Step 1 - First steps
Let's get started with a minimal input file.
#
# Initial single block thermal input
# https://mooseframework.inl.gov/modules/heat_transfer/tutorials/introduction/therm_step01.html
#
[Mesh]
[generated]
type = GeneratedMeshGenerator
dim = 2
nx = 10
ny = 10
xmax = 2
ymax = 1
[]
[]
[Variables]
[T]
[]
[]
[Kernels]
[heat_conduction]
type = HeatConduction
variable = T
[]
[]
[Materials]
[thermal]
type = HeatConductionMaterial
thermal_conductivity = 45.0
[]
[]
[Executioner]
type = Transient
end_time = 5
dt = 1
[]
[Outputs]
exodus = true
[]
Input file
Mesh
We create a simple regular orthogonal mesh block using the GeneratedMeshGenerator. All subblocks under [Mesh] are the so called MeshGenerators. They can be chained together and MOOSE provides a multitude of generators to create and modify meshes. A commonly used MeshGenerator is the FileMeshGenerator, it is used to load a mesh file generated by third party software like Cubit or Gmsh (or sometimes even meshes generated by MOOSE). MOOSE provides a shorthand for the FileMeshGenerator through the "file" parameter inside [Mesh], e.g.
[Mesh]
file = pressure_vessel.e
[]
MOOSE supports a variety of mesh file formats; most commonly used is the Exodus format.
Variables
This top-level block is used to define the variables that are being solved in this model. These variables define spatially varying fields that are defined using a set of degrees of freedom and finite element interpolation functions. MOOSE provides access to a wide variety of methods for defining these variables. The default LAGRANGE variable type is defined at finite element nodes, and interpolated from the values of the connected nodes within an element.
In the case of this model, a single variable is solved. This variable, named T, is the temperature. The name of the variable is defined by the name in the opening brackets of the block ([T]). There is no content in the block in this case because only the default parameters are used.
[Variables]
[T]
[]
[]
Kernels
This top-level block is used to define the kernels that provide volume integrals in the partial differential equation being solved. Generally, a separate Kernel is used to define each term in a partial differential equation. The full heat equation is generally expressed with multiple terms, as described in the Heat Transfer module introduction. However, for this simple example, we are only including the conduction term, so the equation being solve takes the form:
(1)
where is the temperature, is time, is the vector of spatial coordinates, and is the solution domain. Later problems in this series will add the additional terms to the heat equation.
The single [heat_transfer]' block nested in the `Kernels block defines the conduction term in the heat equation defined above. The type = HeatConduction parameter defines the name of the Kernel object that provides that term, and the variable = T parameter defines the variable that the kernel is operating on. There is only one variable in the case of this model, but in a multiphysics simulation, individual kernels would be assigned to operate on specific variables.
[Kernels]
[heat_conduction]
type = HeatConduction
variable = T
[]
[]
Materials
The Materials block is used to define material properties, which are evaluated at the finite element integration points. In general, these material properties can have complex dependencies on the solution variables and other quantities computed by the code, but in this case, a constant values is defined.
The HeatConductionMaterial is a model that provides basic properties used for the terms in the heat equation. In this case, the only property needed is the thermal conductivity, which is defined with a constant value.
[Materials]
[thermal]
type = HeatConductionMaterial
thermal_conductivity = 45.0
[]
[]
Executioner
In the [Executioner] block all parameters relevant to the solution of the current problem are set. type = Transient selects a time-dependent simulation (as opposed to type = Steady). We chose to run for five simulation steps; with a timestep of 1.
[Executioner]
type = Transient
end_time = 5
dt = 1
[]
Outputs
We use the exodus = true shorthand to setup an output object of type Exodus to write an Exodus mesh and solution file to the disk. You can visualize these outputs using Paraview.
[Outputs]
exodus = true
[]
Questions
Units
A question that comes up often is "What units does MOOSE use?".
Look through the input file and try to identify places where units might be relevant.
Expected outcome
Before you run this first input file take a moment to think about what you expect to happen.
Once you've answered the questions and run the first example it is time to move on to a slightly more complex scenario in Step 2.