注塑成型Hele-Shaw流动模拟中热对流的异步长求解

在Hele-Shaw流动数值模拟中,速度是压力的后处理结果。如果是点浇口,则浇口附近速度会随单元尺寸缩小而趋于无穷大,导致能量方程作为一个整体求解时,时间步长必须非常小,否则会产生很大误差;而根据热对流物理意义分步求解,则需追踪当前物质在上一时刻位置,当单元速度很高、逆向搜索需穿透多个单元时,搜索可能会失败。鉴于此,基于分步求解法,研究提出一种变长度子时间步长方法处理对流项,确保搜索路径局限在当前单元内,并采用二分法确定子时间步数量,使算法简洁有效。算例表明,该方法在保证计算精度和求解稳定性的同时,可以明显减少计算时间,提高计算效率。     

双曲线输入约束下一类基于斐波那契序列的变步长预测控制算法

定步长预测控制在处理双曲线型输入约束时不能保证存在可行解。变步长可以保证得到可行解,但难点是步长值的确定。提出应用斐波那契序列搜索步长的算法,避免了步长搜索引入的在线求解子优化问题的复杂性,并且给出了算法的稳定性证明。     

注射成型中聚合物熔体充填流动的数值模拟

在建立聚合物熔体充填三维流道—浇口—型腔系统的数学模型的基础上,采用混合有限元/有限差分方法求解,并对入口结点的压力计算以及熔体前沿推进时时间步长的确定准则作了修改。编制程序实现提出的算法,给出两个算例说明数值模拟的结果。     

注塑流动与传热分析的自适应隐式控制体积法

在注塑流动与传热分析中采用自适应隐式控制体积法,利用自动控制的参数识别方法来自动调节时间步长,在每个时间步长流动将向前推进大约半个单元大小的距离,厚度方向的温度采用契比雪夫配点法进行计算,压力方程的求解方法是预条件共轭梯度法。计算结果表明,自适应隐式控制体积法的时间复杂度是结点数目的平方,而且1h之内可以求解10000结点规模的问题。     

砂岩酸化模型数值计算误差研究

酸化是砂岩油藏提高采收率的重要方法,前期需要通过数值模拟确定酸化方案,以保障酸化工程达到预期效果,但酸化模型数值求解过程中的误差影响着最终结果的准确性。本文从砂岩酸化的化学原理出发,建立了砂岩酸化的数学模型,在此基础上研究了数值求解中,不同时间步长和空间步长组合下误差对模型求解结果的影响。研究发现,不同求解步长组合对模型的求解结果具有较大的影响,当步长设置不合理时,求解过程中的误差会使最终结果出现严重偏差,且求解对空间步长更为敏感。研究对于指导砂岩酸化工程的准确实施具有重要意义。     

注射模塑中的冷却时间和浇口封闭时间的计算

本文用两种方法来计算冷却时间,一种是从理论分析中经过合理的假设,推导出冷却时间和浇口封闭时间;另一种是作图法求解冷却时间。     

自适应时间步长在化学驱油藏模拟中的应用

目前国内大多化学驱数值模拟软件中应用了固定时间步长或者通过组分浓度控制时间步长的方法,在油藏模拟计算过程中,算法的稳定性受限于时间步长的设置及模型对其他参数的敏感性。通过在软件中加入压力-组分浓度联控时间步长,以及在方程不收敛时自动修正当前时间步长重新计算的功能,改进了化学驱数值模拟软件的计算稳定性,并通过概念模型和矿场模型的应用对改进的功能进行了验证。     

基于分步法的三维注塑充填温度场数值模拟

注塑成型的充填过程是一个对流占优的能量传递过程。在采用经典Galerkin有限元法求解该瞬态温度场时,对于固定的计算网格,如果时间步长选择的不合理,容易造成其稳定性要求得不到满足,从而导致方程的求解失败。鉴于此,本文采用分步法将该能量守恒方程分解为一个对流方程和一个热传导方程,针对这两个方程的不同特点,分别选择不同的时间步长和求解方案独立进行求解,解决了由于对流项而引起的方程求解失稳问题。另外,针对瞬态热传导方程的求解,分析了利用向后差分法离散其瞬态项时,采用协调质量热容矩阵容易产生不合理计算结果的原因,进而用集中质量热容矩阵代替协调质量热容矩阵对该方程进行求解,得到了合理的模拟结果。最后采用具体的数值算例验证了该模拟方案的正确性。     

