Measurement of Liquid Concentration Fields Near Interface with Cocurrent Gas-Liquid Flow Absorption Using Holographic Interferometry

Real-time laser holographic interferometry was applied to measure liquid concentrations of CO2 in the vicinity of gas-liquid free interface under the conditions of cocurrent gas-liquid flow for absorption of CO2 by ethanol. The influences of the Reynolds number on the measurable interface concentration and on the film thickness were discussed. The results show that CO2 concentration decreases exponentially along the mass transfer direction,and the concentration gradient increases as Reynolds number of either liquid or gas increases. CO2 concentrations fluctuate slightly along the direction of flow; on the whole, there is an increase in CO2 concentration. The investigation also demonstrated that film thickness decreases with the increase of Reynolds number of either of the two phases. Sherwood number representing the mass transfer coefficient was finally correlated as a function of the hydrodynamic parameters and the physical properties.

Exact solution of plane isolated crack normal to a bimaterial interface of infinite extent

This paper presents an exact solution for the transverse interface crack in the plane strain case. The crack is perpendicular to the interface and in one material. The exact complex stress functions are first obtained with some unknown constants. The satisfactions of all boundary conditions are then checked, the condition at infinity is considered and the unknown constants are determined. Further study may focus on the case with different shear moduli and the influence of the large deformation.

Growth and aggregation micromorphology of natural gas hydrate particles near gas-liquid interface under stirring condition

To investigate the morphological evolution of the whole growth and aggregation processes of hydrate crystals near the gas–liquid interface,we used a high-pressure visual reactor with high-speed camera to capture the micromorphology of hydrate particles in a natural gas+pure water system with pressure from 2.6 to 3.6 MPa and sub-cooling from 4.7 to 6.23C.The results showed that under low sub-cooling conditions,the amount and size of particles increased first and then decreased in the range of 0–330 lm,and the small particles always dominated.These particles can be roughly classified into two categories:planar flake particles and polyhedral solid particles.Then,the concept of maximum growth dominant particle size was proposed to distinguish the morphological boundary of growth and aggregation.In addition,the micro model was established to better reflect the effects of particle formation process and evolution mechanism near the gas–liquid interface under stirring condition.The results of this study can provide a guidance for flow assurance in multiphase pipeline.

THE SCATTERING OF GENERAL SH PLANE WAVE BY INTERFACE CRACK BETWEEN TWO DISSIMILAR VISCOELASTIC BODIES

The scattering of general SH plane wave by an interface crack between two dissimilar viscoelastic bodies is studied and the dynamic stress intensity factor at the crack-tip is computed. The scattering problem can be decomposed into two problems: one is the reflection and refraction problem of general SH plane waves at perfect interface (with no crack); another is the scattering problem due to the existence of crack. For the first problem, the viscoelastic wave equation, displacement and stress continuity conditions across the interface are used to obtain the shear stress distribution at the interface. For the second problem, the integral transformation method is used to reduce the scattering problem into dual integral equations. Then, the dual integral equations are transformed into the Cauchy singular integral equation of first kind by introduction of the crack dislocation density function. Finally, the singular integral equation is solved by Kurtz's piecewise continuous function method. As a consequence, the crack opening displacement and dynamic stress intensity factor are obtained. At the end of the paper, a numerical example is given. The effects of incident angle, incident frequency and viscoelastic material parameters are analyzed. It is found that there is a frequency region for viscoelastic material within which the viscoelastic effects cannot be ignored.

ELASTIC-PLASTIC CRACK GROWTH ON PLANE STRAIN BIMATERIAL INTERFACE

Finite element computations are carried out to simulate plane strain crack growth on a bimaterial interface under the assumption of small scale yielding.The modified Guron constitutive equation and the element vanish technique introduced by Tvergaard et al.are used to model the final formation of an open crack.It is found from the calculation that the critical fracture toughness for crack growth is much low- er in bimaterials than that in homogeneous material.The critical fracture toughness is strongly dependent on material properties of the bimaterial pair and the mixed mode of remote loads.The interface crack grows in the more compliant(lower hardening)material or in the weaker(lower yield strength)material.In Mode-Ⅰ loading,the crack grows zigzag along the interface.

