The Effect of Sudden Change in Pipe Diameter on Flow Patterns of Air-Water Two-Phase Flow in Vertical Pipe (Ⅱ) Sudden-Expansion Cross-Section

In this companion paper, flow patterns in the upstream and downstream tubes of a sudden-expansion cross-section (SECS) in a vertical straight pipe were presented. The effect of SECS on flow patterns upstream and downstream was analyzed by comparing with flow patterns in uniform cross-section vertical tubes. It is found the effect is great. There exist great instabilities of two-phase flow in the neighboring areas of the SECS both downstream and upstream.

The Effect of Sudden Change in Pipe Diameter on Flow Patterns of Air-Water Two-Phase Flow in Vertical Pipe (I) Sudden-Contraction Cross-Section

Flow patterns upstream and downstream of a sudden-contraction cross-section in a vertical straight pipe were presented. By comparing with flow patterns in uniform cross-section vertical tubes, the effect of the sudden change in pipe diameter on flow patterns was analyzed. Flow pattern transition mechanisms were discussed and transition criteria for flow pattern transitions were deduced accordingly using the dimensional analysis.

The Optimal Cross-section Design of the “Trapezoid-V” Shaped Drainage Canal of Viscous Debris Flow

Debris flow drainage canal is one of the most widely used engineering measures to prevent and manage debris flow hazards.The shape and the sizes of the cross-section are important parameters when design debris flow drainage canal.Therefore,how to design the appropriate shape and sizes of the cross-section so that the drainage canal can have the optimal drainage capacity is very important and few researched at home and abroad.This study was conducted to analyze the hydraulic condition of a Trapezoid-V shaped drainage canal and optimize its cross-section.By assuming characteristic sizes of the cross-section,the paper deduced the configuration parameter of the cross-section of a Trapezoid-V shaped debris flow drainage canal.By theory analysis,it indicates that the optimal configuration parameter is only related to the side slope coefficient and the bottom transverse slope coefficient.For this study,the Heishui Gully,a first-order tributary of the lower Jinsha River,was used as an example to design the optimal cross-section of the drainage canal of debris flow.

HYBRID PERTURBATION-GALERKIN SOLUTION OF THE FLOW IN A CIRCULAR CROSS-SECTION TUBE WITH CONSTRICTION

Using hybrid perturbatin_Galerkin technique,a crcular cross_section tube model with sinusoidal wall is studied.This technique can remove the limitation of small parameters for perturbation and the difficulty of selecting good coordinate functions about Galerkin technique.The effects caused by the boundary conditions and the Reynolds number on the flow were discussed.The position of the separate and reattachment points was obtained.The tendency of the variation about the shear stress on the wall and friction factor along the axis direction were also analyzed.The results at a small parameter have good agreements with the perturbation ones.

Modeling Blood Flow in Veins of Uniform Properties (Giraffe Jugular Vein)

This paper models the giraffe’s jugular veins as a uniform collapsible tube from a rigid skull. The equations governing one-dimensional steady flow through such a tube for various conditions have been developed. The effects of inertial and inclination angles that have not been discussed previously have been included. It has been shown that different flows for a uniform tube (vein) are possible. However, this flow matches that of a jugular vein which is supercritical, and the steady solution has been given by the balance between the driving forces of gravity and the viscous resistance to the flow at the right atrium of the heart must be sub-critical for a fixed right-atrium pressure which means that an elastic jump is required to return the flow to sub-critical from the supercritical flow upstream this type of relationship gives rise to flow limitation at the same time given any right atrium fixed pressure there exists a maximum flow rate which when exceeded the boundary conditions of the flow do not hold boundary conditions at the right atrium are not satisfied hence making the steady flow impossible this mechanism of flow limitation is slightly different from the other one in that causes airways through forced expiration from the observation made it is clearly shown that there is an intravascular pressure difference with a change in height.