基于神经网络控制的共轭梯度法

共轭梯度法中搜索步长是通过某种搜索策略得到,许多情况下的收敛速度较慢。为了加快其收敛速度,提出了通过引入具有“先验知识”的神经网络对共轭梯度算法中的搜索步长进行控制。实验结果表明,该模型实现的共轭梯度法对于加快收敛速度有效。     

塑料注射充模流动分析的自适应隐式方法

提出了一个注射充模数值模拟隐式方法的时间步长选用标准,依据“一时间步,一单元层”的思想,采用最小二乘递推法估算每一步的时间步长,并依据压力估算每个控制体积的半注满时间,从而可以重构任何时间的流动前锋。计算表明本方法极大地提高了隐式方法的适用性,并把注射充模流动数值模拟的计算时间复杂度降到结点数的平方。     

Optimization‐Based Nonlinear Centralized Controller Tuning of Liquid‐Liquid Extraction Processes

Abstract

The control problem of an agitated contactor is considered in this work. A Scheibel extraction column is modeled using the non‐equilibrium backflow mixing cell model. Model dynamic analysis shows that this process is highly nonlinear, thus the control problem solution of such a system needs to tackle the process nonlinearity efficiently. The control problem of this process is solved by developing a multivariable nonlinear control system implemented in MATLAB?. In this control methodology, a new controller tuning method is adopted, in which the time‐domain control parameter‐tuning problem is solved as a constrained optimization problem. A MIMO (multi‐input multi‐output) PI controller structure is used in this strategy. The centralized controller uses a 2×2 transfer function and accounts for loops interaction. The controller parameters are tuned using an optimization‐based algorithm with constraints imposed on the process variables reference trajectories. Incremental tuning procedure is performed until the extractor output variables transient response satisfies a preset uncertainty which bounds around the reference trajectory. A decentralized model‐based IMC (internal model control) control strategy is compared with the newly developed centralized MIMO PI control one. Stability and robustness tests are applied to the two algorithms. The performance of the MIMO PI controller is found to be superior to that of the conventional IMC controller in terms of stability, robustness, loops interaction handling, and step‐change tracking characteristics.     

A novel predictive homotopic path tracking algorithm to solve non-linear algebraic equations

In chemical engineering and other areas of mathematics and engineering sciences, systems of non-linear algebraic equations often must be solved, and a problem is that these types of systems often cannot be solved analytically. Homotopic continuation methods are globally convergent and can find several solutions to the analyzed algebraic system and consist of a predictive step followed by a corrective step, which can cause reversion of homotopic path tracking. Therefore, in this work, the use of a homotopy continuation method (HCM) based on a purely predictive methodology is proposed; that is, it only makes use of predictor vectors (without correction vectors) to find the solution to several systems of non-linear algebraic equations with a multiplicity of solutions, employing lower central proccessing unit (CPU) time in comparison with standard homotopic tracking algorithms.     

The ascend-II system—a flowsheeting application of a successive quadratic programming methodology

This paper describes ASCEND-II, an interactive equation based flowsheeting system capable of doing performance, design and optimization calculations with comparable ease. The optimization capability is a new, as yet unpublished, successive quadratic programming method operating in the reduced space which is the size of the degrees of freedom for the problem. Its performance is very encouraging.We spend considerable time describing the ASCEND-II system details because we believe the concepts underlying it make the system a powerful aid for design. It allows one to evolve toward the solution to a problem by allowing one to add and delete model complexity, interactively alter which variables are to be calculated and which fixed, single step through the convergence of a model, move easily from design to optimization and back, use any variable as an objective to be maximized or minimized, and to place an upper or lower bound on any variable desired.     