Measurement of Liquid Concentration Fields Near Interface with Cocurrent Gas-Liquid Flow Absorption Using Holographic Interferometry

Real-time laser holographic interferometry was applied to measure liquid concentrations of CO2 in the vicinity of gas-liquid free interface under the conditions of cocurrent gas-liquid flow for absorption of CO2 by ethanol. The influences of the Reynolds number on the measurable interface concentration and on the film thickness were discussed. The results show that CO2 concentration decreases exponentially along the mass transfer direction, and the concentration gradient increases as Reynolds number of either liquid or gas increases. CO2 concentrations fluctuate slightly along the direction of flow; on the whole, there is an increase in CO2 concentration. The investiga- tion also demonstrated that film thickness decreases with the increase of Reynolds number of either of the two phases. Sherwood number representing the mass transfer coefficient was finally correlated as a function of the hy- drodynamic parameters and the physical properties.

ANTI-PLANE CRACK MOVING ALONG THE INTERFACE OF DISSIMILAR PIEZOELECTRIC MATERIALS

The problem of an anti-plane Griffith crack moving along the interface of dissimilar piezoelectric materials is solved by using the integral transform technique. It is shown from the result that the intensity factors of anti-plane stress and electric displacement around the crack tip are dependent on the speed of the Griffith crack as well as the material coefficients. When the two piezoelectric materials are identical, the present result will be reduced to the result far the problem of an anti-plane moving Griffith crack in homogeneous piezoelectric materials.

Adsorption structures of frothers at gas–liquid interface using DFT method

Density functional theory (DFT) simulation was performed to investigate the adsorption mechanisms between frothers and gas–liquid interface. In water phase, the polar head group of the frother molecule was connected with water molecules by hydrogen bonding, while the non-polar group showed that hydrophobic property and water molecules around it were repelled away. The adsorption of water molecules on single frother molecule suggests that the complexes of α-terpineol-7H2O, MIBC-7H2O and DF200-13H2O reach their stable structure. The hydration shell affects both the polar head group and the non-polar group. The liquid film drainage rate of DF200 is the lowest, while α-terpineol and MIBC are almost the same. The adsorption layer of frother molecules adsorbed at the gas-liquid interface reveals that the α-terpineol molecules are more neatly arranged and better distributed. The DF200 molecules are arranged much more loosely than MIBC molecules. These results suggest that the α-terpineol molecule layer could better block the diffusion of gas through the liquid film than DF200 and MIBC. The simulation results indicate that the foam stability of α-terpineol is the best, followed by DF200 and MIBC.

Analysis of mode Ⅲ crack perpendicular to the interface between two dissimilar strips

The present work is concerned with the problem of mode Ⅲ crack perpendicular to the interface of a bi-strip composite. One of these strips is made of a functionally graded material and the other of an isotropic material, which contains an edge crack perpendicular to and terminating at the interface. Fourier transforms and asymptotic analysis are employed to reduce the problem to a singular integral equation which is numerically solved using Gauss-Chebyshev quadrature formulae. Furthermore, a parametric study is carried out to investigate the effects of elastic and geometric characteristics of the composite on the values of stress intensity factor.

Simulation of Air-Water Interface Effects for High-speed Planing Hull

High-speed planing crafts have successfully evolved through developments in the last several decades.Classical approaches such as inviscid potential flow–based methods and the empirically based Savitsky method provide general understanding for practical design.However,sometimes such analyses suffer inaccuracies since the air–water interface effects,especially in the transition phase,are not fully accounted for.Hence,understanding the behaviour at the transition speed is of fundamental importance for the designer.The fluid forces in planing hulls are dominated by phenomena such as flow separation at various discontinuities viz.,knuckles,chines and transom,with resultant spray generation.In such cases,the application of potential theory at high speeds introduces limitations.This paper investigates the simulation of modelling of the pre-planing behaviour with a view to capturing the air–water interface effects,with validations through experiments to compare the drag,dynamic trim and wetted surface area.The paper also brings out the merits of gridding strategies to obtain reliable results especially with regard to spray generation due to the air–water interface effects.The verification and validation studies serve to authenticate the use of the multi-gridding strategies on the basis of comparisons with simulations using model tests.It emerges from the study that overset/chimera grids give better results compared with single unstructured hexahedral grids.Two overset methods are investigated to obtain reliable estimation of the dynamic trim and drag,and their ability to capture the spray resulting from the air–water interaction.The results demonstrate very close simulation of the actual flow kinematics at steady-speed conditions in terms of spray at the air–water interface,drag at the pre-planing and full planing range and dynamic trim angles.

