Modeling and simulation of an industrial‐scale parex process

The Parex unit for industrial‐scale purification of p‐xylene was studied through detailed simulation and the accuracy of the developed model tested against real industrial data. Starting from a comprehensive analysis of the construction and operation of the industrial unit, a simulation model was developed that incorporates the existing three major types of dead volumes: bed lines, which connect the beds to the rotary valve, circulation lines, which connect adjacent adsorbent chambers, and bed‐head dead volumes, which are located upstream of each bed due to the existence of internals. By gathering operation data and surveys in the pumparound line and in the extract stream, three case studies were defined and compared with simulation results. The model is capable of predicting the performance of the industrial unit. Further simulations were made and compared with plant data to assess the effect of adsorbent capacity loss on the long‐term performance of the unit. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1345–1363, 2015     

Apparent Molar Volumes of N,N – Disubstituted Monoamides: A Convenient Tool to Interpret Iron(Iii) Extraction Profiles from Hydrochloric Acid Solutions

New iron(III) extraction data involving two N,N-disubstituted monoamides, N-ethyl-N-phenyloctanamide (EPHOA) and N-ethyl-N-cyclohexyloctanamide (ECHOA), from hydrochloric acid media, are presented and discussed. These, and earlier results obtained with other similar N,N-disubstituted monoamides, are interpreted in this work through their apparent molar volumes in 1,2-dichloroethane, and all the information is being used to screen for solute-solute and solute-diluent interactions. The results collected help to understand why N-cyclohexyl monoamides are generally more efficient than their N-phenyl analogues as liquid-liquid extractants for iron(III) from 3 to 5 M hydrochloric acid solutions, and clearly denote that N-phenyl monoamides are essentially monomeric whereas N-cyclohexyl monoamide derivatives have a tendency to aggregate in the organic solution.     

Polystyrene sphere monolayer assisted electrochemical deposition of ZnO nanorods with controlable surface density

In this paper we report the zinc oxide nanorods (ZnO NRs) growth by electrochemical deposition onto polycrystalline gold electrodes modified with assemblies of polystyrene sphere monolayers (PSSMs). Growth occurs through the interstitial spaces between the hexagonally close packed spheres. ZnO NRs nucleate in the region where three adjacent spheres leave a space, being able to grow and projected over the PSSMs. The nanorod surface density (N_NR) shows a linear dependence with respect to a PS sphere diameter selected. XRD analysis shows these ZnO NRs are highly oriented along the (0 0 2) plane (c-axis). This open the possibility to have electronic devices with mechanically supported nanometric materials.     

Third-order accurate finite volume schemes for Euler computations on curvilinear meshes

After looking for a convenient definition of accuracy for finite-volume schemes on structured meshes, a high-order accurate scheme is constructed for the Euler equations. Thanks to suitably weighted discretization operators, the proposed scheme is third-order on mildly deformed grids and second-order on highly deformed grids. The influence of mesh deformations on the scheme accuracy is studied theoretically and numerically. Numerical results are shown for a Lamb vortex, subsonic flow past a cylinder and transonic flow past a NACA0012 airfoil.     

利用弹簧质点模型和隐式方法的布料模拟研究

首先运用弹簧-质点模型建立布料的面模型,然后对质点进行力的分解以及受力分析并优化。提出逼近的隐式数值积分方法模拟质点的运动轨迹,这解决了显式数值积分方法的不稳定性和小时间间隔的缺点和其他隐式方法计算量大的缺点,这也是实现基于物理模型的布料仿真的关键技术。针对具体碰撞对象采用简单的包围盒方法进行碰撞检测,和利用二分法进行碰撞的处理,大大增加了碰撞处理的逼真效果。实验证明其模拟方法具有稳定性和实用性。     

