Modeling and experimental studies of methyl methacrylate polymerization in a tubular reactor

In this study, rheological examination of the mixture of a tubular reactor in which methyl methacrylate was polymerized has been studied. The n(flow behavior index) value of Power Law Model of mixture contained in the reactor has been determined within the span of 0.3492 to 0.9889 by curve fitting. Employing these numerical data for velocity profile, the reactor has been modeled. Moreover, the functions of the reactor have been compared in the three modes of plug, mixed and laminar flow. The results obtained in this research indicate that the polymethyl methacrylate mixture contained in the reactor is pseudo-plastic. Moreover, as the conversion grows, the velocity profile starts as a parabolic profile and approaches the plug mode; although it never reaches the plug. The other conclusions borne in this study indicate that when the reactor's radius is decreased, the conversion rate grows. However, as decreasing the radius would also reduce the productions rate, this procedure is not economical. Finally, in this modeling, the amount of conversion is equal to 56.47% at the end and according to its laboratory proportion which is 55.88%, it has reached the conclusion that the modeling duly undertaken is applicable and valid.

A Ring Model for Limit Analysis of Spatial XX Tubular Joints

-A ring model is developed to investigate the ultimate strength of tubular X and XX joints in the case that the brace is compressed. In the present analysis, the tubular joint is made of elasto-perfectly-plastic material, and the arch element of the chord section intersecting with the brace is assumed to be rigid. It is found that when 6 plastic hinges for X joint and 8 plastic hinges Tor XX joint appear in the ring, the limit state is reached, and by means of the equivalent ring width Be formula proposed in a previous paper by the authors, the ultimate strength of tubular X and XX joints subjected to compression can be obtained.

Coupled simulation of recirculation zonal firebox model and detailed kinetic reactor model in an industrial ethylene cracking furnace

A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convection to simulate heat transfer in the furnace.A two-dimensional recirculation model is proposed to estimate the flow field in furnace.The reactor model integrates the feedstock reconstruction model,an auto-generator of detail kinetic schemes,and the reactor simulation model to simulate the reaction process in the tubular coil.The coupled simulation result is compared with industrial process and shows agreement within short computation time.

Symmetrical adhesion of two cylindrical colloids to a tubular membrane

With the full treatment of the Helfrich model we theoretically study the symmetrical adhesion of two cylindrical colloids to a tubular membrane. The adhesion of the rigid cylinders with different radius from the membrane tube surface can produce both shallow wrapping with relatively small wrapping angle and deep wrapping with big wrapping angle. These significant structural behaviors can be obtained by analyzing the system energy. A second order adhesion transition from the desorbed to weakly adhered states is found, and a first order phase transition where the cylindrical colloids undergo an abrupt transition from weakly adhered to strongly adhered states can be obtained as well.

Prediction of Static Strength of Tubular T and X Joints Subjected to Axial Compression

-The formulation of ring analogy method for the prediction of static strength (ductile collapse) of tubular T, X joints under axial compression based on the limit analysis of the ring with some assumptions is presented in this papaer. The regression formula for the effective length of the chord based on test results is established by means of the least square method. The results computed by the present semi-analytic formula are compared with previous results and test data. They are quite close to each other. The accuracy of the present formula depends on the reasonable selection of the effective length of the chord, which requires numerous test data.

KT形钢管相贯节点受力性能试验研究

依托某户外剧场钢结构顶棚结构设计,首先对其管桁架关键KT形钢管相贯节点进行了足尺模型试验,测试分析了该节点相贯线、主管及支管应变分布规律。试验结果显示,在最大荷载作用下,相贯节点因支管相贯线附近部分屈服而不能继续承载,其余位置未屈服,表明支管相贯线附近位置是该相贯节点最薄弱位置。然后运用ANSYS有限元软件建立KT形钢管相贯节点有限元模型,将试验结果与有限元分析结果作对比,验证了有限元模型的准确性。最后通过有限元模拟探讨了增大支管厚度以及增设加劲肋对节点受力性能的影响。有限元分析结果显示,增大支管厚度对其受力性能影响较小;增设加劲肋可以有效降低支管相贯线附近位置的最大应力水平,能有效延缓支管屈服,明显提高管桁架节点的承载力。

Development and Application of a Shaft-type Tubular Pumping System with a Siphon Discharge Passage

Based on the characteristics of large flow rate , low head , short annual operation time , and high reliability of the city flood-control pumping stations , a new-type shaft tubular pumping system featuring a shaft suction box and a siphon-type discharge passage with a vacuum breaker as the cutoff device was developed , which possesses such advantages as simple structure , reliable cutoff , and high energy performance.Taking some pumping stations as the case studies , in the light of the specified operation conditions , the hydraulic optimal design of the shaft-type tubular pumping system was determined and the optimized shape of the system was recommended.The performance prediction based on the computational fluid dynamics methodology was determined and the model test verification was conducted.The results show that the predicted data agree with the experimental head and efficiency so that both methods can be used to determine the performance of a real pumping station.Finally , the in-situ measurements of a pumping station during the commissioning period further verified that the shaft-type tubular pumping station with a siphon discharge passage is of higher efficiency , more reliable and stable.

