The Kratos Parameters object is a container based on the well known JavaScript Object Notation (JSON) standard. Even though it can contain any type of key-value information, in Kratos it is used to contain configuration settings for solvers, processes or utilities.
In this tutorial, the use of the JSON format together with the Kratos Parameters class is reviewed using a standard Kratos simulation configuration file (ProjectParameters.json), in this case coming from the FluidDynamicsApplication, as example.
Setup
First of all we need to create a python file with following code to import the Kratos:
from KratosMultiphysics import *
Reading a JSON file
In this subsection we will try to parse the ProjectParameters.json file to construct the Kratos Parameters object. The ProjectParameters.json file reads as follows
{
"problem_data" : {
"problem_name" : "parameters_tutorial",
"model_part_name" : "MainModelPart",
"domain_size" : 2,
"parallel_type" : "OpenMP",
"echo_level" : 0,
"start_time" : 0.0,
"end_time" : 45
},
"output_configuration" : {
"result_file_configuration" : {
"gidpost_flags" : {
"GiDPostMode" : "GiD_PostBinary",
"WriteDeformedMeshFlag" : "WriteDeformed",
"WriteConditionsFlag" : "WriteConditions",
"MultiFileFlag" : "SingleFile"
},
"file_label" : "time",
"output_control_type" : "step",
"output_frequency" : 1,
"body_output" : true,
"node_output" : false,
"skin_output" : false,
"plane_output" : [],
"nodal_results" : ["VELOCITY","PRESSURE"],
"gauss_point_results" : []
},
"point_data_configuration" : []
},
"restart_options" : {
"SaveRestart" : "False",
"RestartFrequency" : 0,
"LoadRestart" : "False",
"Restart_Step" : 0
},
"solver_settings" : {
"solver_type" : "Monolithic",
"model_import_settings" : {
"input_type" : "mdpa",
"input_filename" : "parameters_tuto"
},
"echo_level" : 0,
"compute_reactions" : false,
"dynamic_tau" : 1.0,
"oss_switch" : 0,
"maximum_iterations" : 10,
"relative_velocity_tolerance" : 0.001,
"absolute_velocity_tolerance" : 1e-5,
"relative_pressure_tolerance" : 0.001,
"absolute_pressure_tolerance" : 1e-5,
"volume_model_part_name" : "Parts_Fluid",
"skin_parts" : ["AutomaticInlet2D_Inlet","Outlet2D_Outlet","NoSlip2D_No_Slip_Walls","NoSlip2D_No_Slip_Cylinder"],
"no_skin_parts" : [],
"time_stepping" : {
"automatic_time_step" : false,
"time_step" : 0.1
}
},
"initial_conditions_process_list" : [],
"boundary_conditions_process_list" : [{
"python_module" : "apply_inlet_process",
"kratos_module" : "KratosMultiphysics.FluidDynamicsApplication",
"Parameters" : {
"model_part_name" : "AutomaticInlet2D_Inlet",
"variable_name" : "VELOCITY",
"modulus" : "6*y*(1-y)*sin(pi*t*0.5)",
"direction" : "automatic_inwards_normal",
"interval" : [0,1]
}
},{
"python_module" : "apply_inlet_process",
"kratos_module" : "KratosMultiphysics.FluidDynamicsApplication",
"Parameters" : {
"model_part_name" : "AutomaticInlet2D_Inlet",
"variable_name" : "VELOCITY",
"modulus" : "6*y*(1-y)",
"direction" : "automatic_inwards_normal",
"interval" : [1,"End"]
}
},{
"python_module" : "apply_outlet_process",
"kratos_module" : "KratosMultiphysics.FluidDynamicsApplication",
"Parameters" : {
"model_part_name" : "Outlet2D_Outlet",
"variable_name" : "PRESSURE",
"constrained" : true,
"value" : 0.0,
"hydrostatic_outlet" : false,
"h_top" : 0.0
}
},{
"python_module" : "apply_noslip_process",
"kratos_module" : "KratosMultiphysics.FluidDynamicsApplication",
"Parameters" : {
"model_part_name" : "NoSlip2D_No_Slip_Walls"
}
},{
"python_module" : "apply_noslip_process",
"kratos_module" : "KratosMultiphysics.FluidDynamicsApplication",
"Parameters" : {
"model_part_name" : "NoSlip2D_No_Slip_Cylinder"
}
}],
"gravity" : [{
"python_module" : "assign_vector_by_direction_process",
"kratos_module" : "KratosMultiphysics",
"process_name" : "AssignVectorByDirectionProcess",
"Parameters" : {
"model_part_name" : "Parts_Fluid",
"variable_name" : "BODY_FORCE",
"modulus" : 0.0,
"constrained" : false,
"direction" : [0.0,-1.0,0.0]
}
}],
"auxiliar_process_list" : []
}
and can be parsed to construct a Kratos Parameters object with the next two lines of code
json_file = open("ProjectParameters.json",'r')
ProjectParameters = Parameters(json_file.read())
To visualize the content of the ProjectParameters we need to make the ProjectParameters printable. This can be done by calling the PrettyPrintJsonString method from the ProjectParameters object in this way
print(ProjectParameters.PrettyPrintJsonString())
Working with the Kratos Parameters
Once we have parsed the ProjectParameters.json file, we can start to check, get and edit its information. At this point it is interesting to mention that the Parameters works in a similar manner that a common Python dictionary does. For instance we can extract the solver settings required by the Python solvers by doing
solver_settings = ProjectParameters["solver_settings"]
Similarly, we can do the same operation for a list entry. For instance we can iterate through the entire list of boundary conditions settings as is done below. Note that we have used the method size to obtain the length of the iterated list.
for i in range(ProjectParameters["boundary_conditions_process_list"].size()):
boundary_condition_settings = ProjectParameters["boundary_conditions_process_list"][i]
Complementary, we can check if any field exists before trying to retrieve its value with the Has method. This method returns a boolean variable with value True if the field exists and false otherwise.
ProjectParameters.Has("output_configuration")
To get or modify the value of any field, the Kratos Parameters incorporates the Get and Set methods, which are particularized for all the variable types. Some example of its usage can be found in the lines below.
end_time = ProjectParameters["problem_data"]["end_time"].GetDouble()
domain_size = ProjectParameters["problem_data"]["domain_size"].GetInt()
ProjectParameters["problem_data"]["end_time"].SetDouble(20.0)
ProjectParameters["problem_data"]["model_part_name"].SetString("NewMainModelPart")
Since this is a basic tutorial on the use of the Kratos Parameters object, only the basic features have been described. For more advanced operations check the JSON configuration file tutorial in ([here]pages/(How-to-write-a-JSON-configuration-file) )