Entities creation from scratch

Entities creation from scratch

Here we present the interface in order to create new entities in an empty model from Python.

Creating nodes

We can create a node by doing. If we Try to create a new node with the same Id and different coordinates we would get an error.

main_model_part.CreateNewNode(1, 1.0,0.0,0.0)
#main_model_part.CreateNewNode(1, 0.0,0.0,0.0)  # Here an error is thrown

However if we try to create a node with the same coordinates twice nothing is actually done (and no error is thrown)

main_model_part.CreateNewNode(1, 1.00,0.00,0.00) 
print(main_model_part.NumberOfNodes()) # This still returns 1!!

We can now access the node as needed, for example:

print(main_model_part.GetNode(1).Id) # Gives 1
print(main_model_part.GetNode(1,0).X) # Gives 1.0

Nodes can be created in every order

main_model_part.CreateNewNode(2000, 2.00,0.00,0.00)
main_model_part.CreateNewNode(2, 2.00,0.00,0.00)

We could then loop over all the nodes:

for node in main_model_part.Nodes:
    print(node.Id, node.X, node.Y, node.Z)

Or eventually remove nodes one by one by doing:

main_model_part.RemoveNode(2000)

Let’s now see what happens if we add a node to a submodelpart. Here the node will be both in root ModelPart and “BC”, but for example not in derived submodelparts from “BC” or root ModelPart.

bc_model_part = main_model_part.GetSubModelPart("BC")
bc_model_part.CreateNewNode(3, 3.00,0.00,0.00)

Multiple nodes can be removed at once (and from all levels) by flagging them:

for node in main_model_part.Nodes:
    if node.Id < 3:
         node.Set(KratosMultiphysics.TO_ERASE,True)   
main_model_part.RemoveNodesFromAllLevels(KratosMultiphysics.TO_ERASE)

One could call simply the function RemoveNodes and remove them from the current level down.

Creating Elements and Conditions

Elements and Conditions can be created from the python interface by providing their connectivity as well as the Properties to be employed in the creation. The string to be provided is the name by which the element is registered in Kratos. An error is thrown if i try to create an element with the same Id

main_model_part.AddProperties(KratosMultiphysics.Properties(1))
main_model_part.CreateNewElement("Element2D3N", 1, [1,2,3], main_model_part.GetProperties()[1])

An identical interface is provided for Conditions, as well as functions equivalent to the nodes for removing from one level or from all the levels.

Creating MasterSlaveConstraints

The case of the constraints, like it requires the existance of DoF we will create a new model part in order to avoid problems. This example will advance some methods that will be introduced in future sections, as AddNodalSolutionStepVariable. The current interface for python works directly with nodes, it is not possible to manipulate DoF manually.

mp = this_model.CreateModelPart("constraint_example")

mp.AddNodalSolutionStepVariable(KratosMultiphysics.DISPLACEMENT)
mp.AddNodalSolutionStepVariable(KratosMultiphysics.REACTION)

mp.CreateNewNode(1, 0.00000, 0.00000, 0.00000)
mp.CreateNewNode(2, 0.00000, 1.00000, 0.00000)

KratosMultiphysics.VariableUtils().AddDof(KratosMultiphysics.DISPLACEMENT_X, KratosMultiphysics.REACTION_X, mp)

mp.CreateNewMasterSlaveConstraint("LinearMasterSlaveConstraint", 1, mp.Nodes[1], KratosMultiphysics.DISPLACEMENT_X, mp.Nodes[2], KratosMultiphysics.DISPLACEMENT_X, 1.0, 0)