Remove cloth and rope composites and deprecate loop.

PiperOrigin-RevId: 568168329
Change-Id: Ida4a5236bef74828c7bf59affdc28adea3db53b1

model/plugin/elasticity/flag.xml

@@ -0,0 +1,55 @@
+<!-- Copyright 2021 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="Flag">
+<!-- Degree of Freedom (nv):  340
+     Tendons (ntendon):       288
+     Actuators (nu):          0
+     Constraints (nefc):      0
+     This model of a flag passively flapping in the wind has no constraints and is designed to
+     exert smooth dynamics computations.
+-->
+  <statistic center=".4 0 .8" extent="1.3"/>
+
+  <option wind="5 5 0" density="10" solver="CG" tolerance="1e-6">
+  </option>
+
+  <extension>
+    <plugin plugin="mujoco.elasticity.shell"/>
+  </extension>
+
+  <worldbody>
+    <geom name="floor" type="plane" size="0 0 .1"/>
+    <light diffuse=".6 .6 .6" specular="0.2 0.2 0.2" pos="0 0 4" dir="0 0 -1"/>
+    <body pos="0 0 1">
+      <composite type="particle" count="9 19 1" spacing="0.05" flatinertia="0.01">
+        <skin texcoord="true" inflate="0.005" subgrid="4"/>
+        <geom type="ellipsoid" size="0.025 0.01 0.025" rgba=".8 .2 .1 1" group="4"/>
+        <plugin plugin="mujoco.elasticity.shell">
+          <config key="poisson" value="0"/>
+          <config key="damping" value="0.001"/>
+          <config key="thickness" value="1e-2"/>
+          <!--Units are in Pa (SI)-->
+          <config key="young" value="3e6"/>
+        </plugin>
+      </composite>
+    </body>
+  </worldbody>
+
+  <equality>
+    <connect body1="B0_0_0" anchor="0 0 0" solref="0.0002 1"/>
+  </equality>
+</mujoco>
+

model/plugin/elasticity/plate.xml

@@ -41,7 +41,7 @@
     <composite type="particle" count="16 16 1" spacing="0.05" offset="0 0 1">
       <geom size=".02" rgba=".8 .2 .1 1" group="4" density="1000"
             condim="3" solref="0.01 1" solimp=".95 .99 .0001"/>
-      <skin inflate="0.01" rgba=".4 0 .3 1" subgrid="4"/>
+      <skin inflate="0.0001" rgba=".4 0 .3 1" subgrid="1"/>
       <plugin plugin="mujoco.elasticity.shell">
         <config key="poisson" value="0"/>
         <config key="damping" value="0.001"/>