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Electrospinning of polycarbonate urethane biomaterials

Yakai FENG, Fanru MENG, Ruofang XIAO, Haiyang ZHAO, Jintang GUO

《化学科学与工程前沿（英文）》 2011年第5卷第1期页码 11-18 doi: 10.1007/s11705-010-1011-x

摘要： Polycarbonate urethane (PCU) nano-fibers were fabricated via electrospinning using - dimethylformamide (DMF) and tetrahydrofuran (THF) as the mixed solvent. The effect of volume ratios of DMF and THF in the mixed solvent on the fiber structures was investigated. The results show that nano-fibers with a narrow diameter distribution and a few defects were obtained when mixed solvent with the appropriate volume ratio of DMF and THF as 1∶1. When the proportion of DMF was more than 75% in the mixed solvent, it was easy to form many beaded fibers. The applied voltage in the electrospinning process has a significant influence on the morphology of fibers. When the electric voltage was set between 22 and 32 kV, the average diameters of the fibers were found between 420 and 570 nm. Scanning electron microscopy (SEM) images showed that fiber diameter and structural morphology of the electrospun PCU membranes are a function of the polymer solution concentration. When the concentration of PCU solution was 6.0 wt-%, a beaded-fiber microstructure was obtained. With increasing the concentration of PCU solutions above 6.0 wt-%, beaded fiber decreased and finally disappeared. However, when the PCU concentration was over 14.0 wt-%, the average diameter of fibers became large, closed to 2 μm, because of the high solution viscosity. The average diameter of nanofibers increased linearly with increasing the volume flow rate of the PCU solution (10.0 wt-%) when the applied voltage was 24 kV. The results show that the morphology of PCU fibers could be controlled by electrospinning parameters, such as solution concentration, electric voltage and flow rate.

关键词： electrospinning polycarbonate urethane process parameter average diameter morphology

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细水雾作用下烟颗粒形貌及尺寸变化规律研究

房玉东

《中国工程科学》 2014年第16卷第2期页码 93-100

摘要：

利用Sirion200 型场发射扫描电子显微镜拍摄细水雾作用前后柴油和聚氯乙烯（PVC）材料烟颗粒的形貌和内部结构图像。定义了烟颗粒的采样平均直径（dA）和表面密度（ρS），利用统计分析的方法计算了细水雾作用前后烟颗粒的dA和ρS，研究了采样点空间位置、细水雾工作压力、雾滴粒径和雾滴速度等因素对dA和ρS的影响规律，揭示了细水雾冲刷火灾烟颗粒的主导机理，为细水雾技术用于计算机房等电气环境的火灾烟气抑制提供了科学的参考依据。

关键词：细水雾烟颗粒表面密度采样平均直径

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Performance prediction of switched reluctance generator with time average and small signal models

Jyoti KOUJALAGI, B. UMAMAHESWARI, R. ARUMUGAM

《能源前沿（英文）》 2013年第7卷第1期页码 56-68 doi: 10.1007/s11708-012-0216-8

摘要： This paper presents the complete mathematical model and predicts the performance of switched reluctance generator with time average and small signal models. The complete mathematical model is developed in three stages. First, a switching model is developed based on quasi-linear inductance profile. Next, based on the switching behaviour, a time average model is obtained to measure the difference between the excitation and generation time in each switching cycle. Finally, to track control voltage and current wave shapes, a small signal model is designed. The effectiveness of the complete multilevel model combining electrical machine, power converter, load and control with programming language is demonstrated through simulations. A PI controller is used for controlling the voltage of the generator. The results presented show that the controller exhibits accurate tracking control of load voltage under different operating conditions. This demonstrates that the proposed model is able to perform an accurate control of the generated output voltage even in transient situations. The simulation is performed to choose the control parameters and study the performance of switched reluctance generator prior to its actual implementation. Initial experimental results are presented using NI-Data acquisition card to control the output power according to load requirements.

