The hydrodynamic optimization of a cable-flying vehicle

Profiling the water column with high vertical and horizontal resolution in the deep ocean from a moving vessel is difficult with the current tools. Thus, a new wire-flying vehicle capable of higher resolution, called the WiFly, is being designed. The WiFly will profile the water column as it traverses up and down a ship-towed cable. Wings protruding from the sides of the vehicle body generate vertical lift which will propel it through the water. A control algorithm will alter the angle of attack of the wings and allow the vehicle to travel over a range of speeds and operational depths. The goal of this thesis was to perform a design evaluation of the WiFly vehicle to optimize its profiling performance. The design was optimized by maximizing the potential wing lift and minimizing the vehicle drag in the direction of the most common incident flow angles while maintaining manufacturability and practical size constraints. The vehicle’s performance was measured by evaluating its feasible glide slopes (GSs) which are defined by the ratio of vertical to horizontal velocity along the cable. The project was broken into three sections. First, the velocity and angle of common incident flows on the vehicle were determined through Simulink modeling. Second, the body and wings of the vehicle were designed to house all of the necessary components using computer aided design (CAD) and assessed in FlowSimulation for drag forces. Finally, the vehicle was evaluated in a performance simulation via its GSs. The second and third steps were iterated until an optimum vehicle design was reached. The vehicle was numerically represented in the performance simulation by a set of parameters including the vehicle’s drag coefficients and projected cross-sectional areas. These parameters changed respective to the incident flow angle, surface area of the wings, various wing lift-to-drag ratios (LDRs), and the wings’ lift coefficient. The simulated drag and lift coefficients for both the body and wings were generated using FlowSimulation. By iterating between the performance simulation of the vehicle and its design, the vehicle’s design could be refined. The final body design of the vehicle had the profile of a National Advisory Committee for Aeronautics (NACA) 0025, with a bulbous top and a curved trailing edge. It was approximately 0.9m in height, 1.5m in length, and 0.25m in width. The drag coefficients ranged from 0.023 to 0.085, over the range of incident flow angles. The wings were designed using a modified NACA 0018 profile with an aspect ratio of 3 and a combined lifting surface area of approximately 0.2m2. The wing measured approximately 56cm in span and 20cm at the root chord. The combination of the final body and wing design produced GSs from 3.75 to 5.2 between cable angles of 0 and 30 degrees. Glide slopes of this magnitude are significantly higher than the current water profiling tools as well as the initial goal of 1.0 for this project. This will lead to drastically improved efficiency in ocean water column profiling