boat-simulator

This repository contains MATLAB scripts and Simulink models for the purpose of creating a low-level controller for UBC Sailbot. The model is based on Modeling and Nonlinear Heading Control of Sailing Yachts by Jerome Jouffroy. The pdf can be found here.

Quick Start Instructions

1. Install MATLAB and Simulink. The installer will ask you what toolboxes you want to install and be sure to install the ROS Toolbox. This is free for UBC students, with instructions here

2. Clone the repository git clone https://github.com/UBCSailbot/boat-simulator.git

3. Open MATLAB and change your working directory to the boat-simulator folder that you just cloned

you can now run relevant Simulink files. To run the boat simulator as a standalone ROS node, complete the following:

4. Install ROS Melodic on a Ubuntu 18.04 (or similar). http://wiki.ros.org/ROS/Tutorials/InstallingandConfiguringROSEnvironment

5. Find the location that you want to create a ROS workspace (eg. cd ~)

6. Type the commands mkdir -p catkin_ws/src cd catkin_ws catkin_make.

7. Clone the sailbot-msgs repository in the src folder: git clone https://github.com/UBCSailbot/sailbot-msg.git.

8. update the add_custom_ros_msg.m file and run it. Follow MATLAB's follow up promots as well

9. run boat_simulator_ros_node.slx which subscribes to the /rudder_winch_actuation_angle topic and publishes to the /sensors topic. See this confluence page for more details.

Variables

There are many variables in this complicated model. While the Jouffroy paper does a good job explaining the varibles, it is long and overwhelming to read and understand. Here, I will define the variables more clearly and highlight some easy misunderstandings (as of Aug 2019):

• Two notable coordiate frames:

  • n-frame - world frame with xyz = North-East-Down

  • b-frame - boat frame with xyz = Forward-Right-Down

• n = [x;y;phi;psi]

  • x - position in n-frame

  • y - position in n-frame

  • phi - angle around x-axis in n-frame

  • psi - angle around z-axis in n-frame

• vss = [surge;sway;roll;yaw]

  • surge - linear velocity forward in b-frame (u in paper)

  • sway - linear velocity right in b-frame (v in paper)

  • roll - angular velocity around x-axis in b-frame (p in paper)

  • yaw - angular velocity around z-axis in b-frame (r in paper)

• n_dot, v_dot - time derivatives of above variables

All of the following variables are vectors with 4 components, with the components directions matching vss above. This means component 1 is forward, 2 is right, 3 is angular around forward-axis, 4 is angular around down-axis.

• T - vector of propulsive forces (from rudder and sail)

• D - vector of damping forces

• g - vector of righting moments

All of the following are parameters that must be tuned/tested (not exhaustive list)

• (x_r, y_r, z_r) - Center of effort rudder

  • change r to s for sail, k for keel, h for hull

The following are functions that are complete approximations, might need some input from professors to see if valid

• lift = 0.5*rho*A*(v^2)*k1*\sin(2*alpha)

• drag = 0.5*rho*A*(v^2)*k1*(1-cos(2*alpha))

• F_rh = v_ah^2