关键词： generator reluctance switching model small signal model time average model

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A case study on sample average approximation method for stochastic supply chain network design problem

Yuan WANG, Ruyan SHOU, Loo Hay LEE, Ek Peng CHEW

《工程管理前沿（英文）》 2017年第4卷第3期页码 338-347 doi: 10.15302/J-FEM-2017032

摘要： This study aims to solve a typical long-term strategic decision problem on supply chain network design with consideration to uncertain demands. Existing methods for these problems are either deterministic or limited in scale. We analyze the impact of uncertainty on demand based on actual large data from industrial companies. Deterministic equivalent model with nonanticipativity constraints, branch-and-fix coordination, sample average approximation (SAA) with Bayesian bootstrap, and Latin hypercube sampling were adopted to analyze stochastic demands. A computational study of supply chain network with front-ends in Europe and back-ends in Asia is presented to highlight the importance of stochastic factors in these problems and the efficiency of our proposed solution approach.

关键词： supply chain network stochastic demand sampling average approximation Bayesian bootstrap Latin hypercube sampling

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Experimental study on average movement characteristics of bed-load particles

Limo TANG, Xingkui WANG,

《结构与土木工程前沿（英文）》 2009年第3卷第4期页码 435-439 doi: 10.1007/s11709-009-0050-1

摘要： The three-dimensional movements of bed-load particles in an open channel with different grain diameters and different specific gravities under the conditions of different hydraulic gradient are measured by means of particle tracking velocimetry (PTV) technique. The average movement characteristics of the particles are analyzed by statistics. The results show that the longitudinal average velocities of the particles neither agree with the law suggested by Einstein nor obey the law assumed by Bagnold. Einstein’s law is that the particle velocity is equal to 11.6 times of shear velocity, and the Bagnold’s law assumes the velocity equal to the difference between flow velocity at corresponding water depth and settling velocity of particle. Two formulas for determining the velocity of particle in the forms of expression given by Einstein and Bagnold are obtained according to the statistical results of experimental data, respectively.

关键词： different longitudinal three-dimensional particle Bagnold

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Investigation of bubble diameter and flow regime between water and dilute aqueous ethanol solutions in

Baharak SAJJADI, Mostafa Keshavarz MORAVEJI, Reza DAVARNEJAD

《化学科学与工程前沿（英文）》 2011年第5卷第2期页码 194-202 doi: 10.1007/s11705-010-1019-2

摘要： In this study, the effect of ethanol addition into pure water and its concentration on bubble diameter, gas hold-up and flow regimes were investigated in an airlift reactor. Air and water with ethanol (concentration ranging from 0%–1%, v/v) were as dispersed and continuous phases, respectively. Superficial gas velocity was considered as an effective parameter. Bubble size distribution was measured by photography and picture analysis at various concentrations of ethanol and various velocities of gas. Alcohol concentration enhancement caused bubble diameter to decrease. Furthermore, the bubbles diameter in pure water was nearly 4 times higher than that of ethanol with concentration of 1% (v/v) and also was 3.4 times higher than that of ethanol with concentration of 0.25% (v/v) at the highest aeration gas velocity inlet. For ethanol solutions in lower superficial gas velocity, a homogenous flow regime was observed. This trend continued to inlet gas velocity of about 0.4 cm/s. The transition flow regime occurred after this datum although in pure water, a homogenous flow regime was observed up to a superficial gas velocity of 0.7 cm/s. The gas hold-up in dilute ethanol solutions were more than (around 2 times) that of pure water and increased with increasing concentration of ethanol in those solutions.

关键词： airlift rector bubble diameter gas hold-up flow regime ethanol

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Accounting for the uncertainties in the estimation of average shear wave velocity using – correlations

《结构与土木工程前沿（英文）》 2021年第15卷第5期页码 1199-1208 doi: 10.1007/s11709-021-0749-1

摘要： Site-specific seismic hazard analysis is crucial for designing earthquake resistance structures, particularly in seismically active regions. Shear wave velocity ( V _S) is a key parameter in such analysis, although the economy and other factors restrict its direct field measurement in many cases. Various V _S–SPT– N correlations are routinely incorporated in seismic hazard analysis to estimate the value of V _S. However, many uncertainties question the reliability of these estimated V _S values. This paper comes up with a statistical approach to take care of such uncertainties involved in V _S calculations. The measured SPT– N values from all the critical boreholes were converted into statistical parameters and passed through various correlations to estimate V _S at different depths. The effect of different soil layers in the boreholes on the Vs estimation was also taken into account. Further, the average shear wave velocity of the top 30 m soil cover ( V _S30) is estimated after accounting for various epistemic and aleatoric uncertainties. The scattering nature of the V _S values estimated using different V _S– N correlations was reduced significantly with the application of the methodology. Study results further clearly demonstrated the potential of the approach to eliminate various uncertainties involved in the estimation of V _S30 using general and soil-specific correlations.

