随机时延线性系统的IMC-PID设计

基于IMC(内模控制)框架,本文研究了具有随机不确定性时延的FOPDT(一阶时延)对象的最优IAE性能问题及其PID优化设计方法。这是传统的确定性优化方法无法解决的问题。首先,在IMC(内模控制)框架下,借用麦克劳林展开式和一阶泰勒近似,获得了内模控制器及其参数与PID控制器参数之间的关系式。从概率角度出发,通过求解实现IAE性能均值最优化的内模控制器及其参数,并利用上述关系,得到了相应的最优PID控制器参数整定规则,减少了传统参数整定方法的保守性。随机时延参数FOPDT对象的仿真,验证了本文所提出方法的有效性,并且表明:对于随机时延的FOPDT对象,与传统最优IAE PID整定方法如Murrill等(1967)、Smith等(1997)以及Madhuranthakam等(2008)方法相比,本文所整定PID控制器具有更好的IAE性能。福建省自然科学基金资助项目(2012J01288

PID Tuning for FOPDT with Stochastic Parameters

实际的工业过程超过百分之九十的控制回路采用PID控制。PID控制算法是一种理论成熟、应用广泛、通用性强的控制算法。PID控制器的参数整定决定了PID控制系统的性能。合理的PID控制器参数能够提高工业生产效益，因此PID控制器参数整定是工业过程控制的核心问题之一。 针对PID控制器参数整定，国内外学者提出了许多基于控制对象精确模型下的PID控制器参数整定方法。然而，由于被控对象的建模误差、所处环境变化、元器件老化等的原因导致模型及其参数的随机不确定性。因此，在模型具有随机参数条件下，过程控制系统的PID参数整定及其研究具有重要的理论价值和实践意义。绝大多数的实际工业过程控制对象可以由一阶加时延...More than 90% control circuits are still PID control, which is a control algorithm to be mature, widely used and strong currency so far, in practical industrial processes. The tuning parameters of PID controller are crucial to a system’s performance. The reasonable parameters improve the industrial production efficiency, so it is one of the core issues of industrial process control. In view o...学位：工程硕士院系专业：航空航天学院_工程硕士(控制工程)学号：2322013115336

PID Controller Design for Stable FOPDT with Stochasticmulti-parameter

基于IMC(内模控制)框架研究了具有随机时延和时间常数的FOPDT(一阶时延)对象的最优ISE性能问题及其PID优化设计方法。由于传统的确定性优化方法需要确切的先验知识或对系统参数的有效估计,故无法处理上述问题。针对带有双参数不确定的FOPDT对象,本文提出的PID整定方法是在内模控制的框架下,通过非线性最小二乘拟合方法得到ISE性能解析表达式并寻得内模控制器最优参数,从而得到相应最优PID控制器参数。仿真验证了本文的PID参数整定方法的有效性。This paper,on the basis of IMC framework,addresses PID tuning problem for optimal ISE performance of FOPDT with stochastic time delay and time constant. It should be noted that the traditional deterministic tuning methods cannot deal with such problem since they require the exact knowledge or effective estimation of process parameters. The proposed PID tuning method is to get the parametric expression of PID controller and seek the optimal tuning parameter λ through the analytical expression of ISE quality which is obtained by nonlinear least square fitting,so as to obtaining the optimal PID controller. Simulation verifies the effectiveness of the proposed PID tuning method.福建省自然科学基金资助项目(2012J01288

解析粗糙单元的粗糙壁湍流大涡模拟

粗糙壁湍流广泛存在于自然界和工程应用的诸多领域,对其深入研究具有重要的理论价值和现实意义。针对具有复杂粗糙壁面的槽道湍流,本文采用清晰界面浸入边界方法进行了解析粗糙单元的大涡模拟,对模拟结果进行了深入地分析,并将清晰界面浸入边界方法预测的湍流统计量(包括流向速度和雷诺应力等)与文献中采用体积分数法的预测结果进行了对比,发现本研究预测的粗糙度长度高于文献结果。相比于体积分数法,清晰界面浸入边界方法可以更准确地满足粗糙单元上的边界条件。对模拟结果的进一步分析显示这是造成两种方法计算结果差别的主要原因

云南会泽石范铸铁的调查

人为采用范铸工艺已有数千年的历史。以家庭作坊存在的石范铸铁技术此前仅见于云南曲靖市董家村和四川木里县俄亚村。最近在云南会泽县发现了第三处石范铸铁作坊。这家作坊有近百年历史,现仍以四天为一周期铸造犁铧和犁镜,供应当地农户,是迄今所发现规模最大的石范铸铁作坊。从石范刻制、熔炉构造、炉料配比到烘范、浇注等工序都相当成熟,表明这项技术经过长期经验积累达到了较高水平

