Simple restoring moments test for ignition gazebo

buoyancy_restoring_moments_test.sdf

<sdf version="1.6">
  <world name="buoyancy">

    <physics name="1ms" type="ode">
      <max_step_size>0.001</max_step_size>
      <real_time_factor>1</real_time_factor>
    </physics>
    <plugin
      filename="ignition-gazebo-physics-system"
      name="ignition::gazebo::systems::Physics">
    </plugin>
    <plugin
      filename="ignition-gazebo-user-commands-system"
      name="ignition::gazebo::systems::UserCommands">
    </plugin>
    <plugin
      filename="ignition-gazebo-scene-broadcaster-system"
      name="ignition::gazebo::systems::SceneBroadcaster">
    </plugin>
    <plugin
      filename="ignition-gazebo-buoyancy-system"
      name="ignition::gazebo::systems::Buoyancy">
      <uniform_fluid_density>1000</uniform_fluid_density>
      <!--<graded_buoyancy>
        <default_density>1000</default_density>
        <density_change>
          <above_depth>100</above_depth>
          <density>1</density>
        </density_change>
      </graded_buoyancy>-->

    </plugin>

    <light type="directional" name="sun">
      <cast_shadows>true</cast_shadows>
      <pose>0 0 10 0 0 0</pose>
      <diffuse>1 1 1 1</diffuse>
      <specular>0.5 0.5 0.5 1</specular>
      <attenuation>
        <range>1000</range>
        <constant>0.9</constant>
        <linear>0.01</linear>
        <quadratic>0.001</quadratic>
      </attenuation>
      <direction>-0.5 0.1 -0.9</direction>
    </light>

    <model name='submarine'>
      <pose>0 0 0 0.1 0 0</pose>
      <link name='body'>

        <inertial>
          <mass>1000</mass>
          <inertia>
            <ixx>86.28907821859966</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>86.28907821859966</iyy>
            <iyz>0</iyz>
            <izz>5.026548245743671</izz>
          </inertia>
        </inertial>

        <collision name='body_collision'>
          <pose>0 0 -0.08 0 0 0</pose>
          <geometry>
            <box>1 1 1</box>
          </geometry>
        </collision>

        <visual name='body_visual'>
          <geometry>
            <box>
              <size>1 1 1</size>
            </box>
          </geometry>
        </visual>
      </link>
    </model>
  </world>
</sdf>