管型航路与终端管制区衔接运行方法研究

随着航空运输业高速发展,航路运行容量日趋饱和,为解决容量与流量不均衡情况,众多研究机构提出面向下一代的空中交通管理概念,其中管型航路新型空域概念应运而生。基于未来新型管型航路运行概念和模型,结合传统航路与终端区衔接方法相关研究,建立衔接模型的物理结构,提出航空器在管型航路及融合程序中的运行模式,构建管型航路仿真平台进行性能分析,综合利用概率论、统计学等理论,研究不同衔接方法对交通流的影响机理及运行效率。研究表明,所设计的管型航路-终端管制区衔接模型,可承载大流量时的运行负荷,提升航路平均容量与航班运行效率,降低航空器的冲突率和日延误时间,同时兼顾航路容量和安全风险。

轴压下FRP管-混凝土-钢管组合柱可靠性分析

以85个FRP管-混凝土-钢管双壁空心柱(double-skin tubular column,DSTC)轴压试验数据作为统计样本,评估了几种现有FRP约束混凝土强度模型,最终选择Teng模型进行可靠性分析,并确定了强度模型误差和构件抗力的最佳概率分布.运用JC法对DSTC进行可靠度计算.结果表明:可靠指标随着钢管强度、中空率和含钢率的提高而升高,而对混凝土强度的变化不敏感.FRP约束应力的增加会导致可靠指标的下降.基于可靠指标目标3.7,提出一个适用于DSTC的抗力分项系数表达式.

基于粒子群优化BP神经网络的中空夹层钢管混凝土柱轴压承载力研究

圆中空夹层钢管混凝土(concrete filled double-skin steel tube,CFDST)柱因其独特的结构形式与优异的力学性能,已成为现代工程结构中的主要受力构件。然而外钢管、内钢管与核心混凝土之间的相互约束作用导致其受力比较复杂。为此,采用PSO-BP混合神经网络算法对圆CFDST柱的轴压承载力进行了研究。收集了167组数据建立数据库,并选取8种影响因素作为输入层参数,轴压承载力作为输出层参数,分析了传统BP神经网络模型所存在的缺陷,建立了PSO-BP神经网络模型。此外,将机器学习模型与3种规范的结果进行比较,结果表明机器学习模型的精度比3种规范的精度更高。相较于BP神经网络模型,PSO-BP神经网络模型具有更好的预测能力,更有助于预测CFDST柱的轴压承载力,对工程上研究CFDST柱的力学性能有着重要意义。

管式PECVD设备腔内大容量石墨舟力学性能的数值分析

提高等离子体增强化学气相沉积(PECVD)法制备的氮化硅薄膜品质在太阳电池光电转换效率领域有举足轻重的作用。承载大量硅片的石墨舟是管式PECVD设备中的关键核心部件,随着生产效率的不断提升,热力耦合环境下腔内大容量石墨舟力学性能的稳定性引人关注。通过CAD软件建立石墨舟有限元模型并使用ANSYS仿真软件进行热力学仿真研究,综合分析其在高温条件下受力、受热后的变形情况。研究结果显示:结构自重是石墨舟形变及应力集中产生的主要因素,温度产生的影响并不明显;采用结构增强设计可有效提升石墨舟整体的力学性能。

新川沙泵闸大型双向泵装置调速性能及试验

对于引水和排涝扬程相差较大的低扬程大型双向泵站,需兼顾双向运行工况下的水泵装置性能,有必要对该类泵站水泵装置性能及运行方式适配性进行研究。以目前国内引水规模最大的双向竖井贯流泵站新川沙泵闸为研究对象,进行水泵机组设计及性能调节研究。泵站引、排设计净扬程分别为0.68、2.79m,比较分析了不同调节方式下的水泵性能改善效果。通过CFD数值计算和装置模型试验验证了设计的合理性,并对不同转速下水泵的性能进行了测试。研究结果表明,在性能调节方面,变频变速调节效果优于叶片调节,对各种工况运行适用性更强;降速运行时,水泵装置整体效率略有下降,但降至0.8倍额定转速范围内,高效区效率仅下降1%左右。根据水泵性能测试结果,提出了不同扬程范围变速运行调节控制方案,可为今后大型双向泵站选型及运行调节方式提供借鉴。

