Buoyancy improvements

[arjo129]

🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸🔸

🎉 New feature

Depends on gazebosim/gz-math#219.

Summary

Often when simulating a maritime environment one may need to simulate both
surface and underwater vessels. This means the buoyancy plugin needs to
take into account two different fluids. One being water with a density of
1000kgm^-3 and another being air with a very light density of say 1kgm^-3.
An example for such a configuration may be found in the graded_buoyancy.sdf world.

ign gazebo -v 4 graded_buoyancy.sdf

You should be able to see a sphere bobbing up and down undergoing simple
harmonic motion on the surface of the fluid (this is expected behaviour
as the SHM is usually damped by the hydrodynamic forces. See the hydro-
dynamics plugin for an example of how to use it). The key part of this is

<graded_buoyancy>
   <default_density>1000</default_density>
   <density_change>
     <above_depth>0</above_depth>
     <density>1</density>
  </density_change>
</graded_buoyancy>

The default density tag says that by default the world has a fluid density
of 1000kgm^-3. This essentially states that by default the world is filled
with dihydrogen monoxide (aka water). The <density_change> tag
essentially establishes the fact that there is a nother fluid. The
<above_depth> tag says that above z=0 there is another fluid with a
different density. The density of that fluid is defined by the <density>
tag. We will be simulating air with a fluid density of 1kgm^-3.

Test it

TODO

• Write write unit tests.
• Update other examples (possibly in another PR).

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[chapulina]

I know this is still WIP, but I just did a quick pass

[chapulina]

Works for me! I pushed a new example and a small fix for it on 2abcabd. Now we just need to merge and release the ign-math PR.

[codecov]

Codecov Report

Merging #818 (7c3dd55) into main (4be711c) will increase coverage by 0.09%.
The diff coverage is 86.79%.

❗ Current head 7c3dd55 differs from pull request most recent head f6ce49f. Consider uploading reports for the commit f6ce49f to get more accurate results

@@            Coverage Diff             @@
##             main     #818      +/-   ##
==========================================
+ Coverage   63.47%   63.56%   +0.09%     
==========================================
  Files         241      241              
  Lines       19577    19675      +98     
==========================================
+ Hits        12426    12507      +81     
- Misses       7151     7168      +17     

Impacted Files	Coverage Δ
src/systems/buoyancy/Buoyancy.hh	100.00% <ø> (ø)
src/systems/buoyancy/Buoyancy.cc	82.35% <86.79%> (+7.07%)	⬆️
src/gui/plugins/plot_3d/Plot3D.cc	43.47% <0.00%> (-4.35%)	⬇️
src/EntityComponentManager.cc	84.83% <0.00%> (+0.15%)	⬆️

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