Object-oriented design of process line simulation and optimization—A case study in papermaking

Simulation-based optimization for industrial process lines is discussed in this paper. Our approach combines multidisciplinary modeling, modern sensitivity analysis methodology as well as multiobjective optimization by means of object-oriented software design principles. As a result, a simulation and optimization approach that can be extended and modified due to users’ needs can be developed. Our approach is illustrated by a real-world example from papermaking industry.     

Phase diagram and thermodynamic properties of the LaI3–RbI binary system

Differential Scanning Calorimetry (DSC) method was used to determine phase equilibria in the LaI₃–RbI binary system, and heat capacity of LaI₃ and compounds existing in the system under investigation. Two compounds were identified in the solid phase of this system. First of them, Rb₂LaI₅, melts incongruently at 809 K. The second one, Rb₃LaI₆, forms at 686 K from Rb₂LaI₅ and RbI, undergoes a solid-solid transition at 706 K and melts congruently at 864 K. The compositions of RbI–Rb₃LaI₆ and Rb₂LaI₅–LaI₃ eutectics corresponding to LaI₃ mole fraction of x = 0.177 (T = 789 K) and x = 0.472 (T = 773 K), respectively were found from Tammann's diagrams. The LaI₃–RbI pseudobinary system was also optimized by CAPLHAD method. Thermodynamic properties of the liquid phase were modelled using Associate Solution Model.     

Phase diagram and thermodynamic properties of the GdBr3–CsBr binary system

Phase diagram of the GdBr₃-CsBr binary system was established by Differential Scanning Calorimetry (DSC) method. This system exhibits three stoichiometric compounds, namely Cs₃GdBr₆, Cs₃Gd₂Br₉ and CsGd₂Br_7; and three eutectics located at GdBr₃ molar fraction x = 0.11 (T = 847 K), x = 0.52 (T = 798 K) and x = 0.72 (T = 859 K), respectively. Cs₃GdBr₆ undergoes a solid–solid phase transition at 701 K and melts congruently at 1077 K. Cs₃Gd₂Br₉ melts incongruently at 841 K and finally CsGd₂Br₇ undergoes a solid–solid phase transition at 788 K and melts congruently at 880 K. Experimentally determined phase diagram was optimized by CALPHAD method and thermodynamic properties of compounds existing in the system were estimated. Phase transition of pure GdBr₃were determined at 533 K and ΔH_tr = 0.41 kJ mol^-1.     

Computer simulation studies of recombination of ions in multi ion-pair ensembles—I. Diffusion-controlled processes

The problem of the diffusion-controlled recombination of ions for the case in which initially two or more non-separable pairs of oppositely charged ions are present in the system is treated by means of a computer simulation method.In the first part of the project, the calculations were performed for the media with the short mean free path of the free movement of ions between scattering events, i.e. for the conditions of the diffusion model of the ion transport. The movement of an ion is simulated by a superposition of random walk and drift in the electric field of all the other ions in the system. Thus, the calculations belong to the class of stochastic dynamics methods.The simulations assumed the partition of an ion ensemble into small independent clusters of up to ten ion pairs. Results were obtained on the probability of ion survival as a function of time and the probability of ion escape from recombination at infinite time. The scale of the deviations of the kinetics of the recombination process in the multi-pair clusters from the kinetics for the isolated pairs was estimated. Another series of the computer experiments simulate diffusion-controlled recombination (annihilation) of ions in model supersaturated solutions with different concentrations of ionic solutes and different dielectric constant of the solutions. The simulations yield the ion survival probability as a function of time and allow us to calculate the rate constant of the ion recombination as a function of the ion concentration.     

Computer simulation studies of recombination of ions in multi ion-pair ensembles—II. Processes characterized by long mean free paths of charged species

The problem of the recombination of charged species for the case in which initially one or more non-separable pairs of oppositely charged ions are present in the system is treated by means of computer simulation method.The calculations of the electron–cation recombination in the systems characterized by long mean free path (MFP) of an electron between the scattering events were performed. The calculations of the recombination kinetics and escape probability for single pairs were compared with the Debye–Smoluchowski–Onsager theory. It was found that for large MFPs, of above 10–20% of the Onsager distance in the medium, the theory based on the diffusion model is no longer valid, even for isolated ion pairs.The multi-pair effects were investigated by simulation of the electron–cation recombination in clusters composed of up to ten pairs. The deviations of the multi-pair kinetics and escape probability from the corresponding single-pair results are significant.In a series of preliminary calculations it was found that, in contrast to the processes characterized by short MFPs, the mechanism of the energy and momentum transfer during the electron scattering process influences very significantly both the recombination kinetics and the escape probability.     

