Component-oriented acausal modeling of the dynamical systems in Python language on the example of the model of the sucker rod string

• Published in: PeerJ. Computer science Vol. 5; p. e227
• Main Authors: Kopei, Volodymyr B., Onysko, Oleh R., Panchuk, Vitalii G.
• Format: Journal Article
• Language: English
• Published: United States PeerJ. Ltd 28.10.2019; PeerJ, Inc; PeerJ Inc
• Subjects: Acausal modeling; Adequacy; Algebra; Algorithms; Algorithms and Analysis of Algorithms; Applied research; Complex systems; Complexity; Component-oriented modeling; Computer Education; Computer models; Computer simulation; Difference equations; Differential equations; Dynamical system; Dynamical systems; Hybrid modeling; Hydraulics; Libraries; Mechanical components; Modelling; Ordinary differential equations; Programming Languages; Python; Python (Programming language); Scientific Computing and Simulation; Software Engineering; Solvers; Strings; Symbolism; Values; Variable structure system; Variables; Sucker rod string; Multi-domain modeling; Difference equations; Acausal modeling; Variable structure system; Hybrid modeling; Component-oriented modeling; SymPy; Dynamical system; Python
• ISSN: 2376-5992; 2376-5992
• DOI: 10.7717/peerj-cs.227

Typically, component-oriented acausal hybrid modeling of complex dynamic systems is implemented by specialized modeling languages. A well-known example is the Modelica language. The specialized nature, complexity of implementation and learning of such languages somewhat limits their development and wide use by developers who know only general-purpose languages. The paper suggests the principle of developing simple to understand and modify Modelica-like system based on the general-purpose programming language Python. The principle consists in: (1) Python classes are used to describe components and their systems, (2) declarative symbolic tools SymPy are used to describe components behavior by difference or differential equations, (3) the solution procedure uses a function initially created using the SymPy lambdify function and computes unknown values in the current step using known values from the previous step, (4) Python imperative constructs are used for simple events handling, (5) external solvers of differential-algebraic equations can optionally be applied via the Assimulo interface, (6) SymPy package allows to arbitrarily manipulate model equations, generate code and solve some equations symbolically. The basic set of mechanical components (1D translational “mass”, “spring-damper” and “force”) is developed. The models of a sucker rods string are developed and simulated using these components. The comparison of results of the sucker rod string simulations with practical dynamometer cards and Modelica results verify the adequacy of the models. The proposed approach simplifies the understanding of the system, its modification and improvement, adaptation for other purposes, makes it available to a much larger community, simplifies integration into third-party software.