Performance analysis and simulation of an autonomous underwater vehicle equipped with the collective and cyclic pitch propeller

There is a growing need within marine sciences and engineering that requires the torpedo shaped Autonomous Underwater Vehicles (AUVs) being capable of accomplishing various complex surveillance missions, including scientific, commercial and military applications. Be-sides the traditional research on the control and navigation of an AUV, the propulsion system study becomes more and more essential to increase the manoeuvrability and efficiency of AUV. The conventional propulsion system with fixed pitch propeller (FPP) and control surfaces at the aft end is the predominant propulsion type used by AUVs. This propulsion configuration has the shortcoming of insufficient low-speed manoeuvrability since the control surface manoeuvring forces are only generated when the vehicle is in motion. This is one of the fundamental limiting factors for the current torpedo shaped AUVs. The development of new propulsion system enabling both low speed and cruising speed operations could expand the typ-ical operational envelope of an underwater vehicle and pave the way for the new applications. This thesis focuses on the characteristic analysis of an innovative propulsion system called the Collective and Cyclic Pitch Propeller (CCPP) and the manoeuvring performance of an AUV equipped with CCPP. In the CCPP mechanism, the angles of each propeller blade can be positioned periodically during a rotation in both collective and cyclic pitch setting. CCPP has the capability to provide continuous propulsive force and manoeuvring forces simultaneously. The primary task of the thesis was to explore the feasibility of a prototype CCPP to an under-water vehicle by numerically conducting the comparison between the AUV equipped with CCPP and FPP in standard manoeuvring tests. Initially, the Experimental Fluid Mechanics approach was utilised to investigate the performance and derive the mathematical models of the CCPP and FPP. Two separate experimental apparatus were designed and implemented in this research for CCPP and FPP system. In the first experiment, the dynamic modelling of FPP using the four-quadrant model was proposed based on experimental data. The second exper-imental study involved the extensive investigation of the CCPP to establish its hydrodynamic characteristics. A series of comprehensive bollard pull and captive model tests were designed and conducted to evaluate the propulsion performance. Furthermore, the research developed a numerical simulation program called AUVSIPRO to examine the performance and manoeuvring characteristics of an AUV equipped with the CCPP as well as conventional configuration FPP. The Gavia AUV was used as the research platform and its mathematical model with non-linear hydrodynamic coefficients were defined using the theoretical approach. Standard manoeuvring tests of marine vehicles were fully presented in the simulation program to analyse the manoeuvrability. In addition, the results from the experiments and simulation were utilised in the comparison study between the CCPP and conventional configuration applied to AUV. Finally, the controller design for an AUV equipped with a CCPP was conducted. The two-stage system identification method was proposed to develop the linear system model, which was applicable for the control design. The optimal state feedback algorithm was presented as the control strategy. The propulsion systems for AUV have been subject to an increased focus with respect performance and manoeuvrability. This research is an exploration into the feasibility and viability of CCPP propulsion system for a torpedo shaped AUV and contributes to the areas related to the development of propulsion system for an underwater vehicle

Magnitude and phase shift of the side-force generated by a collective and cyclic pitch propeller

Almost two-thirds of the earth's surface is covered by water and hidden beneath the water surface remains a vast world yet to be discovered. The high risk and dangerous nature of underwater reconnaissance has resulted in the development of a wide variety of unmanned exploration vehicles. An example of such a vehicle is the Autonomous Underwater Vehicle (AUV), a programmable submersible capable of conducting a pre-determined mission autonomously over large distances and lengths of time without the need for additional human interaction. Since the 1970s AUVs have become the preferred underwater exploration tool in many industries and fields of research, e.g. oil industry, geographical surveying, marine biology, and even military applications. Successful completion of such AUV missions requires a vehicle design that combines long-endurance travelling efficiency with effective operation at low speeds. Considering that traditional control surfaces lose their efficiency at low speeds and low speed manoeuvring aids such as side- or podded-thrusters reduce the long-endurance travelling efficiency, a design issue arises. The design trade-off between travelling range and low speed manoeuvring compromises and limits the performance of AUVs and needs to be addressed accordingly. The work outlined in this thesis investigates the hydrodynamic performance of a novel AUV propulsion and manoeuvring concept, the collective and cyclic pitch propeller (CCPP). Aimed at addressing the aforementioned design issue, the CCPP is an extension of the traditional controllable pitch propeller and applies helicopter technology to achieve advanced control of the propeller blade pitch, i.e. orientation of the blade. As such, the CCPP provides effective and efficient propulsion and manoeuvring forces for an AUV at both high and low forward velocities. The current work focused on investigating the manoeuvring or side-force generated by the CCPP. As such, the performance of the CCPP's side-force generation is quantified by both the magnitude and phase shift of the side-force. The magnitude defines the force generation's effectiveness in manoeuvring the AUV, while the phase shift, as a result from a discrepancy between the intended and resulting force orientation, characterises the efficiency of the AUV manoeuvring. The project objectives were achieved through the extensive development of a numerical methodology to simulate, analyse, evaluate, and improve the CCPP's hydrodynamic performance. Both two-dimensional and three-dimensional periodic unsteady Reynolds-Averaged Navier-Stokes models (URANS) were developed, providing the necessary tools to numerically (re-)design the force generated by the CCPP. The developed three-dimensional methodology is shown to be suitable for the evaluation of the CCPP's current performance, analysis of further design alternatives, and even the assessment of complete new prototypes. In essence, the methodology has become a useful and powerful tool for the development of the CCPP into a viable and realisable propulsion and manoeuvring system for AUVs. Results show that the CCPP was able to generate a large, and thus, effective side-force under the various simulated operational conditions. However, for both bollard pull and captive conditions, the side-force generation is observed to be highly dependent on the generated drag force at high (collective) pitch angles. Because of the associated drag forces, the side-force generation at high pitch angles becomes highly inefficient, with large side force phase shifts occurring. The associated misorientation of the side-force cannot be compensated for efficiently by adjusting the control algorithm without affecting the overall propeller efficiency. At lower pitch angles, variation of the cyclic pitch resulted in the generation of an efficient but ineffective side-force, i.e. a (relatively) small side-force magnitude combined with a low side-force phase shift. To achieve a larger side-force magnitude at lower pitch angles, the effect of increasing the size of the propeller blades is simulated and evaluated. The applied increase in blade size has to be carefully balanced to avoid a compromised overall efficiency of the side-force generation. Through the developed numerical method, evaluation of potential shifts in operating and design conditions has been shown possible and a rationalised solution has been proposed

AUVSIPRO - a simulation program for performance prediction of autonomous underwater vehicle with different propulsion system configurations

Autonomous Underwater Vehicle (AUV) is a growing technology with a great potential to both military and civilian applications. Extensive developments and advanced innovations of AUV have been introduced in recent years from various research centres around the world. Among the fundamental modules of an AUV, the propulsion system strongly affects the vehicle performance. The increasing complexity in missions and operational environment require the propulsion system to offer high efficiency and excellent maneuverability. In this study, an AUV simulation program named AUVSIPRO is proposed in the preliminary design stage to predict and compare the AUV manoeuvrability equipped with different propulsion configurations. A series of primary manoeuvres standard for underwater vehicles are presented to investigate the system feasibility. In order to derive the mathematical model in the simulator, the propulsor models are experimentally conducted in the Towing Tank, the hull hydrodynamic coefficients are calculated using analytical, and system identification approaches. The system outputs are achieved by numerical method. The simulation program provides an effective platform to examine different the propulsion system configurations to an AUV as well as a torpedo shaped submarine