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Introduce trilinear flex parametrization.

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These flexes use only 24 DOFs (3 per vertex of the bounding box), while colliding with the full high resolution mesh.

On an 8x8x8 cube, the performance using DOFs at all vertices is

```
 Simulation time      : 18.74 s
 Steps per second     : 533
 Realtime factor      : 0.53 x
 Time per step        : 1874.4 µs

 Contacts per step    : 114.88
 Constraints per step : 3322.51
 Degrees of freedom   : 1536
```

With the new implementation, it is the following:

```
 Simulation time      : 1.82 s
 Steps per second     : 5507
 Realtime factor      : 5.51 x
 Time per step        : 181.6 µs

 Contacts per step    : 38.84
 Constraints per step : 155.36
 Degrees of freedom   : 24
```

PiperOrigin-RevId: 721008829
Change-Id: I833df027527db578d86667cc4b24295bcf6f7d22
This commit is contained in:
Alessio Quaglino
2025-01-29 09:37:37 -08:00
committed by Copybara-Service
parent 1a4b821b6b
commit 7cdf180641
47 changed files with 8967 additions and 96 deletions
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doc/modeling.rst
+2 -12
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@@ -1335,9 +1335,7 @@ improved realism and accuracy. The edge-based model could be seen as a "lumped"
coupling of deformation modes (e.g. shear and volumetric) is averaged in a single quantity. The continuum model enables
instead to specify shear and volumetic stiffnesses separately using the `Poisson's ratio
<https://en.wikipedia.org/wiki/Poisson%27s_ratio>`__ of the material. For more details, see the `Saint Venant-Kirchhoff
<https://en.wikipedia.org/wiki/Hyperelastic_material#Saint_Venant%E2%80%93Kirchhoff_model>`__ hyperelastic model. This
functionality is currently based on first-party :ref:`engine plugins<exPlugin>` as of MuJoCo 3.0 but may be integrated
into the engine in future releases.
<https://en.wikipedia.org/wiki/Hyperelastic_material#Saint_Venant%E2%80%93Kirchhoff_model>`__ hyperelastic model.
**Creation and visualization**.
@@ -1345,20 +1343,12 @@ into the engine in future releases.
<option timestep=".001"/>
<extension>
<plugin plugin="mujoco.elasticity.solid"/>
</extension>
<worldbody>
<flexcomp type="grid" count="24 4 4" spacing=".1 .1 .1" pos=".1 0 1.5"
radius=".0" rgba="0 .7 .7 1" name="softbody" dim="3" mass="7">
<contact condim="3" solref="0.01 1" solimp=".95 .99 .0001" selfcollide="none"/>
<edge damping="1"/>
<plugin plugin="mujoco.elasticity.solid">
<config key="poisson" value="0.2"/>
<!--Units are in Pa (SI)-->
<config key="young" value="5e4"/>
</plugin>
<elasticity poisson="0.2" young="5e4">
</flexcomp>
</worldbody>