Implement multi-cell finite element method for interpolated flexes.

This change introduces a `flex_cellcount` field to `mjModel` to specify the number of cells in each dimension for interpolated flexes. The stiffness computation, passive force calculation, and Jacobian derivatives are updated to operate on a per-cell basis, significantly improving performance by localizing computations to the nodes within each cell. PiperOrigin-RevId: 901216393 Change-Id: Ic23132e609de11e71bb7fef8d1f139daad2ec264
2026-04-17 04:10:54 -07:00
parent 8415dff307
commit 6c7ed66781
36 changed files with 1777 additions and 1039 deletions
@@ -0,0 +1,42 @@
+<!-- Copyright 2024 DeepMind Technologies Limited
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<mujoco model="Trilinear">
+  <include file="scene.xml"/>
+
+  <option solver="CG" tolerance="1e-6" timestep=".001" integrator="Euler"/>
+
+  <size memory="100M"/>
+
+  <visual>
+    <map stiffness="100"/>
+  </visual>
+
+  <worldbody>
+    <body>
+      <joint name="press" type="slide" axis="0 0 1" damping="500"/>
+      <geom type="box" size=".02 .2 .2" pos="0 0 .5"/>
+    </body>
+    <flexcomp type="mesh" file="bunny.obj" pos="0 0 0" dim="2" euler="90 0 0" cellcount="3 3 3"
+              radius=".001" rgba="0 .7 .7 1" mass=".05" name="softbody" dof="trilinear">
+      <elasticity young="1e3" poisson="0.1" damping="0.01" elastic2d="stretch"/>
+      <contact selfcollide="none" internal="false"/>
+    </flexcomp>
+  </worldbody>
+
+  <actuator>
+    <position name="press" joint="press" gear="-1 0 0 0 0 0" ctrlrange="-1 1" kp="1000"/>
+  </actuator>
+</mujoco>