Week 2 Bevel Gear Challenge
GRID DEPENDENCY TEST
Grid dependency test involves verifying the simulated results are significantly affected by the mesh size. This is crucial for ensuring the accuracy, efficiency and reliability of the simulations.
First we run the simulation with a coarse mesh and starts refining the mesh and run the simulation again until the results wont change. This way we can conform the correct mesh size.
Mesh refinement is also called a Grid Dependency Test.
USES
1. Ensure Reliable Results.
2. Optimization of computational resources.
3. Improving model understanding.
By varying the mesh, we can gain deeper insight into how the underlying physics of the problem respond to different levels of discretization.
REPORT
AIM
To perform grid dependency test for the given bevel gear simulation. And solve for von-mises stress, equivalent elastic strain and total deformation for the mesh sizes 4, 5, and 6mm.
CASE 1
Open ANSYS workbench and import bevel gear model. For this simulation we are using structural steel. The properties of the material is given below,
Open the model in space claim software and increased the diameter of the holes to 45mm and 25mm otherwise there will be convergence issue.
Then the model is opened in mechanical software. Renamed them as big and small according to the sizes.
Assigned contact and target faces and there are total 40 faces. Set the other parameters as below,
Type Frictional
Behaviour Symmetric
Formulation Augmented Lagrange
Interface treatment Adjust to touch.
Inserted body to ground- revolute joints for big and small gears.
Analysis setting
Give values as below,
Simulation is running through 6 steps.
No. of steps = 6
Auto time stepping = ON
Defined by = Time
Initial time step = 0.2s
Minimum time step = 0.1s
Maximum time step = 1s
Large deflection = ON
JOINT LOADS
Insert two joint loads.
Select the big gear 'Revolute- Ground to Big' and give moment to this gear. Give a moment of 100Nm to all steps.
Select the small gear 'Revolute- Ground to small' and give rotation of 120 degree to it through 6 steps by incrementing 20 degrees with each steps.
In this case giving 4mm mesh and face sizing of 1.75mm to all the 40 contact region.
RESULTS
Requested for equivalent stress, total deformation and equivalent elastic strain.
Equivalent stress
Equivalent strain
Total deformation
CASE 2
In case 2 the mesh size is 5mm and face sizing is 1.75mm like case 1. All other procedures are same as case 1.
Equivalent stress
Equivalent strain
Total deformation
Case 3
EQUIVALENT STRESS
In this case 6mm mesh is used and a face sizing of 1.75mm like case1. All other procedures are same as case 1.
Equivalent strain
Total deformation
CONCLUSION
The grid dependency test was conducted on bevel gear with different mesh sizes of 6mm, 5mm, 4mm. The result of 3 cases are tabulated below,
CASE Equivalent stress Equivalent Total (max) Elastic Deformation Strain (max) (max)
Case 1 450.72MPa 0.0028213 47.902mm (4mm)
Case 2 401.18MPa 0.0026522 47.902mm (5mm)
Case 3 355.91MPa 0.0020105 47.902mm (6mm)
The finest mesh size of 4mm had the greatest maximum equivalent stress and maximum elastic strain values when comparing each of the cases. The deformation remains the same for all cases.
The grid dependency test has been conducted, When running it on this bevel gear, we can improve the accuracy of the results by changing the mesh size. We can see that refining the mesh size from 6mm to 5mm and then 4mm the equivalent stress and elastic strain is merging towards accurate value. Running the simulation further by refining mesh size would produce more accurate results.
Here we can choose 5mm mesh because the difference in strain between 5mm and 4mm is very small compared to 5mm and 6mm and 4mm mesh requires more computing time.