CONORBIT: constrained optimization by radial basis function interpolation in trust regions†

This paper presents CONORBIT (CONstrained Optimization by Radial Basis function Interpolation in Trust regions), a derivative-free algorithm for constrained black-box optimization where the objective and constraint functions are computationally expensive. CONORBIT employs a trust-region framework that uses interpolating radial basis function (RBF) models for the objective and constraint functions, and is an extension of the ORBIT algorithm [S.M. Wild, R.G. Regis and C.A. Shoemaker, ORBIT: optimization by radial basis function interpolation in trust-regions, SIAM J. Sci. Comput. 30 (2008), pp. 3197–3219]. It uses a small margin for the RBF constraint models to facilitate the generation of feasible iterates, and extensive numerical tests confirm that such a margin is helpful in improving performance. CONORBIT is compared with other algorithms on 27 test problems, a chemical process optimization problem, and an automotive application. Numerical results show that CONORBIT performs better than COBYLA (Powell 1994), a sequential penalty derivative-free method, an augmented Lagrangian method, a direct search method, and another RBF-based algorithm on the test problems and on the automotive application.     

Beyond binary correctness: Classification of students’ answers in learning systems

User Modeling and User-Adapted Interaction - Adaptive learning systems collect data on student performance and use them to personalize system behavior. Most current personalization techniques focus...     

The power of computational thermochemistry in high-temperature process design and optimization: Part 1 — Unit operations

Industrial process modeling is increasingly accessible through computational chemistry packages. Computational Thermochemistry (CT) is particularly convenient for exploring the behavior of high-temperature processes (e.g., pyrometallurgical unit operations such as calciners, roasters, smelters, converters, and electric arc furnaces) since their operating conditions are mostly dictated by local/global thermodynamic phase equilibria. Under these high-temperature conditions, energy barriers are small and do not limit the kinetics of many chemical reactions. In this context, engineers-in-training must take full advantage of CT to explore and understand current unit operations in high-temperature manufacturing technologies. This work illustrates the strength of computational thermochemistry for high-temperature modeling through four case studies, i.e., 1. a carbo-reduction process, 2. a glass production/recycling furnace, 3. an aluminothermic reactor for the production of a ferroniobium alloy, and 4. a titanium purification unit. Moreover, the relevance of key fundamental thermodynamic concepts is discussed through the modeling of these unit operations. All the thermodynamic simulations presented in this work were performed using FactSage, a metallurgy-specialized thermochemical package widely employed in both academia and industry.     

Free vibration analysis and shape optimization of variable thickness plates and shells—II. Sensitivity analysis and shape optimization

In this paper an automated approach is used to carry out sensitivity analysis and to obtain optimum shapes for plates and shells in which the natural frequencies are maximized. The free vibration analysis is carried out with the nine-noded, degenerated, Huang-Hinton shell element implemented and tested in Part I of this paper. Design variables that specify either the shape or thickness distribution of the structures are considered. Special attention is focused on the sensitivity calculations and problems connected with their accuracy and performance are highlighted when the semi-analytical and finite difference methods are used. Advantages and disadvantages of each method are discussed. The optimal solution is found by the use of a structural optimization algorithm which integrates the finite element module (Part I), sensitivity analysis and a mathematical programming method: sequential quadratic programming (SQP). Optimal forms are then obtained for a set of benchmark examples using the two sensitivity analysis techniques and their results are compared. The results obtained for optimum solutions in the present paper justify the usage of the semi-analytical method for sensitivities calculations for structural shape optimization purposes.     

Exact truss topology optimization: allowance for support costs and different permissible stresses in tension and compression—extensions of a classical solution by Michell

The aim of this paper is twofold. It introduces a theory of Michell trusses taking support (reaction) costs into consideration, which is illustrated with a modified version of Michell’s best known example. Then eight other variations on this example are presented, with (i) equal or unequal permissible stresses in tension and compression, (ii) the structural domain consisting of a half-plane or a full plane, and (iii) the supports being two pins, or a pin and a roller. Previously noted shortcomings of Michell’s theory are highlighted and several fundamental properties of non-selfadjoint topology optimization problems discussed. The analytical solutions are verified to a high degree of accuracy by numerical results.     

A review of: “The Time-span of Discretion in Job Analysis”. By J. M. It. Hillo.;. Tavistock Pamphlets No. 1. London: Tavistock Publications. A reprint,of an article in Human relations,Vol. IX,No. 3. Pp. 20. 3s. 6d.

Using a newly developed telemetry system, records of heart-rate reaction of human subjects prior to the rope climb were obtained. The data presented on humans represents support for research by Rushmer, who experimented with dogs in demonstrating the role of the motor cortex in controlling the heart boat and particularly its involvement prior to vigorous exercise. The data consists of telemetered heart rates of 10 gymnasts prior to, during and following a rope climb for speed. The percentage of anticipatory heart rate increase over basal value of post-warm-up for the climb was approximately 25 per cent. This amount of anticipatory heart rate for the 10 subjects unassociated with actual energy expenditure would permit support of Rushmer's theory.