Introduction to codedoc.

The codedoc has been generated using Sphinx from the docstrings in the code.

The text below provides a high-abstraction-level introduction to the FONSim codebase.

Main parts

FONSim consists of nine main parts. Each part is discussed briefly.

  • core: This is the network simulation functionality. It is written agnostically of the domain (fluidic, eletric, …) to be simulated. This core is discussed in detail further on.

  • components: The standard library of fluidic components with actuators, tubes, restrictors, sources etc.

  • wave: Signal generators: block wave, sine wave etc.

  • data: Functionality for handling data. The files,, and ease working with pv-curves, including reading them in from CSV files. The simulation data export functionality resides in

  • fluid: Defines how fluids should be specified in the form of class definitions. Currently supported are ideal gasses and incompressible liquids.

  • fluids: Standard library of fluids with air, water etc.

  • visual: Plotting functionality specific to visualizing simulation results.

  • conversion: String comparison and unit conversion.

  • constants: Physical constants.

  • resources: Data files such as pv-curves in CSV format, mostly used in examples and tests.


The core contains all functionality that is required for simulating networked system but, as it is written domain-agnostic, it does not contain any code specific to fluidic system.

The core consists of seven files, each discussed here.


    Class definition of Variable. Variable objects are used to tell to the solver that there is a yet unknown timeseries of numerical scalar values that will have to be solved for during the simulation. After running the simulation, for each Variable object a 1D array of values will have been derived that satisfies the given equations best. To put it simply, the solver uses the Variable objects to keep reference of what numerical value belongs to what equations.

    A Variable has a key to indicate the medium it refers to (for example, pressure, massflow, or temperature). It also has an orientation to indicate which network equations should be applied when it is connected to other components (or when it is used stand-alone).


    Class definition of Terminal. A Terminal contains one or more Variable instances that are often used alongside each other. A Terminal can be connected to another terminal. The solver automatically generates the network equations (which relates the Variables of different components to each other) from how the terminals are connected to each other. Therefore, the Variables in a Terminal should be defined such that they make physical sense.

    In practice this often leads to two Variables, one with orientation across and another with orientation over. Examples of typical pairs and their domain include pressure and massflow (fluidic), voltage and current (electric), linear displacement and force (mechanical, linear), rotational displacement and torque (mechanical, rotational).


    Class definition of the base class Component. This class definition provides the functionality common to all components. Usable components such as actuators, sources etc. inherit from this base class and add the relevant Variables, Terminals and internal equations. In practice, the class Component is never instantiated, as doing so would create a component without any physical usefulness.

  • and

    Class definitions of respectively System and Node. A System object holds information on which components it contains and how they are connected to each other. A connection between two terminals (a connection is always between terminals, not between components) is recorded in a Node object. A Node class instance contains of data only a list of Terminals it is connected to, the Node class mostly defines functionality to manipulate Node objects.

    While it is usual to say that x terminals are connected to each other, in the simulator this is handled by connecting those x terminals to a common node. Each Node instance therefore contains the Terminals the Node is connected to. A Terminal is always connected to a Node, and vice-versa. A Terminal may not be connected to more than one Node. A Terminal does not know to which Node it is connected, this information is only stored in the nodes.


    Class definition of Simulation. This class provides functionality for:

    • Deriving mathematical constructs from a relationally-specified System object: matrices, listing all equations etc.

    • Evaluating all component equations

    • Memory management

    • Starting the the numerical simulation

    For solving the resulting system of equations it uses a solver. The solvers are defined in

    Putting the relationally-specified System object in a mathematical form is a computationally intensive task and is done only once during the initialization thanks to a cache system.


    Numerical solvers. These solvers assume particular functionality of the class Simulation.