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Search for the optimal initial composition of the reaction mixture of the polymerization process using artificial immune systems

To establish regularities of polymerization processes, it is advisable to use methods of mathematical modeling. On the basis of mathematical description of the process it is possible to determine the optimal conditions of its course, providing an increase in its efficiency, as well as the quality of produced polymers. One of the problems of optimization of polymerization processes is the problem of determining the initial composition of the reaction mixture, which ensures the achievement of given quantitative or qualitative indicators of the process. The aim of the work is to develop an algorithm for determining the initial concentrations of polymer synthesis reaction. The statement of the problem of searching for optimal concentrations of components of the polymer synthesis process and a numerical algorithm for its solution are given. Since the kinetic model of the polymerization process is an infinite system of ordinary nonlinear differential equations, its solution using classical optimization methods encounters computational difficulties. Therefore, it is proposed to apply the method of artificial immune systems to calculate the optimal initial composition of the reaction mixture of the polymerization process. This method allows to overcome local extrema in multidimensional search spaces and it is easy to implement for a particular process when the number of optimized parameters is changed. The developed algorithm based on the method of artificial immune systems includes a procedure for converting an infinite system of differential equations describing the kinetics of the polymerization process to a finite form using the method of moments. The algorithm has been tested on an industrially significant polymerization process of butadiene on a neodymium-containing catalytic system. The optimum concentrations of reagents that provide the polymer with the desired properties have been calculated. Read more...

Search for a solution to a multi-extremal optimal control problem based on the evolutionary method

When searching for solutions to nonlinear optimal control problems, one may encounter difficulties related to the presence of local extremes. The use of traditional optimization methods is effective in the case of convex problems with the property that the found local extremum is global. Therefore, it is important to develop methods and algorithms for solving multi-extremal optimal control problems. Since the operation of most optimization methods depends on the choice of the initial values of the optimized parameters, it is proposed to apply the method of differential evolution. This method optimizes a set of possible solutions in the range of acceptable values of the desired parameters, the initial values of which are set randomly. The aim of the work is to develop an evolutionary algorithm for finding a solution to a multi-extremal optimal control problem. Overcoming the stuck solution in the local optimum is possible by maintaining population diversity. If the solution falls into the region of the local extremum with an insufficient set number of iterations of the algorithm, an incorrect solution can be obtained. Therefore, in order to dislodge a population from the area of the local extremum, a modification of the differential evolution method is proposed – a dynamic population size. If the population is drawn into the region of a local extremum, then its average fitness changes slightly. In this case, the vectors-individuals with the lowest fitness are removed and new individuals are added. Computational experiments have been carried out on a model optimal control problem with a non-convex reachability domain. The work of the developed evolutionary algorithm is compared with the method of variations in the control space and the algorithm of differential evolution with a constant population size. The effectiveness of the developed evolutionary algorithm in solving a multi-extremal optimal control problem is demonstrated. Read more...