利用动态多分辨率LOD技术的地形简化研究

使用三角形二叉树数据结构,对地形进行合适的分块处理,使得每次只处理局部的地形;提出包围球与包围圆锥混合的方法对地形进行合理的裁剪,并依据视点变化和对应的顶点误差生成自适应地形层次细节。减少了大量的冗余操作,避免了裂缝的出现和细节转换时地形的跳跃问题,减少了数据处理量并降低了计算复杂度。     

一种基于分块思想的多纸张缺陷一次提取算法

为了解决纸张缺陷检测中多个纸病区域的提取实时性问题,提出了一种采用“先分块、后合并”思想直接对实时图像数据流进行处理的并行化纸病提取算法。该算法充分利用现场可编程门阵列（FPGA）的并行处理特性,在跨时钟域对图像数据进行传输的同时,在另一个分支流程中并行地对分块缺陷连通域进行标记以获取每个缺陷的相对位置坐标,最后以包围盒的形式提取出纸张缺陷区域。该算法基于分块思想,分支处理过程不需要消耗主流程额外的处理时间且硬件资源占用率极小。实验结果表明,该算法能够准确、快速地提取出各种常见纸张缺陷,具有很强的灵活性和实时性,能够满足在线纸病检测的实时性要求。     

考虑时间效应边界面模型在地铁工程中的应用

 为了真实刻画地铁移动荷载低振幅、高振次特征,准确计算软土地铁地基在运营期的长期沉降,需要提出能描述低应力水平下土体动蠕变特性的本构模型。据此,基于边界面本构模型,结合Mesri蠕变模型,建立考虑时间效应的边界面本构模型。随后,为了开发ABAQUS材料子程序,采用应力积分算法对本构模型进行推导,借鉴阻止应变法进行算法的优化,可以使计算间隔缩短,总迭代次数增多,更易收敛。采用提出的本构模型和南京软土GDS动三轴试验获得的相关参数进行数值模拟计算,并进行试验对比,验证本构模型的有效性。同时,将开发的本构模型嵌入数值模拟计算中,设置黏弹性人工边界,进行三维地铁有限元数值模拟分析。结果表明：(1) 基于阻止应变法的优化算法可以进行推广使用;(2) 考虑时间效应的边界面本构模型适合描述软土动蠕变特性,能有效预测软土在低振幅地铁移动荷载作用下的累积沉降。研究对理论研究和实际工程具有重要的指导意义。     

适用于膨胀性非饱和土的边界面模型的数值实现

基于完全隐式的Euler向后积分算法,对一个适用于膨胀性非饱和土的边界面模型提出一种应力积分方法。模型中的塑性变形具有双重机制即加载–湿陷机制和微观结构机制,并考虑力学行为与持水滞回间的耦合作用。依据当前应力状态、力学与持水模型中各塑性机制的发生情况,将应力积分过程中的当前增量步分为多种情况,针对每一情况利用Euler向后算法进行试算,并依据判定准则选取结果。其次,利用该模型分别对已有的吸力循环试验和三轴压缩试验进行了验证,以此反映模型的预测能力和算法的运行能力。最后,对比不同步长的应变控制试验路径下的计算结果,以此验证应力积分方法的稳定性和精度。     

一种快速计算参数曲面间Hausdorff距离近似值的方法

针对曲面间Hausdorff距离计算复杂度高、相关计算方法少的问题,提出一种三角面片-包围盒方法快速计算参数曲面间Hausdorff距离的近似值。曲面离散化后的三角面片集合可以较好地逼近曲面,借助这一特性,将曲面间的Hausdorff距离近似转化为三角面片集合间的Hausdorff距离。在具体计算过程中,辅之以包围盒技术对无效的三角面片进行排除,以提高计算效率。为进一步简化两三角面片间的距离计算,在误差可控范围内提出采样点近似计算方法。实验表明,与曲面直接构造包围盒方法相比,该方法简便、易于实现、排除率高,在不影响计算结果的情况下,计算效率显著提高,有广泛的应用价值。