Lighter Than Air Dynamics Systems #2241

henrykotze · 2023-11-11T14:34:55Z

🎉 New feature

Summary

This adds the dynamics to simulate a lighter-than-air vehicle such as blimps/airships. The modelling is based on [1] and [2]. Previously we added an airship-dynamics-plugin to Gazebo-Classic for PX4 Gazebo SITL , but we suffered simulation instability similar to that of the underwater-vehicles since Gazebo-Classic could not simulate the Added Mass dynamics.

This PR brings that airship-dynamics-plugin to Gazebo which supports the Added Mass dynamics.

Furthermore, I have extended, the Link class to provide access to the AddedMassMatrix, to allow the lighter-than-air system to easily access this matrix.

The code is somewhat based of the Hydrodynamics system.

I have an STL file which I can contribute, which is an envelope from Wind Reiter, and the coefficients in the integrations test is for this envelope model.

Citations

[1] Li, Y., & Nahon, M. (2007). Modeling and simulation of airship dynamics. Journal of Guidance, Control, and Dynamics, 30(6), 1691–1700.
[2] Li, Y., Nahon, M., & Sharf, I. (2011). Airship dynamics modeling: A literature review. Progress in Aerospace Sciences, 47(3), 217–239.

Test it

I have written a small integration test to check whether the lighter-than-air system is loaded correctly and stable.

Checklist

Signed all commits for DCO
Added tests
Added example and/or tutorial
Updated documentation (as needed)
Updated migration guide (as needed)
Consider updating Python bindings (if the library has them)
codecheck passed (See contributing)
All tests passed (See test coverage)
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henrykotze · 2023-11-11T14:47:08Z

Hi, I tried to get this PR as ready as possible for merging (reading the contribution docs and implementing the requirements), and have reached an unproductive state where I need some feedback to take this forward. So any comments, and or further requirements to implement would help alot.

I am still thinking of more tests to add to ensure any future additions will keep the core dynamics of LTA vehicles unchanged (except if some new modelling arises), since the system is unstable when having a velocity.

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.hh

ahcorde · 2023-11-14T12:05:09Z

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.hh

+                            math::Matrix3d m11, math::Matrix3d m12,
+                            math::Matrix3d m21, math::Matrix3d m22);
+
+    public: math::Vector3d added_mass_force(math::Vector3d lin_vel,


test/integration/lighter_than_air_dynamics.cc

ahcorde · 2023-11-14T12:05:38Z

test/integration/lighter_than_air_dynamics.cc

+ */
+
+#include <gtest/gtest.h>
+


include vector, string

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

arjo129

Apart from @ahcorde's style comments, there are some functionality related things which need minor changes that I've highlighted. Also a file in the examples/ folder would be nice as end users who install binaries don't get the unit tests!

test/worlds/CMakeLists.txt

src/systems/lighter_than_air_dynamics/CMakeLists.txt

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

arjo129 · 2023-11-16T06:24:45Z

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

+  }
+
+  this->dataPtr->airDensity = SdfParamDouble(_sdf, "airDensity",
+                                  SdfParamDouble(_sdf, "air_density", 998)


Just keep air_density.

arjo129 · 2023-11-20T23:42:23Z

Can you fix your commit sign-off. Instructions are here

codecov · 2023-11-21T00:45:31Z

Codecov Report

Attention: Patch coverage is 83.05085% with 30 lines in your changes are missing coverage. Please review.

Project coverage is 64.82%. Comparing base (922eea7) to head (bf74047).
Report is 3 commits behind head on gz-sim7.

❗ Current head bf74047 differs from pull request most recent head 3705ccd. Consider uploading reports for the commit 3705ccd to get more accurate results

Files	Patch %	Lines
...ighter_than_air_dynamics/LighterThanAirDynamics.cc	83.04%	29 Missing ⚠️
src/Link.cc	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           gz-sim7    #2241      +/-   ##
===========================================
- Coverage    64.88%   64.82%   -0.06%     
===========================================
  Files          360      358       -2     
  Lines        29448    29337     -111     
===========================================
- Hits         19108    19019      -89     
+ Misses       10340    10318      -22

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

henrykotze · 2023-11-22T05:20:37Z

I hope its okay that I squashed and force pushed, I didnt intent to remove the co-author commits, but rather keep the history much more clearer.

arjo129 · 2023-11-22T06:37:56Z

I hope its okay that I squashed and force pushed, I didnt intent to remove the co-author commits, but rather keep the history much more clearer.

