Implementation of the hierarchical approach in the mathematical modelling of once-through steam generators
DOI:
https://doi.org/10.15276/opu.3.62.2020.09Keywords:
once-through steam generator, mathematical modeling, hierarchical structure, heat load, combustion chamber, filter, mixer, separator, feed pumpAbstract
A comprehensive system analysis of a once-through steam generator was carried out as well as a multilevel structure of its model was developed. The application of the procedure of decomposition of a complex object at the initial stages of modeling made it possible to single out multidimensional subsystems of directed action. This makes it possible to use advanced computer simulation software. We distinguished the subsystems of the steam generator as a whole, the subsystem of the steam generator, including the screen tubes, separator, mixer, filter, circulation pump, and connecting pipelines in the resulting structural model. The zones of screen tubes determined by the state of the working medium (heating zone with a single-phase medium, evaporation zone I and evaporation zone II with a two-phase medium), finite-dimensional models of screen tube sections of heating and evaporation zones we considered separately. It was found that the models of zero-level subsystems are described by systems of differential and algebraic equations, between the internal variables of which there is no cause-effect relationship. Any subsystem of the first and higher levels can be represented by a subset of subsystems of the immediately lower levels and a set of oriented connections between them. The principle of recurrent explanation was implemented in the problem of simulating a once-through steam generator. The set-theoretic, matrix and graphical methods are used to describe the relationships between subsystems. It is shown that hierarchical models are forms of description, ready for implementation in high-level programming languages. Systematic analysis of processes, technology and design of a once-through steam generator, as well as the proposed research methodology in the time and frequency domains, the calculation methods and simulation methods used, allows you to select the types and classes of mathematical models, forms of their presentation, as well as software.
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