Data structure

The data structure in CoCoNuT contains different classes that serve as containers of various types of data that are transferred between the components of CoCoNuT during the partitioned coupling. It consists of the following three classes:

• Model
• ModelPart
• Interface

Model

Model is simply a dict with keys as model part names and values as the reference to model parts. It serves as a container of instances of ModelParts. Additionally, it has one important method called create_model_part, which as the name suggests, creates an instance of the class ModelPart and adds it to the dictionary.

ModelPart

ModelPart is a container of boundary points, that are involved in the partitioned coupling. This contains the initial coordinates- x0, y0, z0 (1D numpy float array), and point ids-id (1D numpy int array). It is recommended to always instantiate ModelPart using the create_model_part method of the class Model, discussed above. Naturally, the size of x0, y0, z0, and id should be equal, which is checked in the __init__ method.

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NOTE:
The data in ModelPart once created, either by __init__ method of the ModelPart class or by create_model_part method of the Model class, cannot be changed later. This is because the initial coordinates of boundary points are always supplied from the solver wrapper, and they don't change during the various stages of the coupling process.

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Interface

Interface stores the variable data that are transferred between the different components (coupling_components) of CoCoNuT to perform partitioned coupling. Additionally, it contains a reference to an instance of Model, usually created in the solver wrapper. As described above, the Model contains several model parts corresponding to the boundaries in the solver wrappers. Therefore, in a way, the interface also contains coordinates of the boundary points that are involved in the coupling.

The data in the interfaces are stored as numpy arrays in a nested dict. The following schematic illustrates the data structure in the Interface class, where the arrow points from a key to the value in the dict:

For example, in the schematic above, the interface has a model part named "mp_1_name", which has several variable data. The data for the variable var_1 is stored in a numpy array with the number of rows equal to the number points in the model part and the number of columns equal to the number of components/dimensions of the variable. The number of dimensions for a variable is defined in the variable_dimensions dict in the file data_structure/variables.py variables.py, for example, the number of dimensions for the variables pressure and displacement is 1 and 3, respectively.

The nested dict in the Interface is constructed during the instantiation of the class using a parameters dict given as an input argument. For the schematic shown above, the parameters dict would be:

[
  {
    "model_part": "mp_1_name",
    "variables": [
      "var_1",
      "var_2",
      ..
    ]
  },
  {
    "model_part": "mp_2_name",
    "variables": [
      "var_3",
      ..
    ]
  },
  .
  .
  .
]

The data in the interface can be accessed, added, or replaced by the various methods implemented in the Interface class, which can be looked in the file data_structure/interface.py.

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NOTE:
The file data_structure/variables.py does not contain a class definition. It has a dict called variable_dimensions with keys as data variable names (string) and values as the number of components or dimensions (int). One important point to note is that only variables defined in this dictionary can be used in CoCoNuT. To use a new variable, the user first needs to add the variable name and its number of components in this dict.

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