Introduction

LS-DYNA Implicit Workshop

Problem #11: Ball Pressed Into Plate

Objectives
* Learn when implicit methods can run faster than explicit
methods.
* Learn to troubleshoot contact and convergence problems.

Problem Description
A hemispherical ball of brick elements is displaced into a
plate of brick elements. The plate is supported around its edges.

Input Filename: hemi.k

Procedure
Copy the input file to your local directory. The simulation
is initially set up to run explicitly. Start the job and
estimate how long it will take to finish. Stop the job
using stop when your patience runs thin.

1. How long will the explicit job take to run?

Edit the input deck and activate the implicit method.
Run the simulation and postprocess the results.

2. Does the problem run to completion?

3. What is the meaning of the negative eigenvalue warning message?

Modify the input deck to perform an eigenvalue analysis.
Extract the lowest 30 modes.

4. Are any zero or rigid body modes detected?

5. What was the problem with this model?

6. Why did this model run as an explicit analysis?

Use *BOUNDARY_SPC_SET to add appropriate constraints to the
ball (use the existing node set ID #1.) Repeat the simulation.

7. Examine the contact condition (HINT: cut a section plane
normal to the Y-direction using SPLANE buttons). How deeply
does the ball penetrate the plate?

To reduce penetration, use the penalty scale factor to
increase the contact interface penalty stiffness by 10x
(SLSFAC=1.0 on *CONTROL_CONTACT). Repeat the simulation.

8. How long does the simulation take to run using implicit
method?

Is the penetration problem improved?