Dynamic modeling of a simple pendulum underwater

A ros2 package for dynamic modeling of a simple pendulum fully immersed underwater with rviz visualization

Forces diagram

Dynamic modeling

For more details about the modeling, kindly see this report.

ros2 program archeticutre

Installation

Before you install the package, make sure that you have the joint state publisher and xacro packeges installed on your ros2 system by typing the following:

sudo apt install ros-<ros2-distro>-joint-state-publisher

sudo apt install ros-<ros2-distro>-xacro

After that, navigate to your ros2 workspace folder and then to the src folder by running this command:

cd ~/<YOUR ROS2 WORKSPACE>/src

Then, run this command:

git clone https://github.com/Elkholy2021/pendulum_simulation.git

Static configuration

To modify the simulation parameters like mass, length, water current, drag, etc .. , kindly open the yaml file in config folder to modify them by running this command:

gedit ~/<YOUR ROS2 WORKSPACE>/src/pendulum_simulation/config/pendulum_params.yaml

Note: make sure to write the parameter values with a decimal point >> e.g. 2.0 not 2

Starting the simulation

To start the simulation, kindly navigate to package directory by running this command:

cd ~/<YOUR ROS2 WORKSPACE>/src/pendulum_simulation

And then run the bash script start_simulation.sh using this command:

./start_simulation.sh

Configuration on the fly

You can also change the water current vector directrly from the terminal without building the package everytime by running the water_current_pub and parsing the water current vector components as ros arguments by typing this command as an example:

ros2 run pendulum_simulation water_current_pub --ros-args -p "x:= 4.1" -p "y:=0.0" -p "z:=-2.1"

Adding disturbances to the water current

Also if you want to add some disturbances to the water current you can add the ros-arg dist which is integer greater than or equal to zero where zero is no disturbances and high number means high fluctions. You can simply run this command as an example:

ros2 run pendulum_simulation water_current_pub --ros-args -p "x:= 4.1" -p "y:=0.0" -p "z:=-2.1" -p "dist:=15"

Note: If you did not provide the arguments, the node will publish the default values

Note: If you did not run the node water_current_pub or the node got inturpted while running, the simulation parameters will be loaded from the yaml file.

References

• Varghese Mathai, Laura A. W. M. Loeffen, Timothy T. K. Chan, and Sander Wildeman. Dynamics of heavy and buoyant underwater pendulums. Journal of Fluid Mechanics, 862:348–363, 2019. doi:10.1017/jfm.2018.867.
• https://automaticaddison.com/how-to-load-a-urdf-file-into-rviz-ros-2/
• https://docs.ros.org/en/foxy/Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Cpp-Publisher-And-Subscriber.html