Unsteady mass transfer around axisymmetric drops of revolution in variable diffusion coefficient liquids

Unsteady mass transfer in the continuous phase around axisymmetric drops of revolution at high Peclet numbers has been theoretically studied. The liquid is a binary system, having a variable diffusion coefficient, which depends on the solute concentration. The solution to the problem was obtained by extending the theory of Favelukis and Mudunuri, developed for a constant diffusion coefficient liquid. The procedure consists of transforming the differential mass balance, for a binary system, into a partial differential equation which has an analytical solution, and an ordinary differential equation that needs to be solved numerically. Solutions to a large number of problems can be immediately obtained with the only requirements being the shape of the drop, the tangential velocity at the surface of the drop and an expression for the variable diffusion coefficient liquid. An approximate analytical solution is also suggested which is in excellent agreement with the numerical results.     

单颗粒褐煤高温烟气干燥过程数值模拟

褐煤干燥对于提高其品质具有重要意义。为了模拟高温烟气干燥这一高温差、变温差非稳态传热传质过程中褐煤内水分蒸发过程,采用有限体积法建立了一维球坐标系下蒸发界面向内迁移的单颗粒褐煤干燥数学模型,并利用该模型分析了初始烟气温度和颗粒粒径对单个褐煤颗粒干燥特性的影响。模型模拟结果与实验结果对比表明二者变化趋势一致,所建模型能较好地反映出高温烟气干燥过程中褐煤内水分蒸发过程。结果表明,初始烟气温度越高,颗粒粒径越小,蒸发界面向内迁移速度越快,水分脱除越快,干燥时间越短;蒸发界面平均迁移速度均与初始烟气温度和颗粒粒径呈线性关系;在初始烟气温度700℃下,较短的停留时间使得颗粒表面温度未达到挥发分析出温度,本研究中不同粒径褐煤颗粒在干燥过程中基本没有挥发分的析出。     

注塑成型充填过程数值模拟的隐式算法

应用有限元 /控制体积方法 ,基于熔体在控制体积内的质量守恒 ,以结点压力和充填分数为未知量 ,建立了熔体在充填阶段流动的控制方程 ,并对方程进行隐式求解 ,完成了对注塑成型充填过程的数值模拟 .算例分析证明算法是正确的     

数据流模块化电测井技术研究

随着计算机技术的发展,大数据逐渐在我们工业领域应用范围越来越广,其中石油行业对大数据的应用就越来越重视。模块化技术就是一种很有用的技术手段,他可以简化问题的研究方法,一个复杂的问题或者说思路,我们可以将其分开,分成互相独立,有互有联系的几部分,这几部分之间可以用某种方法联系起来,为一个部分都可以独立研究,解决好每个部分的问题,在将之联系起来,这个复杂的问题也就得到了解决,并且,由于每个部分之间是互相独立的,所以他们可以同时进行,不用想一般的问题一样,必须按顺序逐步解决,不仅解决了人力的浪费问题,还节省了时间。两者结合起来,数据流模块化技术在测井方面应用会带来巨大的效益,也可以促进国内对此方面的研究。     

Fast continuous‐discrete DAF‐filters

This article introduces a new method for nonlinear continuous‐discrete filtering. It is shown that the Fokker–Planck‐equation can be solved numerically by using distributed approximating functionals (DAFs). The approximation is very accurate and resolves the time interval between observations in one calculation step. Additionally, the operator matrix has to be evaluated only once and not necessarily online. Therefore, the method is very efficient.     

基于解耦控制的焦炉集气管压力控制系统

针对焦炉集气管压力系统具有多回路、强耦合、非线性的特点 ,提出了一种运用相关性分析法的解耦控制算法 ,并将该算法与变积分PI控制有机结合 ,解决了具有相互耦合的多座焦炉的集气管压力稳定问题。实际运行结果表明该方法简单实用 ,可靠有效。     

Numerical simulation of resin transfer molding using linear boundary element method

Using mass conservation and Darcy's law to describe flow through isotropic porous media leads to a Laplace equation, which may be solved numerically at each time step using the boundary element method. For anisotropic porous media in which the permeability matrix is symmetric, the problem can be solved in the same way by rotating and stretching the coordinates. The numerical model has been compared with analytical solutions and experimental data in the case of radial front flows and with finite element for a frontal injection.