temperature gradients; under certain conditions they even went through maxima with respect to the temperature gradient. This is analogous to turbulent classical flow in comparable geometries. Such effects limit the performance of fountain effect pumps and must be taken into account in efficiency calculations.     

Erosion damage of polymeric material by slurry

An attempt was made to reveal the erosion mechanism of a plastic material in slurry containing glass beads of approximately 176 μm in diameter. The experimental observations were interpreted in terms of parameters such as the impact velocity V_p, the impact angle α of the beads and the striking efficiency η. A theoretical flow analysis for a solid-liquid two-phase flow was made and it was found that the trajectories of the particles curved as they approached the specimen, indicating that the actual surface onto which the particles were impinging was much narrower than that which would be expected for sand erosion in an air stream. In the slurry erosion the impact velocity and impact angle differed greatly at different positions of the specimen. This is possibly due to the differences in the density and viscosity of liquid and air. Two distinctly different types of erosion were observed: a typical brittle behaviour occurred near a stagnant point, after an initial incubation period, whereas at a distance from the stagnant point only a slight surface roughness was produced. These two different types of erosion produced a clear boundary. Erosion rates depended on the positions of the specimen and were found to be proportional to (V_p sin α)^2.6. This suggested that the normal component of the impact velocity of the particle determined the erosion rate of the plastic material due to slurry.     

简化增量法计算土钉轴力的模型准确性分析

基于朗肯主动土压力原理的土钉轴力简化增量计算方法虽己广泛应用于工程实践,其模型预测精度尚缺乏系统性评估.鉴于此,本文首先从在中国建造和监测的土钉墙中收集了178根土钉共466个实测土钉轴力数据,建立数据库并进行全面分析,排查异常数据.利用剩下的143根土钉的正常数据,对上述朗肯简化增量法的模型准确性进行评估,并考察3种...     

A numerical simulation of inertial waves in a rotating fluid

Inertial waves in a fluid-filled rotating cylinder are studied using a numerical simulation. A perturbation applied along the centerline at the midplane of a right circular cylinder is used to excite these internal waves. A primitive variable, time-marching finite difference solution of the linearized axisymmetric governing equations is used to obtain the flow and pressure fields. Results compare well with theoretical predictions and are displayed graphically.     

Three-dimensional numerical simulation of air flow around a cubic model by means of large eddy simulation

The unsteady, turbulent flowfield around a cubic model has been simulated by means of large eddy simulation (LES). The resolvable-scale flowfield has been obtained directly by solving the filtered, three-dimensional, time-dependent Navier-Stokes equations. The subgrid-scale motions were simulated by an SGS eddy viscosity model. The computed mean velocity dstributions and various turbulence statistics (i.e. turbulence intensity, velocity spectrum, integral scale, etc.) were compared to those obtained from wind-tunnel experiments to examine the accuracy of LES from the viewpoint of engineering applications. The correspondence between numerical simulation and wind-tunnel experiments is found to be good.     

Polygalacturonase activity in starfruit

Polygalacturonase (PGase) was extracted and partially purified from ripe starfruit (Averrhoa carambola, L.). 2·3- and 7·8-fold purifications were obtained following purification by Amicon ultrafiltration and Sephadex G-100 filtration, respectively. The apparent pH optimum of PGase in the Amicon concentrate and gel filtrate (combined fractions 6–8) was 5·2. Viscometric and reductometric analyses, on PGase in the gel filtrate and paper chromatographic analysis on the enzyme reaction mixture, were carried out to ascertain the mode of action. The results obtained indicated that exoPGase was the only PGase enzyme present in ripe starfruit.     

The Fe3+ role in decreasing the activity of Nafion-bonded IrO2 catalyst for proton exchange membrane water electrolyser

Fe³⁺ is a common ion contaminant for the proton exchange membrane water electrolyser (PEMWE). In this work, three-electrode-system was employed to study the effect of Fe³⁺ on Nafion-bonded IrO₂ catalyst which is conventional anode catalyst for PEMWE. Study results showed that Fe³⁺ contamination decreased IrO₂ catalytic activity significantly only when the following two conditions were both satisfied: 1) Nafion resin exists in working electrode; 2) working electrode potential was over 1.471 V (vs. NHE) which is around the initial voltage of oxygen evolution reaction (OER). Besides, the contaminated working electrode activity was recovered to about 16% by being immersed into 3 M H₂SO₄ solution, but it was recovered to about 59% by ethanol washing method. These study results revealed that Fe³⁺ plays a role of catalyst for H₂O₂ production during OER process, which leads to Nafion resin decomposition. The degradation products covered working electrode surface, and thus decreased effective active sites of IrO₂. Nafion degradation was further confirmed by analyzing 1) F⁻ content in anode water and 2) FTIR of contaminated Nafion membrane.