低界面热阻、高面外热导率纤维素基复合膜

为有效解决电子设备的高效散热问题,迫切需要开发高性能导热复合材料。近年来,具有高面内热导率的导热复合膜已经取得了很大的进展,但低的面外热导率限制了其应用。在实际应用中,具有高面内和面外热导率的导热复合膜表现出均匀的散热性能,是先进电子器件理想的热管理材料。依据“最密堆积模型”,分别使用球形Al_(2)O_(3)粒子和石墨烯微片(GNPs)作为导热模板和导热增强相,采用真空辅助自组装方法,通过填料立体有序结构设计和界面结构优化,制备了高面外热导率柔性细菌纤维素(BC)基导热复合膜材料。大尺寸Al_(2)O_(3)粒子构筑基础传热网络,少量小尺寸Al_(2)O_(3)粒子填充在大尺寸Al_(2)O_(3)粒子之间的间隙,GNPs以球形Al_(2)O_(3)粒子为模板进行有序排列;通过调节不同尺寸Al_(2)O_(3)粒子的比例和对导热填料进行聚多巴胺(PDA)表面改性,构建了具有低界面热阻的协同立体传热网络,制备的导热复合膜的面外和面内热导率分别达到5.42 W/(m·K)和7.06 W/(m·K)。导热填料的PDA表面改性增强了填料/基体之间相互作用,在提高复合材料导热性能的同时也改善了力学性能,复合材料的断裂强度和断裂伸长率均得以提升。

全功率型逆变电源侧工频变化量距离保护性能下降机理分析

受逆变型分布式电源(IIDG)系统内阻抗不稳定的影响,工频变化量距离保护在全功率型逆变电源侧存在拒动风险,但现有理论未能从机理方面明确指出造成内阻抗不稳定的具体因素,难以提出针对性的保护改进方案。为了深入探究IIDG侧工频变化量距离保护性能急剧下降的机理,基于阻抗平面法分析指出,在全功率型逆变电源控制策略的作用下,IIDG侧正序电流增量表现为相位、幅值受控的独立变量,其与过渡电阻共同构成的附加阻抗大小随故障工况变化且矢量方向发生不确定性偏转,导致保护正确动作可行域不明晰,在传统阻抗继电器整定判据下保护可靠性严重劣化。在此基础上,进一步研究了主流的PQ控制及低电压穿越控制策略对该保护动作安全性和耐受过渡电阻能力的影响。基于PSCAD/EMTDC的仿真结果验证了理论分析的正确性,为工频变化量距离保护在IIDG并网工况下故障响应能力的恢复提供了有益的理论参考。

新一代高速动车组平面布局及旅客界面设计

高速铁路是人民群众出行的重要交通工具,随着国家经济的发展和国民生活水平的提高,人们对提升铁路出行服务品质、满足需求多样化存在迫切需求。通过调研国内外高速铁路行业列车平面布局及旅客服务界面,基于车上设施、给水卫生系统、车内环境控制系统等旅客服务设施的关联关系,总结新一代高速动车组平面布局和旅客界面设计原则,基于面向旅客的服务界面需求,深入研究客室布置、餐饮服务设施、给水卫生服务设施的多样化、多功能、智能化、人性化设计方案,提出面向旅客的新一代高速动车组平面布局及旅客服务界面设计方案建议。

The Mechanism of Interfacial Mass Transfer in Gas Absorption Process

Based on the method of molecular thermodynamics, the mass transfer mechanism at gas-liquid interface is studied theoretically, and a new mathematical model is proposed. Using laser holographic interference technique, the hydrodynamics and mass transfer characteristics of CO2 absorption are measured. It is shown that the calculated results are in good agreement with the experimental data.

Radio Access Network Slicing Based on C/U Plane Separation

Network slicing achieves many interests from industry and academics due to its flexibility and scalability.In this paper,we present a novel slicing scheme for radio access networks(RANs) based on control/user(C/U) plane separation.Firstly,we divide e NBs into two sub-e NBs called Ce NB and Ue NB,for transmitting control data and user data respectively,thereby facilitating C/U plane separation.Secondly,upon Ce NBs and Ue NBs being virtualized,we develop two RAN slices for control and user plane respectively.Experimental results show the feasibility of the proposed scheme.