Flow patterns and their transition characteristics of the air-water two-phase flow in a horizontal pipe with a sudden-changed cross-section area

Flow patterns in upstream and downstream straight tubes of sudden-changed areas in a horizontal straight pipe were experimentally examined. Both sudden-expansion cross-section (SECS) and sudden-contraction cross-section (SCCS) were investigated. The flow pattern maps upstream and downstream were delineated and compared with those in straight tubes with uniform cross-sections. The effects of the SECS and SCCS on flow patterns were discussed and analyzed. Furthermore, flow pattern transition mechanisms resulting in occurrences of different flow patterns were simply discussed and some transition criteria for the flow pattern transitions were deduced by using the non-dimensionlized analysis method.

MAGNETOHYDRODYNAMIC PIPE FLOW IN DUCTS WITH PARTIAL CIRCULAR RING CROSS SECTION AND ANNULAR CROSS SECTION

In this paper we use the Green function method to solve the problem of steady one dimensional flow of an incompressible viscous, electrically conducting fluid through a pipe with partial circular ring cross sec- tion and one with annular cross section, in the presence of an applied transverse uniform magnetic field, We ob- tain analytic solutions and carry out some numerical calculations of the velocity distribution and induced magnet- ic field.

溃坝洪水演进一维水动力模型

中国是受洪水灾害影响最严重的国家之一。洪水数值模型可准确地反映洪水的演进与致灾过程。本研究针对天然河道洪水过程存在的尺度大、水流流态复杂、河道断面形式多变以及计算建模困难等问题,提出一套基于Godunov格式的有限体积法离散圣维南方程组的一维水动力模型,并采用求解复杂断面水力要素之间关系的方法,提高了一维水动力模型求解的精度与效率,精确地反映了复杂断面河道的水流运动特性。将模型模拟得到的数值解与算例中的解析解或实测数据进行对比,结果表明:(1)构建的一维水动力模型模拟结果与理想算例解析解及实验实测数据吻合程度均较高,所有算例的E NS均大于0.5,说明模型具有良好的稳定性和适应性;(2)将模型应用至金沙江白格堰塞湖溃坝洪水算例中,模拟得到的流量峰值及整体洪水过程均与实测过程吻合较好,在叶巴滩和苏洼龙两个测点处E NS分别为0.633和0.812,证明了模型在实际应用中的适用性与可靠性。结果表明,开发的一维水动力模型对溃坝洪水等水流流态复杂、突发性强的洪水过程具有良好的模拟效果。本研究可为河道及溃坝洪水风险的初步、快速评估等工作提供有效的模拟支撑。

金鸡滩二线船闸工程原型观测方法

水利枢纽船闸改扩建是内河航道整治工程中的控制性工程,以右江金鸡滩水利枢纽二线船闸工程原型观测实践为例,对船闸改扩建原型观测的方法进行分析和总结,主要包括比降观测、表面流速流向测量、断面流量和流速流向观测、泥沙测验和底质取样等5个观测方法。通过现场实践生产,在枢纽上下游多维度同步观测和采样,并对观测成果进行统计、分析和研究,为枢纽船闸改扩建的规划、设计和施工等建设技术方案提供水文基础资料,为模型试验、航道整治工程提供准确的工程实施数据,值得类似项目借鉴和应用。

基于煤流检测实现带式输送机节能运行控制

为解决当前带式输送机工频运行存在小煤流量时电能浪费的问题,在对输送带煤流检测基本原理分析的基础上,提出了以激光直射三角测距原理为基础的煤流检测系统,进而换算得出输送带的实时煤流量;其次,根据实时煤流量的预期带速和实时带速的偏差值基于模糊控制器实现对输送机的节能控制。

清原满族自治县红河水污染风险防范及应急达标措施研究

本文调查了清原红河水的污染源,通过红河入英额河水质断面水质监测数据分析红河水质状况。为全面提升红河流域突发水污染事件应急处置能力,提出了应对和处置工业源、城市生活源及农业面源突发水环境事件的建议。