Wall-resolved large-eddy simulation of turbulent channel flows with rough walls

Turbulent flows over rough surfaces widely exist in nature and industry. Investigating its mechanism is of theoretical and practical significance. In this work we simulate the turbulent channel flow with rough walls using large-eddy simulation with rough elements resolved using the curvilinear immersed boundary method and compare the results obtained in this work with those in the paper by Yuan and Piomelli (J. Fluid Mech., vol. 760, pp. R1, 2014), where the volume of fluid method was employed for modeling rough elements. The mean streamwise velocity profiles predicted by the two methods agree well with each other. Differences in Reynolds stresses and dispersive stresses are observed, which are attributed to the different approaches in dealing with the complex geometry of the rough surface. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics

A structural subgrid-scale model for the collision-related statistics of inertial particles in large-eddy simulations of isotropic turbulent flows

In large-eddy simulations of particle-laden isotropic turbulent flows, the collision of inertial particles is strongly influenced by missing small-scale turbulence. In this paper, we apply the Kinematic Simulation with Approximate Deconvolution (KSAD) model to determine the contribution of small-scale turbulence to the motion of inertial particles and improve the prediction accuracy of the radial distribution function (RDF) and radial relative velocity (RRV), which are closely related to particle collisions. Different values of Stokes numbers (St), which are defined as the ratio of the particle response time to the Kolmogorov time scale, are considered. The KSAD model significantly improves the prediction accuracy of the RRV for all considered St. For the prediction of RDF, good agreement between the KSAD model and direct numerical simulations is only observed for large St, i.e., St >= 2.0. To explore the reason for the poor prediction of the KSAD model for small St, we compare the Eulerian statistics of the flow fields and the Lagrangian properties of the particles from different simulations and find the key reason is that the Gaussian turbulence generated in the kinematic simulation model is inadequate in recovering the vortex centrifugal effect of small-scale turbulence on the inertial particle clustering at small St. Published under license by AIP Publishing

盐间页岩盐离子扩散对自发渗吸驱油的影响——以潜江凹陷潜江组页岩为例

潜江凹陷盐间页岩富含石盐矿物,遇到水后迅速发生盐溶解、扩散,目前对于盐离子扩散对自发渗吸驱油的影响尚不清楚。以潜江凹陷的钙芒硝质盐间页岩、白云质盐间页岩和泥质盐间页岩样品为研究对象,开展页岩油储层逆向自发渗吸实验,采用低场核磁共振测试仪监测盐间页岩的渗吸过程中的油相变化。实验结果显示渗吸水进入盐间页岩后,将孔隙中的油以油滴的形式置换、排驱出来,具有小孔吸水、大孔排油的特征。初期小孔原油排出速率较高,大孔或微裂缝中的原油含量基本不变,但随着小孔原油排出速率的下降,新生的大孔或微裂缝中原油逐渐减少。此外,渗吸过程中,骨架结构中石盐矿物迅速溶解,产生大量的溶孔、裂缝。然而,量纲分析结果表明渗吸速率与石盐矿物含量具有负相关关系,石盐矿物含量越高,渗吸速率越低。石盐矿物的溶解引起颗粒崩落,堵塞基质孔隙,对储层产生了伤害作用,反而不利于孔隙中原油向新生溶孔、裂缝中迁移。研究了盐间页岩油储层中的盐的溶解、扩散机制及其对油动态迁移特征的影响,对盐间页岩的压裂液返排制度的建立和提高页岩油产出具有重要意义

Wall-modeling for large-eddy simulation of flows around an axisymmetric body using the diffuse-interface immersed boundary method

A novel method is proposed to combine the wall-modeled large-eddy simulation (LES) with the diffuse-interface direct-forcing immersed boundary (IB) method. The new developments in this method include: (i) the momentum equation is integrated along the wall-normal direction to link the tangential component of the effective body force for the IB method to the wall shear stress predicted by the wall model; (ii) a set of Lagrangian points near the wall are introduced to compute the normal component of the effective body force for the IB method by reconstructing the normal component of the velocity. This novel method will be a classical direct-forcing IB method if the grid is fine enough to resolve the flow near the wall. The method is used to simulate the flows around the DARPA SUBOFF model. The results obtained are well comparable to the measured experimental data and wall-resolved LES results