Novel Stitched Ground Plane Optimizations for Microstrip Patch Antennas at Wi-Fi and WiMAX Applications

This work explores the optimal mesh structure, stitch density and production technique of stitched ground plane for microstrip patch antenna. Meshed ground plane was used as a generic problem. A stitched ground plane is pro-posed and designed using Matlab interface to computer embroidery. Using the meshed or stitched ground plane as a case study, the resistance between meshes was analysed and measured. The equivalent resistance between nodes is a function of their distance apart. A finite resistive grid was simulated and compared to measured sets of data. A microstrip patch antenna with stitched ground shows comparable performance to the conventional etched ground of the size in terms of bandwidth. The stitched ground plane has a higher band-width than the etched copper ground plane because of the increased thickness of the substrate. Thus, it can be concluded that the use of the interface method shows the possibilities of controlling the stitch density and distances between mesh nodes. The interface increases the stitching density and reduces the elec-trical resistance between mesh nodes making the antennas flexible and weara-ble. The functionality of these antenna samples has been tested and validated using microstrip patch ground at 2.45 GHz and 5 GHz. Measurement results on the proposed stitched ground planes were compared with the theory of infinite resistive network that shows good agreement.

PROBLEMS OF COLLINEAR CRACKS BETWEEN BONDED DISSIMILAR MATERIALS UNDER ANTIPLANE CONCENTRATED FORCES

In this paper problems of collinear cracks between bonded dissimilar materials under antiplane concentrated forces are dealt with. General solutions of the problems are formulated by applying extended Schwarz principle integrated with the analysis of the singularity of complex stress functions. Closed-form solutions of several typical problems are obtained and the stress intensity factors are given. These solutions include a series of original results and some results of previous researches. It is found that under symmetrical loads the solutions for the dissimilar materials are the same as those for the homogeneous materia[7]

回字形3D打印混凝土受压性能试验及数值模拟

本文将回字形3D打印混凝土试样切割成中心回字型、边缘条纹型和角部拐角型三种类型试块,开展X、Y和Z三个方向的抗压强度试验,并利用基于界面黏结的有限元模型模拟其受压行为,探究回字形3D打印混凝土的强度不均匀性、各向异性和形成机理。结果表明:三种类型试块均为X向(顺打印条带方向)抗压强度最高,Z向(逐层叠加方向)强度最小,其中,中心回字型试块三个方向的平均强度最高,各向异性也最显著,但总体而言三种类型试块的平均强度差异不大;有限元模型的强度计算结果及损伤特征与试验结果基本吻合,说明黏结单元的引入能较好地模拟3D打印混凝土的界面行为;与受力方向垂直的水平界面对强度影响较大,不同加载方向上此类界面的数量和分布不同是导致3D打印混凝土强度各向异性的主要原因。上述研究为3D打印混凝土的打印路径规划提供了参考。

压电双材料反平面问题的界面裂纹分析

文中研究了压电双材料在反平面载荷和平面内电载荷共同作用下的电弹场,运用边界配置法求解xoy平面为各向同性面的压电双材料在2种加载情况下的应力强度因子和能量释放率,并根据界面应力强度因子和能量释放率数值计算方法分析了材料尺寸比例、电位移D0、弹性模量、配点数及幂级数项数对应力强度因子和能量释放率的影响,得到了相应的关系变化曲线图。结果表明:在裂尖处应力具有1/2阶的奇异性;材料厚度越小裂纹长度越长,应力强度因子和能量释放率越大;能量释放率随材料弹性模量的增大而减小;配点数和幂级数项数对应力强度因子和能量释放率的影响不大,但随着配点数和幂级数项数增多数值趋于稳定,且更接近真实值。当配点数在35时,应力强度因子和能量释放率都趋于稳定,而幂级数项数分别在35、22时应力强度因子和能量释放率趋于稳定;当应力强度因子和能量释放率与外加电位移在加载情况不同时,有不同的曲线关系;该方法能够方便地计算多种加载情况下压电双材料裂尖的应力强度因子和能量释放率,能反映压电双材料的界面损伤特性,有利于压电智能结构在各行业应用推广。