No worries. You have to force push for DCO so 🤷

henrykotze · 2023-11-27T14:42:15Z

Somehow missed all the other style suggestions.
Let me know if there is anything else to do here.

henrykotze · 2023-12-05T05:21:43Z

Anything else todo here?

arjo129 · 2023-12-27T03:09:10Z

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

+                                                      -visc_normal_y_);
+
+  // Added Mass forces & Torques
+  auto force_added_mass = -1.0 * this->added_mass_force(linear_vel,


IIUC, if you use the SDF <fluid_added_mass> tags, the added mass gets added by the physics engine. Theres no need to add the added mass terms here. I think @azeey, @mabelzhang or @quarkytale may be able to elaborate more on that.

The tag is <fluid_added_mass>, but yes. See https://github.com/gazebosim/gz-physics/blob/d1a76c00f3247ca11e87680d4a349ac68f4df52b/dartsim/src/SDFFeatures.cc#L707
and https://github.com/gazebosim/gz-physics/blob/32bef6dc3a24937004789fd768cf548c2c89d6ab/dartsim/src/AddedMassFeatures.cc#L24

Thanks for this!

Referring to the paper, on which I have based the dynamics, the added mass effects should be incorporated in two places: (1) In the linear body acceleration and angular body acceleration, and then (2) in the coupling of the linear and angular velocities. I have added picture from the paper.

From my understanding, the physics engine incorporates it into the former (the acceleration terms). I have just added the forces and torques which is created by the added mass due to the coupling of the linear and angular velocities. I hope this make sense.

Equation 1

Would be awesome if someone could provide insight into the backend of the physics engine and how it incorporate the added mass effects. From my understanding, it would only compute the first term in equation (6) and not both terms.

Yep! You are right. The physics engine will only include added mass in the acceleration term. Any interaction due to velocities would have to be done outside of the engine.

arjo129 · 2023-12-27T03:10:33Z

examples/worlds/lighter_than_air_blimp.sdf

+    <gravity>0 0 -9.81</gravity>
+
+    <plugin
+      filename="ignition-gazebo-physics-system"


For forward compatibility use gz-sim-physics-system instead.

azeey · 2024-01-02T18:55:20Z

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

+  auto pose = baseLink.WorldPose(_ecm);
+  // Since we are transforming angular and linear velocity we only care about
+  // rotation. Also this is where we apply the effects of current to the link
+  auto linear_vel = pose->Rot().Inverse() * (linearVelocity->Data());


please use camelCase for all variable names. See https://gazebosim.org/docs/harmonic/contributing#style-guides

Will do!

I see there isnt really a style requirement for function parameters. Should I make my function parameters also camelCase?

All variable names and function names use camelCase

azeey · 2024-01-02T19:03:41Z

src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.cc

+                                                      -visc_normal_y_);
+
+  // Added Mass forces & Torques
+  auto force_added_mass = -1.0 * this->added_mass_force(linear_vel,


The tag is <fluid_added_mass>, but yes. See https://github.com/gazebosim/gz-physics/blob/d1a76c00f3247ca11e87680d4a349ac68f4df52b/dartsim/src/SDFFeatures.cc#L707
and https://github.com/gazebosim/gz-physics/blob/32bef6dc3a24937004789fd768cf548c2c89d6ab/dartsim/src/AddedMassFeatures.cc#L24

arjo129

Sorry for the long feedback time. The plugin itself looks good to me. However the test does not seem to check for any velocity/positon values. This means we may not be able to catch regressions.

arjo129 · 2024-03-19T03:34:34Z

test/integration/lighter_than_air_dynamics.cc

+  EXPECT_EQ(2000u, bodyVels.size());
+
+  EXPECT_NE(model.Entity(), kNullEntity);
+  EXPECT_NE(body.Entity(), kNullEntity);


Sorry for the incredibly long feedback time. But this test does not seem to be checking anything about the behaviour of the dynamics. It'll be hard to spot regressions if we dont test that.