关键词： uncertainties V _S– N correlations V _S30 SPT data statistical methodology

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Impacts of different diameter combinations on the temperature of a crude oil pipeline when colocating

Bo YU, Yue SHI, Xin LIU, Jinjun ZHANG, Jinjia WEI,

《能源前沿（英文）》 2010年第4卷第2期页码 192-197 doi: 10.1007/s11708-009-0074-1

摘要： In order to show the effects of different diameter combinations on crude oil temperature when a crude oil pipeline and a products pipeline are laid in one trench, four typical diameter combinations are selected to conduct numerical simulation. After a series of calculations, the minimum mean temperature difference and the maximum temperature difference of the crude oil along the pipelines are obtained. In real pipeline constructions, the effects of other diameter combinations on crude oil temperature can be predicted by the method of linear interpolation to calculate results of the four diameter combinations obtained in this study.

关键词： technology of laying two pipelines in one trench diameter combinations crude oil temperature pipeline interval

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Effects of slip length and hydraulic diameter on hydraulic entrance length of microchannels with superhydrophobic

Wenchi GONG, Jun SHEN, Wei DAI, Zeng DENG, Xueqiang DONG, Maoqiong GONG

《能源前沿（英文）》 2020年第14卷第1期页码 127-138 doi: 10.1007/s11708-020-0661-8

摘要： This paper investigated effects of slip length and hydraulic diameter on the hydraulic entrance length of laminar flow in superhydrophobic microchannels. Numerical investigations were performed for square microchannels with Re ranging between 0.1 and 1000. It is found that superhydrophobic microchannels have a longer hydraulic entrance length than that of conventional ones by nearly 26.62% at a low Re. The dimensionless hydraulic entrance length slightly increases with the increasing slip length at approximately Re<10, and does not vary with the hydraulic diameter. A new correlation to predict the entrance length in square microchannels with different slip lengths was developed, which has a satisfying predictive performance with a mean absolute relative deviation of 5.69%. The results not only ascertain the flow characteristics of superhydrophobic microchannels, but also suggest that super hydrophobic microchannels have more significant advantages for heat transfer enhancement at a low Re.

关键词： laminar flow hydraulic entrance length super hydrophobic surface slip length hydraulic diameter

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大直径管片拼装及缺陷处理

程学武,许维青,杨志永

《中国工程科学》 2010年第12卷第12期页码 89-93

摘要：

总结了北京地下直径线工程大直径盾构管片拼装技术，初步分析了大直径盾构钢筋混凝土管片施工过程中的表观破损原因，并对破损管片修补技术进行探讨，提出对拱腰以上、拱腰以下部位管片的不同修补方法，保证了大直径盾构管片的强度及外观质量。

关键词：大直径盾构管片拼装修补

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Stability analysis of large diameter thin-walled tube beam-columns

PAN Hanming, GUO Yanlin, LIANG Shuo, PEI Shengxing, LIANG Weisheng, WANG Lewen

《结构与土木工程前沿（英文）》 2008年第2卷第2期页码 123-132 doi: 10.1007/s11709-008-0017-7

摘要： Based on a blind spot in the current design standard of steel structures, the large diameter thin-walled tube beam-columns are analyzed using nonlinear finite element method in this paper. The influence of several factors on stability capacity of the large diameter thin-walled tube beam-columns is taken into account. Thus, according to the correlative design standard of steel structures, and on the basis of the numerical analytical results by the finite element methods, the calculation formulas of the stability bearing capacity are presented for beam-column members of the large diameter thin-walled tubes. Three tests of thin-walled steel tube beam-columns were reported. Test results for deformations and ultimate strength are found to be in a good agreement with the corresponding values predicted by the calculation formulas, and the proposed methods can be used in design practice.

