Python Script Tutorial: Reading ModelPart From Input File

The ModelPart represents an arbitrary part of the Model to be simulated and stores the mesh and additional data for it. Most of the Kratos routines take a ModelPart as their argument. So always is necessary to create and fill a ModelPart. In this tutorial we will describe how to create and fill a model part from given input file.

Setup

First of all we need to create a python file with following code to import the Kratos:

from KratosMultiphysics import *
from KratosMultiphysics.FluidDynamicsApplication import *

Creating a ModelPart

To create a ModelPart, one has to create a new Model first, and then to call its constructor passing the `ModelPart``s name as its argument:

this_model = Model()
fluid_model_part = this_model.CreateModelPart("FluidPart")

You can print the fluid_model_part:

>>> print(fluid_model_part)
-FluidPart- model part
    Buffer Size : 1
    Number of tables : 0
    Number of sub model parts : 0
    Current solution step index : 0

    Mesh 0 :
        Number of Nodes      : 0
        Number of Properties : 0
        Number of Elements   : 0
        Number of Conditions : 0

It can be seen that the ModelPart is empty and has the buffer size equal to 1. This means that no history of the nodal solution steps variables will be saved.

The next step is to define the variables we want to store as historical variables in nodes of this ModelPart as follow:

fluid_model_part.AddNodalSolutionStepVariable(VELOCITY)
fluid_model_part.AddNodalSolutionStepVariable(PRESSURE)

Reading ModelPart File

The input file of the Kratos has .mdpa (stand for ModelPart) and contains the properties, nodes, elements, conditions and initial values. A convenient way to create this file is to use the interface prepared for GiD pre and post processor. Here you can find more information about the input file. Here we assume that the Cylinder.mdpa input file is already created using GiD:

For reading the .mdpa file first we have to create a ModelPartIO object passing the input file path/name to its constructor:

fluid_model_part_io = ModelPartIO("path/to/file/example")

NOTE: the file name is used without the .mdpa extension!

Then use this IO object to read the file and store the mesh and data in ModelPart:

fluid_model_part_io.ReadModelPart(fluid_model_part)

And printing again the ModelPart:

 >>> print(fluid_model_part)
 StructurePart model part
-FluidPart- model part
    Buffer Size : 1
    Number of tables : 0
    Number of sub model parts : 5
    Current solution step index : 0

    Mesh 0 :
        Number of Nodes      : 3072
        Number of Properties : 2
        Number of Elements   : 5778
        Number of Conditions : 366

    -NoSlip2D_No_Slip_Cylinder- model part
        Number of tables : 0
        Number of sub model parts : 0

        Mesh 0 :
            Number of Nodes      : 126
            Number of Properties : 0
            Number of Elements   : 0
            Number of Conditions : 126
    -Parts_Fluid- model part
        Number of tables : 0
        Number of sub model parts : 0

        Mesh 0 :
            Number of Nodes      : 3072
            Number of Properties : 0
            Number of Elements   : 5778
            Number of Conditions : 0
    -AutomaticInlet2D_Inlet- model part
        Number of tables : 0
        Number of sub model parts : 0

        Mesh 0 :
            Number of Nodes      : 21
            Number of Properties : 0
            Number of Elements   : 0
            Number of Conditions : 20
    -Outlet2D_Outlet- model part
        Number of tables : 0
        Number of sub model parts : 0

        Mesh 0 :
            Number of Nodes      : 21
            Number of Properties : 0
            Number of Elements   : 0
            Number of Conditions : 20
    -NoSlip2D_No_Slip_Walls- model part
        Number of tables : 0
        Number of sub model parts : 0

        Mesh 0 :
            Number of Nodes      : 202
            Number of Properties : 0
            Number of Elements   : 0
            Number of Conditions : 200

Setting the Buffer Size

If we need to store the values of the nodal solution step variables in previous time steps, we must modify the buffer size AFTER defining the historical variables:

fluid_model_part.SetBufferSize(2)

This would store the values for two previous steps in addition to the current ones.

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