双向潜水贯流泵装置性能试验与数值分析

该文针对城市防洪排涝泵站的特点,研发了2套双向潜水贯流泵装置,并采用CFD(computational fluid dynamics)技术计算了双向潜水贯流泵装置的内流场,分析了灯泡体段对泵装置正反向运行的影响,包括灯泡体段的水力损失、导叶体内部的流态及"S"形叶轮的水力性能,并经试验验证分析了数值计算结果的有效性。计算结果表明,反向运行时导叶体内部流态较好,反向运行工况优于正向运行;正向运行工况流量为4和5m3/s时,导叶体内均出现涡旋;灯泡体支撑件对"S"形叶轮的水力性能影响极小,但对泵装置水力性能影响较大;正向工况时"S"形叶轮所受轴向力小于反向工况。通过泵装置模型性能试验比较了2套泵装置的综合水力特性指标,并给出了供参考的潜水贯流泵装置的结构尺寸,其中导叶体扩散角为3°,灯泡体长度为2.43D、灯泡体直径为0.46D、泵装置总长为13.45D(D为叶轮名义直径),灯泡体采用流线型尾部及5片支撑件。

槽式太阳能真空集热管的热损失研究

建立了真空集热管中吸收管与玻璃管之间热辐射和残余气体热对流、玻璃管与外界环境之间热对流和玻璃管对天空热辐射的数学模型,提出了模型的计算方法,并通过和实验数据的比较验证了模型的准确性。同时利用模型分析了几种影响热损失的主要因素,分析结果表明:吸收管温度越高,热损失越大;环境温度越低,风速越大,热损失越大,但影响很小;选择性吸收涂层的发射率是影响热损失的主要因素;真空度对热损失也有很大影响。

手太阴肺经在虚拟人体上的可视化研究

目的:显示手太阴肺经在虚拟人上的体表循行路线。方法:通过定义腧穴为控制点,并适当插值,合成骨架曲线,实现面绘制,重建经脉管状模型。结果:重建后的经脉模型视觉效果好,并可以显示手太阴肺经循行路线上不同层次的解剖结构。结论:初步实现了手太阴肺经在虚拟人体上的可视化显示,为构筑经络研究平台提供了数据载体。

复合材料圆管构件的等效模型研究

本文针对任意壁厚的复合材料圆管构件的等效弹性模量和剪切模量提出了高阶理论计算方法，它考虑了构件的横向剪切效应以及层合材料的三维本相关系，并且对三种缠绕方式的等效模量进行了预测，预测结果与经典层合报理论和实验的预测结果吻合较好，该方法可用于复合材料杆件结构的设计中。

任督二脉在数字人体上的可视化研究

目的:显示任督二脉在数字人体上的体表循行路线,为经络教学和科研提供平台。方法:通过定义腧穴为控制点,并适当插值,合成骨架曲线,实现面绘制,重建经络管状模型。结果:重建后的经络模型视觉效果好,并可以显示任督二脉的体表循行路线及其腧穴和不同层次的解剖结构。结论:任督二脉在虚拟人体上的可视化显示可为构筑经络教学和研究平台提供数据载体。

管状喷射沉积坯成形过程数值模拟

喷射成形是一种近终形材料加工技术,针对管状沉积坯的成形过程进行了模拟。首先建立了管状沉积坯成形过程的数学模型,然后模拟了沉积坯厚度变化过程。结果表明:沉积器平移速度、沉积器半径、喷射距离对沉积层厚度均产生影响;而沉积器旋转速度超过30r/min时,该参数对沉积层厚度影响可以忽略。

灯泡贯流泵流道模型水力损失的测试

为了配合某大型泵站贯流泵装置的优化水力设计研究工作,本文提出了设计专用模型试验装置,将贯流泵装置进水流道和出水流道从水泵装置模型中分离出来分别进行模型试验及水力损失测试的方法。介绍了新方法所采用的测试装置及测试设备、试验准则、水力损失计算方法等有关问题。采用本文的方法对某泵站前置灯泡和后置灯泡贯流泵的进、出水流道分别进行了模型试验,测试了流道水力损失。试验结果表明:采用新方法进行贯流泵进出水流道水力损失的测试,可以较为方便地得到准确的结果;贯流泵装置进、出水流道的水力损失与灯泡布置的位置密切有关。

深水导管喷射安装过程中管柱力学分析

根据深水导管喷射安装作业特点,建立了该过程中的管柱静力学模型,并应用加权残值法进行了求解,得出了在考虑环境载荷、钻柱结构及钻井船偏移等因素影响下的管柱变形和应力分布规律。研究结果表明,中深层海流对管柱变形影响最大,合理设计钻柱结构和控制钻井船偏移是保证深水导管垂直安装和钻柱抗拉强度安全的关键。深水管柱的弯曲正应力在钻柱的上下两端作用明显,进行钻柱强度设计时,必须考虑管柱横向变形引起的弯曲正应力,提出了相适应的钻柱结构优化方案。作业初期,钻井船向海流负方向适当偏移,有利于控制导管的入泥倾角;遇阻活动管串时,钻井船向海流正方向适当偏移,能够有效地降低钻柱危险截面上的最大拉应力。