Accuracy analysis of predicted velocity profiles of laminar duct flow with entropy generation method

The objective of this work is to estimate the accuracy of a predicted velocity profile which can be gained from experimental results, in comparison with the exact ones by the methodology of entropy generation. The analysis is concerned with the entropy generation rate in hydrodynamic, steady, laminar, and incompressible flow for Newtonian fluids in the insulated channels of arbitrary cross section. The entropy generation can be calculated from two local and overall techniques. Adaptation of the results of these techniques depends on the used velocity profile. Results express that in experimental works, whatever the values of local and overall entropy generation rates are close to each other, the results are more accuracy. In order to extent the subject, different geometries have been investigated. Also, the influence studied, and the distribution of volumetric geometries is drawn. of geometry on the entropy generation rate is local entropy generation rate for the selected geometries is drawn.

Collective flow and nuclear stopping in heavy ion collisions in Fermi energy domain

The effects of the in-medium nucleon-nucleon(NN) elastic cross section on the observables in heavy ion collisions in the Fermi energy domain are investigated within the framework of the ultrarelativistic quantum molecular dynamics model. The results simulated using medium correction factors of F=σ_(NN)^(in-medium)/σ_(NN)^(free)=0.2,0.3,0.5,and the density-and momentum-dependent factor obtained from the FU3 FP1 parametrization are compared with the FOPI and INDRA experimental data. It is found that the calculations using the correction factors F=0.2 and 0.5 reproduce the experimental data(i.e.,collective flow and nuclear stopping) at 40 and 150 MeV/nucleon, respectively. Calculations with the FU3 FP1 parametrization can best fit these experimental data. These conclusions can be confirmed in both^(197)Au+^(197)Au and^(129)Xe+^(120)Sn.

R2CROSS方法在南方中小型河道生态流量计算中的适用性和优化讨论

为研究R2CROSS法在南方小型河流生态流量计算中的适用性,分析了R2CROSS方法中湿周率参数的适用条件、典型断面的选择,以及其他水力参数的合理取舍,并提出优化建议。对于R2CROSS方法中的湿周参数,鉴于该方法中对浅滩式河流临界状态的假定前提,在受人类改造影响较大的河道断面中,湿周率参数适宜作为评价因素而非计算因素考虑;对于平均水深和平均流速两个参数,在逐一分析不同水力参数之间的关系的基础上,提出一种参数取值的优化方法:通过推求水深和流速间的量化关系建立了h 23~u曲线,配合同步约束区间,可以较为方便和快速的确定R2CROSS法中平均水深、平均流速参数的合适取值,并从多个断面中选择出适合生态系统水力条件的典型断面。

基于水面一点法的明渠流量计算方法研究

针对当前接触式流速仪测流难度大的问题,提出了一种非接触式流量计算方法。由于渠道水流中垂线平均流速与断面平均流速近似相同,垂线平均流速与垂线水面处流速的比值为恒定值,因此可以通过该恒定值与中垂线水面流速、断面面积三组参数实现对明渠断面流量的计算。以东深供水工程某段矩形明渠为研究对象,对不同垂线上实测流速进行积分计算垂线平均流速,通过实测流速拟合抛物线函数流速分布公式计算垂线水面处流速,同时将垂线平均流速与垂线水面处流速的比值作为流量系数。结果发现,基于该流量系数的计算流量与实测流量十分接近,表明本文提出的水面一点法保证测流精度的同时能有效降低测流难度。提出的基于水面一点法的明渠流量计算方法具有较高精度,可为东深供水工程渠道流量实时监测及其他灌区快速测流提供理论依据。

PEMFC多级横向流道交错流场参数研究

流场结构是质子交换膜燃料电池(PEMFC)的重要组成部分,采用合适的流场结构能显著提高PEMFC的工作效率。设计了一种新型流场结构,将新型流场流道级数以及横截面积作为研究重点,利用三维软件COMSOL Multiphysics对新型流场进行了数值模拟和比较分析。结果表明,随着横向流道级数和进出口面积比的不断增加,电池输出性能均呈现出先增大后减小的变化趋势,采用三级横向流道能使新型流场结构有最高的输出性能,均匀递减型流道可以有效提升电池的输出功率。

