Multivariable real‐time optimal control of a cooling and antisolvent semibatch crystallization process

This article presents an experimental study of simultaneous optimization with respect to two variables (cooling rate and flow‐rate of antisolvent) in an offline and online (real‐time) manner on a semibatch crystallizer. The nucleation and growth kinetic parameters of paracetamol in an isopropanol‐water cooling, antisolvent batch crystallizer were estimated by nonlinear regression in terms of the moments of the crystal population density. Moments of crystal population were estimated from the measured chord length distribution, generated by the FBRM®, and the supersaturation was calculated from the measured concentration by attenuated total reflectance‐fourier transform infrared spectroscopy. The results of real‐time optimization showed a substantial improvement of the end of batch properties (the volume‐weighted mean size and yield). For the same objective function, the real‐time optimization method resulted in an increase in the volume‐weighted mean size by ～100 μm and 15% of theoretical yield compared with the best result obtained in an offline optimization manner. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

A robust pole-placement self-tuning controller for chemical process control: Theoretical studies and simulation

A single variable pole-placement self-tuning controller (PPSTC) is used to simulate examples typical of chemical processes; i.e., open-loop stable, unstable, and unstable non-minimum phase systems with unknown varying process dead time. The PPSTC is shown to be effective in each case. Set-point tracking and rejection of randomly occurring deterministic disturbances for all three types of processes are achieved. Simultaneous estimation of process parameters and process time delay is realized by using a recursive extended least squares method.     

Directionally sensitive MCUSUM mean charts

In the context of a disease outbreak detection, a prime interest is to only detect increases in the process mean. It is thus desirable to have a directionally sensitive multivariate chart that can effectively detect either increases or decreases in the process mean vector. In this paper, with a suitable transformation that truncates multivariate observations either above or below the process mean vector, we propose one-sided and two one-sided MCUSUM charts for monitoring the mean of a multivariate normal process. Among the proposed charts, the one-sided MCUSUM charts are directionally sensitive, while the two one-sided MCUSUM charts are directionally insensitive. In addition, the fast initial response feature is also incorporated into the proposed charts to enhance their sensitivities against initial process shifts. The run length characteristics of these control charts are computed with the Monte Carlo simulation. Based on the run length comparisons, it is found that the proposed charts are more sensitive than the existing charts when detecting moderate-to-large shifts in the process mean. The proposed charts are also applied on real datasets to support the theory.     

Solving a class of nonlinear optimal control problems via he’s variational iteration method

This paper presents an analytical approximate solution for a class of nonlinear quadratic optimal control problems. The proposed method consists of a Variational Iteration Method (VIM) together with a shooting method like procedure, for solving the extreme conditions obtained from the Pontryagin’s Maximum Principle (PMP). This method is applicable for a large class of nonlinear quadratic optimal control problems. In order to use the proposed method, a control design algorithm with low computational complexity is presented. Through the finite iterations of algorithm, a suboptimal control law is obtained for the nonlinear optimal control problem. Two illustrative examples are given to demonstrate the simplicity and efficiency of the proposed method.     

Investigation of Drought Trend on the Basis of the Best Obtained Drought Index

Water Resources Management - The drought phenomenon is a primary natural hazard in Iran. The drought can be analyzed using different indices. Therefore, the use of suitable indices will have an...     

An intelligent scheduling system using fuzzy logic controller for management of services in WiMAX networks

The appearance of media applications with high bandwidth and quality of service requirements has made a significant impact in telecommunications technology. In this direction, the IEEE802.16 has defined wireless access systems called WiMAX. These systems provide high-speed communications over a long distance. For this purpose some service classes with QoS requirements are defined; but the QoS scheduler is not standardized in IEEE802.16. The scheduling mechanism has a significant effect on the performance of WiMAX systems for use of bandwidth and radio resources. Some scheduling algorithms have been introduced by researchers; but they only provide some limited aspects of QoS. An intelligent decision support system is therefore necessary for scheduling. In this paper a fuzzy based scheduling system is proposed for compounds of real-time and non-real-time polling services which provide QoS requirements and fairness in dynamic conditions. A series of simulation experiments have been carried out to evaluate the performance of the proposed scheduling algorithm in terms of latency and throughput QoS parameters. The results show that the proposed method performs effectively regarding both of these criteria and achieves proportional system performance and fairness among different types of traffic.     

