Explicit Dynamics may be used for a wide range of applications, and a default set of Analysis Settings designed to provide the most robust solution are not necessarily suited to every application. Therefore, the Type setting allows the selection of particular defaults depending on the requirements of the solution. The following options are available:
Program Controlled – This is the default setting with a priority for a robust solution.
Low Velocity – Recommended for low deformation/velocity (<100m/s) analyses.
High Velocity – Recommended for high deformation/velocity (>100m/s) analyses.
Efficiency – Settings for minimum runtime. In some cases, this may have an effect on robustness and accuracy.
Quasi-static – Recommended for quasi-static analyses.
Drop Test – Recommended for drop test analyses.
The exact Analysis Settings values for each of the Analysis Settings Preference Types are shown in the table below. Switching the Type property will update all of the items displayed in the table as indicated. If any of these settings are subsequently changed, then the Type will be indicated as Custom.
| Program Controlled | Efficiency | Low Velocity | High Velocity | Quasi-Static | Drop Test | ||
|---|---|---|---|---|---|---|---|
| Default (Robustness) | Setting for minimum run time (also minimum robustness and accuracy in some cases) | Recommended setting for low deformation/velocity simulations (<100m/s) | Recommended for high deformation/velocity simulations (>100m/s) | Recommended setting for quasi-static simulations | Recommended setting for drop test analyses | ||
| Analysis Settings | Notes | ||||||
| Step Controls | |||||||
| Timestep Safety Factor | 0.9 | 1 | 0.9 | 0.9 | 0.9 | 0.9 | If solving in the Euler reference frame the maximum timestep safety factor is 0.66667. This will override any values entered by the user. |
| Mass Scaling | No | Yes | Yes | No | Yes | No | You need to enter a reasonable desired timestep. |
| Mass Scaling: Minimum CFL timestep | Off | User Must Define | User Must Define | Off | User Must Define | Off | You need to enter a sensible desired timestep and ensure the physical response is not significantly altered by the additional mass added. |
| Mass Scaling: Maximum Element Scaling Factor (%) | Off | 1000 | 100 | Off | 1000 | Off | |
| Mass Scaling: Maximum Part Scaling | Off | 1000 | 5 | Off | 1000 | Off | |
| Mass Scaling: Update Frequency | Off | 0 | 0 | Off | 0 | Off | Note that for low deformation problems, setting an update frequency of approximately 250 may also help maintain a higher timestep |
| Characteristic Dimension | Diagonals | Opposing Faces | Opposing Faces | Diagonals | Opposing Faces | Opposing Faces | |
| Solver Controls | |||||||
| Beam Time Step Safety Factor | 0.5 | 1 | 0.1 | 0.1 | 0.1 | 0.1 | Increasing the safety factor can lead to unstable results. Check results carefully. |
| Hex Integration Type | Exact | 1pt Gauss | 1pt Gauss | Exact | 1pt Gauss | 1pt Gauss | |
| Shell Sublayers | 3 | 2 | 3 | 3 | 3 | 3 | |
| Shell Inertia Update | Recompute | Rotate | Recompute | Recompute | Recompute | Recompute | Rotate option is most efficient but can lead to unstable results. Check results carefully. |
| Tet Integration | ANP | SCP | NBS | ANP | NBS | NBS | SCP tet is very efficient but suffers from shear and volume locking. Check results carefully if using this option. |
| Minimum Strain Rate Cutoff | 1e-10 | 1e-10 | 0.0 | 1e-10 | 0.0 | 0.0 | |
| Damping Controls | |||||||
| Hourglass Damping | AUTODYN standard | AUTODYN standard | Flanagan Belytschko | AUTODYN standard | Flanagan Belytschko | Flanagan Belytschko | Autodyn standard is not rigid body rotation invariant. Must use Flanagan Belytschko if large rotations are involved. |
| Static Damping | 0 | 0 | 0 | 0 | User Must Define | 0 | For quasi-static analyses, it is recommended that static damping is used, but the value used depends on the configuration of the model. See Explicit Dynamics Damping Controls for more details on selecting an appropriate value. |
| Erosion Controls | |||||||
| On Geometric Strain Limit | Yes | No | No | Yes | No | No | If you expect large deformations and mesh distortions during the simulation, a geometric strain limit of 1.0 to 1.5 will be required for the minimum run time case. |
| Geometric Strain Limit | 1.5 | 0.75 | Unchanged | 1.5 | Unchanged | Unchanged | |
| Output Controls | |||||||
| Save Results on: Equally Spaced Points | 20 | 20 | 50 | 50 | 10 | 50 | |
| Save Result Tracker Data: Cycles | 1 | 10 | 10 | 1 | 10 | 10 | |
| Save Solution Output: Cycles | 100 | 1000 | 100 | 100 | 100 | 100 | |
| Body Interactions: Details options | |||||||
| Nodal Shell Thickness | No | No | No | No | No | No | |
| Body Self Contact | Yes | No | No | Yes | No | No | |
| Element Self Contact | Yes | No | No | Yes | No | No |
When using the Explicit Dynamics analysis system, the Body Self Contact and Element Self Contact settings in the Body Interactions object Details panel should be set to Program Controlled in order for the Analysis Settings Preference Type to have an effect on the Body Interactions objects. If the Program Controlled setting is used, the values of the Body Interactions settings will be as shown in the table.
Note: Consider the following guidelines for setting up other areas of your analysis:
Material Properties
Use simplest Material definition possible
Use Linear Elastic properties unless you need to model non-linearities
Bonds
Only use breakable bonds if you really need to
Meshing
Mesh quality is a critical aspect for model performance and accuracy:
Use Hex Meshes whenever possible
Use the patch independent tetrahedral mesh method to ensure uniform element size and timestep optimization
Avoid small elements unless you need them