A PRESCRIBED FLIGHT PERFORMANCE ASSESSMENT FOR UNDERSEA VEHICLE AUTOPILOT ROBUSTNESS

Open Access
Author:
Bowman, Daniel Joseph
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 09, 2016
Committee Members:
  • Dr. A. Scott Lewis, Thesis Advisor
  • Dr. Sean Brennan, Committee Member
  • Dr. Karen Thole, Committee Member
Keywords:
  • Undersea Vehicle
  • Autopilot Robustness
  • Flight Performance
  • Weight Configuration
  • Trim
Abstract:
Undersea vehicles are widely used in commercial and military applications to explore the open sea around the world. However, the modification of an existing design of an undersea vehicle for a specific application can be an intimidating task without a prescribed design assessment. Furthermore, operational use of a large class of the highly utilized axisymmetric undersea vehicle design sometimes requires unplanned and unforeseen mission payload weight and mass distribution changes. This research aims to provide the vehicle designer with a platform that enables faster implementation of confident design changes from an assessment while suppressing the level of uncertainty in resulting undersea vehicle flight performance and maneuverability. Unlike the narrow focus of many current undersea vehicle design assessments, this research simultaneously evaluates the broader impacts and benefits of changeability to common mechanical system design parameters and autopilot design. Two non-dimensional parameters that encompass the common changes to undersea vehicle weight configurations are defined. Additionally, the robustness of a well-tuned fixed weight configuration autopilot for an undersea vehicle is assessed against perturbed vehicle weight configuration models. Results are presented through evaluations of steady level flight, steady turn, and steady depth change flight performance simulations. The results suggest that a baseline autopilot is robust to changes in weight configuration but at the cost of steady state depth errors. The observed steady state depth errors are an outcome of the new trim characteristics of the perturbed weight configuration vehicle for which the baseline autopilot was not designed to accommodate. However, an offset compensation on the depth command to the autopilot enables the vehicle to attain desired depths. Ultimately, for a known typical range of unforeseen changes to an undersea vehicle’s weight configuration a baseline autopilot can be very robust with the addition of offset compensations on the depth commands.