Thesis (Ph. D.)--Griffith University, 1998. / Includes bibliographical references (leaves 116-134).

Thesis (Master of Engineering in Mechanical Engineering)--Cape Peninsula University of Technology, 2018. / Underwater glider wings are the lifting surfaces of unmanned underwater vehicles UUVs depending on the chosen aerofoil sections. The efficiency as well as the performance of an underwater glider mostly depends on the hydrodynamic characteristics such as lift, drag, lift to drag ratio, etc of the wings. Among other factors, the geometric properties of the glider wing are also crucial to underwater glider performance. This study presents an opportunity for the numerical investigation to improve the hydrodynamic performance by incorporating curvature at the trailing edge of a wing as oppose to the standard straight or sharp trailing edge. A CAD model with straight leading edge and trailing edge was prepared with NACA 0016 using SolidWorks 2017. The operating conditions were setup such that the inlet speed varies from 0.1 to 0.5 m/s representing a Reynolds number 27.8 x 10ᵌ and 53 x 10ᵌ. The static pressure at different angles of attack (AOA) which varies from 2 to 16degrees at the increment of 2degrees for three turbulent models (K-Ԑ-standard, K-Ԑ-RNG and K-Ԑ-Realizable), was computed for upper and lower surfaces of the modified wing model using ANSYS Fluent 18.1. Thereafter the static pressure distribution, lift coefficient, drag coefficient, lift to drag ratio and pressure coefficient for both upper and lower surfaces were analysed. The findings showed that the lift and drag coefficient are influenced by the AOA and the inlet speed. If these parameters change the performance of the underwater glider changes as depicted by figure 5.6 and figure 5.7. The hydrodynamics of the underwater glider wing is optimized using the Cʟ/Cᴅ ratio as function of the operating conditions (AOA and the inlet speed). The investigation showed that the optimal design point of the AOA of 12 degrees and a corresponding inlet speed of 0.26m/s. The critical AOA matched with the optimal design point AOA of 12 degrees. It was also observed that Cp varies across the wing span. The results showed the Cp is higher closer to the fuselage while decreasing towards the mid-span and at the tip of the wing. This showed that the wing experiences more stress close to the fuselage than the rest of the wing span which implies that a higher structural rigidity is required close to the fuselage. The results of the drag and lift curves correspond to the wing characteristics typical observed for this type of aerofoil.

Micro aerial vehicle development and atmospheric flight on Mars are areas that require research in very low Reynolds number flight. Facilities for studying these problems are not widely available. The upper atmosphere of the Earth, approximately 100,000 feet AGL, is readily available and closely resembles the atmosphere on Mars, in both temperature and density. This low density also allows normal size test geometry with a very low Reynolds number. This solves a problem in micro aerial vehicle development; it can be very difficult to manufacture instrumented test apparatus in the small sizes required for conventional testing. This thesis documents the design, construction, and testing of a glider designed to be released from a weather balloon at 100,000 feet AGL and operate in this environment, collecting airfoil and aircraft performance data. The challenges of designing a vehicle to operate in a low Reynolds number, low temperature environment are addressed.

Small UAV?s and flight vehicles in other atmospheres such as Mars are characterized by low Reynolds numbers. Low Reynolds number airfoil testing has been difficult to achieve and there are few centers that can accomplish this task. This study is an effort to develop a flight test system that will enable low Reynolds number tests to be performed with a simple glider design. The concept is to develop a high altitude glider that will be transported to altitudes reaching 100,000 feet or more by a helium filled balloon. At altitude, the glider will be released and will perform flight experiments as it descends. This region of Earth?s atmosphere, ?near space? has the conditions desired for low Reynolds number testing as well as similar properties to the surface of Mars. With the knowledge gained from this experiment, a better understanding of accomplishing flight on Mars may be attained.

The use of autonomous underwater vehicles (AUVs) for oceanic observation and research is becoming more common. Underwater gliders are a specific class of AUV that do not use conventional propulsion. Instead they change their buoyancy and center of mass location to control attitude and trajectory. The vehicles spend most of their time in long, steady glides, so even minor improvements in glide range can be magnified over multiple dives. This dissertation presents a rigid-body dynamic system for a generic vehicle operating in a moving fluid (ocean current or wind). The model is then reduced to apply to underwater gliders. A reduced-order point-mass model is analyzed for optimal gliding in the presence of a current. Different numerical method solutions are compared while attempting to achieve maximum glide range. The result, although approximate, provides good insight into how the vehicles may be operated more effectively. At the end of each dive, the gliders must change their buoyancy and pitch to transition to a climb. Improper scheduling of the buoyancy and pitch change may cause the vehicle to stall and lose directional stability. Optimal control theory is applied to the buoyancy and angle of attack scheduling of a point-mass model. A rigid-body model is analyzed on a singular arc steady glide. An analytical solution for the control required to stay on the arc is calculated. The model is linearized to calculate possible perturbation directions while remaining on the arc. The nonlinear model is then propagated in forward and reverse time with the perturbations and analyzed. Lastly, one of the numerical solutions is analyzed using the singular arc equations for verification. This work received support from the Office of Naval Research under Grant Number N00014-08-1-0012. / Ph. D.

