Manufacturing and control of autonomous underwater vehicle

• Main Author: Ang, Elijah Hao Wei
• Other Authors: Basman Elhadidi
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering::Control engineering; DRNTU::Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/78587
• Institution: Nanyang Technological University

A hover style autonomous underwater vehicle (AUV) was designed in this thesis. 8 thrusters were employed in this design to allow for control over all 6 degrees of freedom. A streamlined outer shell was designed to encapsulate the AUV such that the outer profile of the vehicle is streamlined, reducing the pressure drag on the AUV. Fossen's model was used for the mathematical modelling of the AUV. Since the AUV designed has 3 planes of symmetry, off-diagonal terms of the hydrodynamic matrices can be neglected. This makes calculating the hydrodynamic coefficients easier. These coefficients were calculated using computational fluid dynamics simulations, and were used in the mathematical modelling of the AUV. The open loop response of the AUV was examined by giving it a step input for each of the 6 degrees of freedom. Surge, sway, heave and yaw exhibits first order responses, while roll and pitch exhibits second order responses. A PID controller was implemented, and the close loop response was examined, and all the degrees of freedoms' responses behaved well. A trajectory analysis was done to determine a more efficient method to move from a point to another. Results showed that coupling pitching with surging motion is 50% more efficient in time, and 22% more efficient in energy when compared to discrete translational motions. An inertial navigation system (INS) and inertial measurement unit (IMU) were compared for their performance. The INS outperform the IMU with cleaner and more stable data. However, both were not suitable for measuring displacements, and thus, additional sensors are required. The AUV was not able to undergo water experiments as some hardware were damaged due to the poor implementation of the start-stop switch, which caused a short circuit in the system.