Kelvin-Voigt Boundary Benchmark Case

[cgeudeker]

Describe the PR
This is a benchmark case to test the Kelvin-Voigt boundary addition.

Related Issues/PRs
Kelvin-Voigt Boundary Implementation for #692

Additional context
General Notes: The mesh represents a 1m column loaded with 1000 rows and 6 cells in each row. The boundary conditions are 1 kN particle surface traction applied to the top, roller boundaries along the sides of the columns and the Kelvin-Voigt boundary at the base.

There are three different particle files with varying densities (6000, 24000, and 54000 particles). These files have associated with respective entity sets for the application of particle surface traction.

Also, in these files, the absorbing boundary and velocity constraint are both placed on the bottom corner nodes.

[jgiven100]

@cgeudeker Thanks for uploading!

[jgiven100]

@cgeudeker Couple thoughts:

1. We might want to simplify these inputs to a single case (i.e., remove different particle densities)
2. The 0.1 m model will run much faster as a benchmark and shows the same successful implementation
3. Including an jupyter notebook that shows the displacement converges to the analytical value will be good (e.g., when \delta=0.1 diplacement converges to 0.0001 meters)

[jgiven100]

@cgeudeker
After putting results in a jupyter notebook, numerical displacement is <0.5% relative error after only 30k steps; this seems pretty good to me. If you're ok with the all of the above changes, I can push the updates into your branch whenever!

[jgiven100]

Just pushed updates with 3d model & matched the existing naming convention for the 2d model. Both 2D and 3D benchmarks are the 1D column