关键词： ultimate strength nonlinear numerical analytical diameter thin-walled practice

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Influence of sprinkler irrigation droplet diameter, application intensity and specific power on flower

Yisheng ZHANG, Delan ZHU

《农业科学与工程前沿（英文）》 2017年第4卷第2期页码 165-171 doi: 10.15302/J-FASE-2017145

摘要： To determine the main parameters of droplet strike damage and avoid flower injury due to the unsuitable practices during sprinkler irrigation, an indoor experiment of irrigation droplet impact on cyclamen was conducted. The influences of different parameters such as droplet diameter, application intensity, specific power on flower strike damage was analyzed using Image Pro-Plus software to compute strike damage area and define damage level by sense-analysis. The results showed that a damage area of <1% represents a safe irrigation level, 1%–3% slight damage level, 3%–6% moderate damage level, and>6% heavy damage level. Equations of application intensity, specific power with sprinkler irrigation time and flower injury ratio were regressed against parameters which cause impact damages. The results indicated that specific power has a significant correlation with injury, and flower damage area increased as the increasing of the value of specific power for the same irrigation time. Application intensity was also correlated with injury when the droplet diameter was larger than 1 mm. When the duration of sprinkler irrigation was 1, 5 and 10 min, the threshold of impinging damage of application intensity was 25.30, 5.01 and 1.64 mm·h and the specific power was 0.467×10 , 9.340×10 and 3.110×10 W·m . These results provide a reference for determining the suitable values of sprinkler properties in operation design.

关键词： application intensity damage floriculture flowers specific power sprinkler irrigation

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A new performance evaluation method and its application in fin-tube surface design of small diameter

Jufang FAN, Weikun DING, Zhigeng WU, Yaling HE, Wenquan TAO, Yongxin ZHENG, Yifeng GAO, Ji SONG

《能源前沿（英文）》 2011年第5卷第1期页码 59-68 doi: 10.1007/s11708-010-0132-8

摘要： In this paper, a simple yet efficient performance comparison method is proposed based on the assumptions of constant properties and identical frontal area. For this method, no correlations are required, and a small number of discrete data are sufficient. To illustrate the feasibility of the proposed approach, a new slotted fin with 4 mm tubes is designed to replace the original louvered fin with tubes of 7 mm. The orthogonal design method is adopted in the fin design to reduce the number of computational cases significantly, and yet a nearly optimum combination of major geometric factors can still be obtained. The reasonable parametric combination of 3 global parameters is obtained by analyzing the numerical results of 16 plain plate fins. Based on this result, 3 new slotted fins with different fin pitches are studied. The slotted fin with a fin pitch of 1.4 mm is recommended after considering the heat transfer, comprehensive performance, and cost of material and operation. The result shows that compared with the original louvered fin, the recommended fin not only increases the heat transfer rate by 2.2%, 22.5%, and 13.7% under an identical flow rate, identical pressure drop, and identical pumping power constraint, respectively, but also saves approximately 36% of the copper tube materials.

关键词： performance evaluation orthogonal design small-diameter tube

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北京铁路地下直径线泥水盾构刀盘、刀具适应性分析

何峰,李小岗,孙善辉

《中国工程科学》 2010年第12卷第12期页码 35-40

摘要：

结合北京站至北京西站地下直径线工程实例，通过不同盾构刀盘刀具配置在砂卵石下的应用对比，重点对工程刀盘刀具改造前后对地层的适应性进行了详细的对比分析，提出了砂卵石条件下刀盘刀具配置应注意的关键问题，对类似工程有借鉴作用。

关键词：直径线泥水盾构刀盘刀具适应性

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Cutting Force Model for a Small-diameter Helical Milling Cutter

LI Xiwen, YANG Shuzi, YANG Mingjin, XIE Shouyong

《机械工程前沿（英文）》 2007年第2卷第3期页码 272-277 doi: 10.1007/s11465-007-0047-1

摘要： In the milling process, the major flank wear land area (two-dimensional measurement for the wear) of a small-diameter milling cutter, as wear standard, can reflect actual changes of the wear land of the cutter. By analyzing the wearing characteristics of the cutter, a cutting force model based on the major flank wear land area is established. Characteristic parameters such as pressure parameter and friction parameter are calculated by substituting tested data into their corresponding equations. The cutting force model for the helical milling cutter is validated by experiments. The computational and experimental results show that the cutting force model is almost consistent with the actual cutting conditions. Thus, the cutting force model established in the research can provide a theoretical foundation for monitoring the condition of a milling process that uses a small-diameter helical milling cutter.

关键词： computational corresponding helical milling theoretical foundation Characteristic