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Glider Control System Simulation

Intro

This program simulates the physics of an underwater glider, including drag, buoyancy, and lift. It also simulates a control system for the glider.

Background

I wrote this program for UVEEC, a club at the University of Victoria. The club's current project is to design and build an underwater glider to be deployed in Saanich Inlet to collect data. As one of the club's software team leads, my job is to design the control system. Part of that control system is designed to control the depth and movement of the glider. The control system for the Glider must be tuned. This is a long process that, if done entirely in Saanich Inlet with an assembled Glider, would take a long time and involve risk of losing the Glider.

Purpose

The control system can be simulated using this program, allowing for preliminary tuning parameters to be found.

Running

  1. Create a config file, an example is provided (config.json)

  2. Run the program with python3 GliderCsSim.py

The program with show two plots, one is the glider's x - y position with time.

The second has 3 plots, the top is the roll, pitch, and yaw of the glider over time (in degrees, this is the only time degrees are used). Middle is the glider's depth, vertical speed, and vertical acceleration. Bottom is the control system's logging.

TODO

  1. Add sensors with noise that feed the control system

  2. Redesign the control system to work better

Future Plans

  1. ROS 2 integration so parts of the Glider's actual CS may be tested.

Config Options

All units are metric base units, e.g. meters for length, seconds for time, radians for angles, kilograms for mass.

glider

control_system

pid parameters should be mostly self explanatory

high_depth

The depth the control system will target when surfacing

low_depth

The depth targeted when diving

frequency

How many times per second the control system updates

The more it runs the slower the simulation

hull

The hull is a capsule shape (cylinder with hemispheres at the end)

length

Length of the cylinder part, total length of the glider would be length + 2 * radius

radius

Radius of the cylinder and end caps

drag_multiplier

This is kind of just to simulate different conditions, drag coefficients are calculated based on length and radius, and can't be set.

The hull's position is (0, 0, 0)

buoyancy_engine

This is a tank with a pump. It pumps water in until it's full, or pumps it out until it's empty.

The buoyancy and mass of the glider must be balanced correctly or the glider will be unable to dive or surface. I made this calculator for that purpose.

hydrofoil

It's a fancy name for wing. The coefficient of lift is approximated as a line with slope lift_curve_slope until stall_angle, where it becomes a line to zero lift at 45 degrees.

initial_position / velocity / acceleration

Positive x is forward

Positive y is right

Positive z is up

initial_orientation / angular_velocity / angular_acceleration

Positive x is roll right

Positive y is pitch up

Positive z is yaw right

sim

timestep

How much time passes between physics calculations, lower is more accurate but slower.

end_time

How much time is simulated. More time takes longer.

The simulation runs until the end_time is reached, there is no limit to how many iterations there are. The number of iterations is end_time / timestep.

Written by Anthony Cieri - email