I agree that the tests are limited which I have implemented.
Will have a look at this more closely!
Thanks for the feedback.

What we do for hydrodynamics is push a model and then try to measure its terminal velocity. Perhaps this is an approach which you want to adopt?

Added tests to check the instability of pitch and yaw.

arjo129

Thanks for iterating on this PR. LGTM!

henrykotze · 2024-05-14T07:18:25Z

Thanks for iterating on this PR. LGTM!

Thank you for your review and follow ups! Its much appreciated!

Review is stale

arjo129 · 2024-05-14T07:35:44Z

Can you try merging the base branch once it seems the ABI checker is not happy.

henrykotze · 2024-05-14T07:55:50Z

Rebased on top of gz-sim7?

arjo129 · 2024-05-14T07:58:39Z

Yep.

copy of Hydrodynamics folder, and rename to lta Renamed to LighterThanAirDynamics - Added some initial private data - Requires still alot of cleanup some initial dynamics added Building sucessfully with some warnings Running test to determine succesfull Spawning successfull ran tests, but still debugging alot Added additional debug messages Protection for zero division - Test running sucessfully with adding forces and torques, but requires more extensive testing and validation Improved Documentation,some more work on tests Improve documentation to include math Silver bullet model withs its coefficients small documentation update Code style updates. wip Style checks completed Small correction to dynamics Added Mass Force and Torques included - Link class now provides the FluidAddedMassMatrix Removed Munk from added mass & correct coeff names Signed-off-by: henrykotze <henry@flycloudline.com> update year Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> update format suggestion Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> update format suggestion in added_mass_force Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> format fix: function header Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> update formatting Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> Update src/systems/lighter_than_air_dynamics/LighterThanAirDynamics.hh Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> update year Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> Functionality updates and style updates Signed-off-by: henrykotze <henry@flycloudline.com> Example added for Lighter-than-air envelope Signed-off-by: henrykotze <henry@flycloudline.com> Use numerical limits to query precision of types Signed-off-by: henrykotze <henry@flycloudline.com> fix integration path for sdf file Signed-off-by: henrykotze <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> update year Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> style format update Co-authored-by: Alejandro Hernández Cordero <ahcorde@gmail.com> Signed-off-by: Henry Kotzé <henry@flycloudline.com> remove commented wind component Signed-off-by: henrykotze <henry@flycloudline.com> fix whitespace error from pre-commit Signed-off-by: henrykotze <henry@flycloudline.com> codecheck fix conform to style guide requirements wip: test with forces acting on it working tests implementing, cleanup required cleanup and formatting revert back to original example more revert to original

henrykotze requested a review from mjcarroll as a code owner November 11, 2023 14:34

github-actions bot added the 🌱 garden Ignition Garden label Nov 11, 2023

henrykotze force-pushed the lighter-than-air-dynamic branch from 10a6d18 to 9e6800d Compare November 13, 2023 10:45

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henrykotze force-pushed the lighter-than-air-dynamic branch 2 times, most recently from 4c468db to bfd3d26 Compare December 6, 2023 14:38

arjo129 reviewed Dec 27, 2023

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henrykotze force-pushed the lighter-than-air-dynamic branch from bfd3d26 to bf74047 Compare February 13, 2024 15:58

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henrykotze force-pushed the lighter-than-air-dynamic branch from 07207f9 to 3705ccd Compare May 14, 2024 08:02

arjo129 enabled auto-merge (squash) May 14, 2024 09:10

arjo129 merged commit 4019e09 into gazebosim:gz-sim7 May 14, 2024
8 of 9 checks passed

		*/

		#include <gtest/gtest.h>

Lighter Than Air Dynamics Systems #2241

Lighter Than Air Dynamics Systems #2241

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henrykotze commented Nov 11, 2023 • edited

🎉 New feature

Summary

Citations

Test it

Checklist

henrykotze commented Nov 11, 2023

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arjo129 commented Nov 20, 2023 • edited

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Codecov Report

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henrykotze commented May 14, 2024

arjo129 commented May 14, 2024

henrykotze commented May 14, 2024

arjo129 commented May 14, 2024

henrykotze commented Nov 11, 2023 •

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