Nowadays underwater gliders have become to play a vital role in ocean exploration and allow to obtain the valuable information about underwater environment. The traditional approach to the development of such vehicles requires a thorough design of each subsystem and conducting a number of expensive full scale tests for validation the accuracy of connections between these subsystems. However, present requirements to cost-effective development of underwater vehicles need the development of a reliable sampling and testing platform that allows the conducting a preliminary design of components and systems (hardware and software) of the vehicle, its simulation and finally testing and verification of missions. This paper describes the development of the HIL test bench for underwater applications. Paper discuses some advantages of HIL methodology provides a brief overview of buoyancy variation systems. In this paper we focused on hydraulic part of the developed test bench and its architecture, environment and tools. Some obtained results of several buoyancy variation systems testing are described in this paper. These results have allowed us to estimate the most efficient design of the buoyancy variation system. The main contribution of this work is to present a powerful tool for engineers to find hidden errors in underwater gliders development process and to improve the integration between glider’s subsystems by gaining insights into their operation and dynamics.

In this study, Computational Fluid Dynamics (CFD) simulations have been carried out in order to investigate and improve the performance of the Standard Cirrus glider, using different Navier-Stokes methods and solving the equations for the steady flow. The work has been divided in two parts: First, a study is performed to test the quality of the transition model (Gamma-ReTheta). The two dimensional results of the glider´s airfoil are compared against the results from panel’s methods and the open-source CFD codes: SU2 and OpenFoam. In addition, three dimensional glider´s models are simulated using the transition model with the purpose of creating a validated reference model of the glider’s performance in steady level flight. The simulations are carried out in two dimensions for the outer wing airfoil for a 1.5 e+06 Reynolds number and in three dimensions for the Wing & Fuselage model and Tail & Fuselage model under a range of velocities. Both simulations are validated against experimental data. In the second part of the study, the validated model is used to developed possible improvements in the glider´s external geometry that could produce possible benefits in the performance and handling qualities of the glider.

Various methods have been used, including airborne radars, LIDAR, observation of flying birds, towers, tethered balloons, and aircraft to gain both a qualitative and quantitative representation of how heat and moisture are transported to higher altitudes and grow the boundary or mixing layer by thermal updrafts. This paper builds upon that research using an instrumented glider to determine the structure and build a mathematical model of thermals in a desert environment. During these flights, it was discovered that the traditional view of a thermal as a singular rising plume of air did not sufficiently explain what was being observed, but rather another phenomenon was occurring. This paper puts forth the argument and a mathematical model to show that thermals actually take the form of a hexagonal convection cell at higher levels in the convective boundary layer when the thermal acts as if unrestrained by borders as in non-linear cases of free convection.

This paper details a method to compute absolute water velocity profiles from glider-based acoustic Doppler current profiler (ADCP) measurements based on the "shear method" developed for lowered ADCPs. The instrument is a 614-kHz Teledyne RDI ADCP integrated into the body of a Teledyne Webb Research Slocum Glider. Shear is calculated from velocity measurements and averaged over depth intervals to create a dive-averaged shear profile. Absolute velocities are computed by vertically integrating shear profiles yielding relative velocity profiles and then referencing them to dive-average velocity measurements calculated from glider dead-reckoning and GPS. Bottom-track referenced velocities also provide absolute velocities when bottom-tracking is available, and can be applied to relative velocities, producing absolute velocity profiles through linear fitting. Data quality control is based on ADCP percent good measurements. Compass heading bias corrections are applied to the raw ADCP measurements before averaging shear profiles. Comparison between simultaneous, full-water column velocities referenced to dive-average currents and those referenced to bottom-track profiles, resulted in RMS error values of 0.05 m s⁻¹ for both north and east components. During open ocean deployments, the glider ADCP recorded velocities concurrent and proximate to vessel ADCP measurements in waters of similar thermal characteristics. The combined comparison analysis resulted in RMS error values ranging 0.08-0.31 m s⁻¹ and 0.06-0.21 m s⁻¹ for north and east components, respectively. / Graduation date: 2013

Various methods have been used, including airborne radars, LIDAR, observation of flying birds, towers, tethered balloons, and aircraft to gain both a qualitative and quantitative representation of how heat and moisture are transported to higher altitudes and grow the boundary or mixing layer by thermal updrafts. This paper builds upon that research using an instrumented glider to determine the structure and build a mathematical model of thermals in a desert environment. During these flights, it was discovered that the traditional view of a thermal as a singular rising plume of air did not sufficiently explain what was being observed, but rather another phenomenon was occurring. This paper puts forth the argument and a mathematical model to show that thermals actually take the form of a hexagonal convection cell at higher levels in the convective boundary layer when the thermal acts as if unrestrained by borders as in non-linear cases of free convection.