The following picture shows what should be visible after importing the tutorial project.
Figure 2: Workbench view.
1.1 Create the Simulation
The first step you will do is to create the simulation.
Figure 3: Geometry dialog box.
Hitting the ‘Create Simulation’ button leads to the following options:
Figure 4: Simulation list.
Choose Thermomechanical as analysis type and click the ‘Create Simulation’ button to confirm. After that, a simulation tree showing you all the necessary steps to set up all your simulation will show in your workbench.
Figure 5: Simulation tree.
1.2 Create Topological Entity Sets
Prior to setting up the simulation, we recommend creating topological entity sets. You can do this at any point of the simulation setup, however, it is easier to do it in the beginning.
The sets for the top, the rings and the ring grooves have already been created for you according to the following picture:
Figure 6: Overview of entity sets.
Now, you will only need to create the set for the interior and the skirt of the piston, which is everything other than what is already assigned to sets. Here are the steps that you can follow:
Figure 7: Steps to create entity set.
Hide all the existing topological entity sets.
Activate the box selection.
Select all remaining parts.
Hit the ‘+’ next to Topological Entity Set and give it a name.
Find out more
You can find out more regarding our viewer in the following link: Viewer Tips & Tricks
2. Assigning the Material and Boundary Conditions
In this section we will define the physics of our model.
2.1 Model (Gravity)
In the first step, we define the magnitude and direction of the gravity by assigning the values below:
Figure 8: Model dialog box.
The magnitude of the gravity that we use is 9.81 \(m^2/s\) in the direction -1 in \(e_y\).
2.2 Define a Material
Afterwards, we will define the material of our piston and we will use Aluminium as the material.
Figure 9: Material list.
2.3 Assign the Boundary Conditions
A thermomechanical analysis will need two boundary conditions which are the thermal boundary conditions and the mechanical boundary conditions we will set up both in this section.
a.Thermal Boundary Conditions
We will use a Convective heat flux boundary condition as our thermal boundary conditions. You can therefore add a boundary condition by hitting the ‘+’ and select ‘Convective heat flux boundary’ condition:
Figure 10: Boundary conditions.
Following the above instructions open the setup options for convective heat flux. We will define them according to the picture below:
Figure 11: Convective heat flux boundary condition for the top of the piston.
Firstly, you can set the \(T_0\) Reference temperature as 741 \(°C\) and the Heat transfer coefficient as 450 \(W/(K.m^2)\).
Next, you will need to define the surface where the boundary condition is applied. For example, this is the boundary condition for the top of the piston.
Follow this procedure for each row within the table below:
Entity Set
Reference temperature [°C]
Heat transfer coefficient [W/(K*m^2)]
Top
741
450
Ring 1
180
150
Groove – Ring 1
180
1000
Ring 2
160
150
Groove – Ring 2
160
400
Ring 3
140
150
Groove – Ring 3
140
400
Interior and skirt
120
650
Table 1: Convective heat flux boundary conditions for engine piston.
b. Mechanical Boundary Conditions
Now it is time for the mechanical conditions, which are three pressure definitions (top and the first two rings) and two remote displacements. For example, we will assign a pressure boundary condition to the top of the piston.
Figure 12: Pressure boundary condition.
By following the same process as before, you can select the pressure boundary condition in the lists of boundary conditions. After that, we will use a pressure value of 2e7 \(Pa\) at the top face of the piston. The pressure boundary conditions for the other parts can be seen in the table below:
Entity
Pressure [Pa]
Ring 1
14e7
Ring 2
4e6
Table 2: Pressure boundary conditions.
Now, you can create the two remote displacements and give them the following properties:
Figure 13: Remote Displacement for top side of piston
For the first remote displacement, we will apply it at the top pin of the piston with coordinate of the external points:
x: 0 \(m\)
y: -0.042 \(m\)
z: 0.02028 \(m\)
Figure 14: Remote displacement for bottom side of pisotn
For the second remote displacement at the opposite side of the piston, the remote point will have the coordinates:
x: 0 \(m\)
y: 0.042 \(m\)
z: -0.01992 \(m\)
Now all boundary conditions are assigned and we can proceed to creating the mesh.
3. Mesh
We will use the standard algorithm for our mesh, which is a good choice in general as it is quite automated and delivers good results for the most geometries. For this tutorial, we will generate a second order mesh.
You will only need to change the Sizing to Manual and set our maximum edge length as 1.8e-3 m and enable the 2nd order elements toggle. Make sure your setting look like the picture below:
Figure 15: Second order mesh settings
When the mesh has been generated, you can observe your mesh. The mesh will look like this:
Figure 16: Generated second order mesh
If we create a first order mesh, it will visually look exactly like the second order mesh, because the cell count is the same for both. However the second order mesh has additional nodes inbetween two connecting nodes, which helps to model deformations more accurate.
4. Start the Simulation
Finally, you can run your thermomechanical analysis for the engine piston and you can do this by clicking the ‘+’button to start a simulation run.
Figure 17: Step to run a simulation.
Moreover, you can change the name of your simulation to your liking and start the simulation by clicking ‘Start’
Figure 18: New run dialog box.
Did you know?
Since we have generated two different mesh, we can select each mesh and run a simulation for each mesh simultaneously.
5. Post-Processing
After the simulation has finished, you can access the simulation results by clicking ‘Post-process results’ in your run dialog box or by going into the Solution fields and you will be redirected to the post-processor.
Figure 19: Access to simulation results.
You can choose what properties to visualize by going into Results and choose which property to visualize. For example, we will show the Temperature and the von Mises stress in this tutorial.
Figure 20: Results tree,
Below is the temperature distribution of the piston:
Figure 21: Temperature distribution,
We can also see the von Mises stress distribution below:
Figure 22: Von Mises stress ditribution
Congratulations! You finished the thermomechanical analysis of an engine piston tutorial!
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