Corrugated all-composite sandwich structures. Part 1: Modeling

An analytical model for the compressive and shear response of monolithic and hierarchical corrugated composite cores has been developed. The stiffness model considers the contribution in stiffness from the bending- and the shear deformations of the core members in addition to the stretching deformation. The strength model is based on the normal stress and shear stress distribution over each core member when subjected to a shear or compressive load condition. The strength model also accounts for initial imperfections. In part 1 of this series, the analytical model is described and the results are compared to finite element predictions. In part 2, the analytical model is compared to experimental results and the behaviour of the corrugated structures is investigated more thoroughly using failure mechanism maps.     

Extended kalman filter‐based nonlinear model predictive control of a continuous KCl‐NaCl crystallizer

An extended Kalman filter (EKF)‐based nonlinear quadratic dynamic matrix control (EQDMC) for an evaporative cooling draft‐tube baffled (DTB) KCl crystallizer is developed. The controller is used to maintain the productivity, crystal mean size and impurity of crystals. Since these controlled variables are not directly measurable, the EKF is used to estimate them. The nonlinear controller is a combination of an extended linear dynamic matrix control (EDMC) and the quadratic dynamic matrix control (QDMC). This combination provided good control of the system despite the process nonlinearity, constraints, and inadequate reliable online measurement of the controlled variables. The performance of the controller in the presence of plant/model mismatch, disturbance, wrong estimation and simultaneous step changes in the controller setpoints is discussed.     

Applications of the crystallization process in the pharmaceutical industry

The applications of the crystallization technique in the pharmaceutical industry as a purification and separation process for the isolation and synthesis of pure active pharmaceutical ingredients (API), co-crystals, controlled release pulmonary drug delivery, and separation of chiral isomers are briefly discussed using a few case studies. The effect of process variables and solvent on the polymorphism and morphology of stavudine is discussed. The implementation of external control in the form of feedback and real-time optimal control using cooling and antisolvent crystallization of paracetamol in water-isopropyl alcohol is introduced. Two methods to prepare micron-sized drug particles, namely, micro-crystallization and polymer-coated API-loaded magnetic nanoparticles for pulmonary drug delivery, are discussed. The significance of co-crystals in drug administration is highlighted using the theophylline-nicotinamide co-crystal system. Resolution of chloromandelic acid derivatives, a racemic compound, is achieved using direct crystallization and diastereomeric salts crystallization. The crystal structures of diastereomeric salts of chloromandelic acid and phenylethylamine are determined. The structure comparison between the less soluble and more soluble salts shows that weak interactions such as CH/π interactions and van der Waals forces contribute to chiral recognition when the hydrogen bonding patterns are similar.     

A mixing model for diagnosing reacting tracers and tracing reactants in chemical and biochemical processes

It has previously been shown (Tanner et al., 1985) that biochemical and chemical reaction processes of the Type A → B → C can lead not only to kinetic hysteresis between the rate of formation of C and the concentration of species B in batch processes, but also hysteresis between those variables in a closed, imperfectly mixed (two zone) batch reactor. Furthermore, crossplotting the intermediate reactant, B, in one region of the poorly mixed reactor against B from the other major region leads to a clockwise hysteresis curve which is defined by both its area and the coordinate phase angle. This paper shows that the earlier analysis (Tanner et al., 1985) can be extended to the more general system A → B, where A in one region of the vessel is crossplotted against A measured in the other region. With an initial concentration of A* in one zone equal to its highest concentration, the inscribed area double-valued crossplot of A, uniquely defines the system in terms of the inter-vessel flowrate to reaction rate constant ratio, D/k.