阵列变截面球槽结构电解加工流场设计及试验研究

变截面球槽结构表面硬度高、三维形状复杂,采用电解加工具有较好的技术经济优势,但其加工精度和加工稳定性受流场影响比较明显。为提高电解液流场均匀性,基于流场仿真分析探讨了通液方式、流道结构对流场分布的影响规律,并开展了电解加工试验研究。仿真和试验结果表明:采用定向流道供液的分域通液方式有利于提高流场稳定性和流速分布一致性,可以有效提高工艺稳定性;优化出入口流道结构可以进一步提高球槽表面质量,能够满足加工稳定性和加工精度要求。

用于激波增强的变截面激波管设计

相对于常规等截面激波管,相同长度管道条件下,变截面的设计可显著增强入射激波的强度.考察了变截面收缩曲面对激波管内部气体流动特性的影响,进而设计该类新型激波管.基于理想不可压缩一维流动、可压缩流动、经验公式和经验公式加R等4种理论方法,建立了不同的变截面收缩曲面替换段的二维几何模型.以上理论模型结合有限元分析,开展数值模拟研究,获取了亚音速和超音速工况下压力分布等值线云图,进而分析了不同长度收缩曲面的影响.结果表明:相对于其他3类理论方法,基于经验公式加R设计的收缩曲面更适用于变截面激波管的设计.

高速电主轴冷却系统的优化设计

为解决电主轴发热及提升高速电主轴热稳定性的难题,通过研究高速电主轴的基本结构,分析电主轴冷却系统对电主轴的整体温度的影响,探究并联冷却流道、单螺旋冷却流道和双螺旋冷却流道的冷却特性,采用理论计算和有限元仿真相结合对比研究不同流道截面的冷却效果。结果表明,冷却流道截面形状换热效果由好至坏依次为拱桥形、矩形、半圆形和圆形截面,冷却流道截面形状为矩形更符合经济效益。优化后的冷却系统螺旋进水流道尺寸为25 mm×3 mm,出水流道尺寸为15 mm×3 mm时,电主轴的冷却效益最佳。

“释水—断面流”法在矿井涌水量预测中的应用——以鄂尔多斯盆地南缘核桃峪煤矿为例

我国煤炭生产重点逐步西移,西部鄂尔多斯盆地地区既面临水资源短缺问题,又面临严重的矿井水害威胁。在煤矿采掘过程中,能够精准、动态预测矿井涌水量,是预防矿井涌(突)水事故的关键。目前,煤矿最常用的一些矿井涌水量预测方法,如水均衡法、解析法、相关分析法、水文地质比拟法等,因其局限性导致预测误差较大。在前期研究发现,矿井涌水通常由冒裂二元结构体自身释水与其四周外侧边界对称断面释水叠加而成,释水(冒裂含水层自然疏干)持续时间相对较短,随顶板冒裂周期性发生,是间歇性的;边界过水断面汇(渗)水通常是持续的。核桃峪煤矿8号煤开采导水裂隙带直接向上发育能够导通洛河组下段含水层而导致承压水涌入矿井,成为矿井涌水主要威胁。为了精准、动态预测其矿井涌水量,基于前期研究推导的矿井涌水量预测“释水-断面流”公式,充分考虑矿井采掘以及顶板覆岩移动特征,根据顶板岩层冒裂规律对鄂尔多斯盆地南部核桃峪煤矿矿井涌水量进行动态预测。预测结果与实测涌水量相比,其相对误差为11%~23%,较传统解析法的计算精度显著提高。研究成果可为工作面回采过程中不同阶段矿井涌水量的动态预测提供方法基础,为矿井防治水工作开展和合理配备防排水设施提供依据。