How to avoid rigid motion for thermal stress simulaitons?
I’m conducting transient simulation to see the effect of residual stress due to the solidification and cooling of an engine block.
The temperature profile is obtained using ANSYS Fluent.
The following figure represents a simplified version of the geometry I’m using. The engine block is represented in green color and the cooling chills are represented in pink color.
The engine block is cast using an aluminum alloy and the cooling chills are made from steel. Due to the difference in thermal expansion, I’m expecting the cooling chills to be always in contact with the engine block.
For the engine block, I’m using a bilinear material model with data for different temperatures (the material model was checked for a simplified stress lattice model for convergence). And for the cooling chills a non-linear material model us used.
For the engine block, I need it to freely contact the chills so I will not expect any undesirable stress due to over-constraining the model. Therefore, the geometry (all the bottom faces of the engine block and the chills) is only constrained in Y-axis using a displacement constrain.
The temperature will start from around 700C at zero time step and cool down to room temperature.
Initially, there is no penetration between the engine block and the chills therefore I’ve used “adjust to touch” as the interface treatment. All contacts have the same settings.
I have used contact sizing to have the same mesh size between the engine block and the chills contact surface. However, there are a few areas where the nodes do not match. I’ve tried using “contact match control” but it did not work to resolve the unmatched nodes
The current issue I have,
1. Element distortion at the contact.
2. Cooling chills having rigid motion.
What I have done to,
1. Reduced normal stiffness factor from 1 to 0.1
2. Changed the detection method “nodal-normal from contact”
3. Changed update stiffness to “each-iteration, aggressive”
4. Increased the stabilization damping factor from 0 to 1E-5.
5. Turned on week springs, increased the damping from 1 to 10 to avoid rigid motion.
6. Increased time step, initial to 10 and maximum to 100.
What I want to know,
1. It’s obvious that with the current boundary conditions the engine blocks will have rigid motion. But is there any other way to constrain the model without influencing the thermal expansion or contraction?
2. After all this I’m still getting rigid motion is there another way to solve this issue?