Elementos del Marco conceptual

The CCPP is a novel propeller, which has useful capabilities such as high manoeuvrability. The CCPP is able to assist an underwater vehicle to perform complex manoeuvres such as up and down, side to side, forward and backward, and pitch and yaw.

The CCPP was built in 2005. The built CCPP was only tested in order to demonstrate that the built CCPP could generate axial and side thrusts. In the test, the CCPP was tested in a bollard pull condition without any underwater vehicle body or fairing. That study did not represent the performance of the CCPP.The first research question arises from the uncertainty of the performance of the CCPP. The true performance of the CCPP was assessed. In the experiment, the CCPP was attached behind an underwater body and to all fairing. Its true propulsion performance in a straight line was conducted in the Towing Tank at the Australian Maritime College. The details of the experiment are presented in Chapter 4.

The second research question is whether the CCPP can be utilized to propel an underwater vehicle. There are several tasks to be completed before the answer is positively confirmed. The most important work is the completion of a control program required to control collective and cyclic pitches and to control the RPM of the main shaft of the propeller. With only the basic developed control system and many uncertainties of the hydrodynamic characteristics of the CCPP, which may cause the underwater vehicle to be uncontrollable, the following issues may cause difficulties in controlling the CCPP:

 According to Humphrey (2005), if the thrust coefficient, KT, variation with blade

angle was nonlinear, the CCPP could be difficult to control.

 According to Humphrey (2005), the measured thrust directions were not the same as the assumed thrust directions because the oscillating blades of the propeller created an unsteady flow effect. In his preliminary test, the unsteady flow effects were found dependant only on the axial thrust magnitude.

 In addition, a generated torque is inherent when the propeller is operating. A cylinder- shaped underwater vehicle tends to roll if it does not have any devices that can generate torque to counter the generated torques from the propeller.

 When an underwater vehicle is operating, the observation is limited. The operator cannot see the orientation of the vehicle, and the lack of this information could cause a disaster to an underwater vehicle.

 At the current control system, the control signals are simultaneously sent to the actuators. It is the cause of the unsmooth and uncontrollable paths of the direction of the thrust during the transition of the thrust direction.

These issues lead to the third research question, that is, whether an underwater vehicle with the CCPP can be controlled by any operator with only minimal training. In order to shorten the learning period, all mentioned issues must be overcome. The control algorithm of the blade angles must be modified to compensate for the nonlinearity in the response curve of the thrust coefficient, KT, to provide a linear thrust output for operations of a vehicle. The control

algorithm that can provide a linear thrust output is simple and intuitive for an operator to understand the control system. The thrust coefficient, KT, in various conditions can be

quantified by conducting the captive experiments. The experimental data can also be used for the issue of lagging of thrust direction.

The fourth question is whether the performance of the CCPP can be predicted by numerical methods. The blade element method can be used to model the unsteady hydrodynamic effects. The most elementary calculation of blade forces is based on a 2-D thin airfoil theory. This theory does not model the wake from the neighbouring blades; however, it allows convenient analytical mathematical solutions to be incorporated into the rotor analysis. The 2-D thin airfoil theory provides a considerable level of analysis of the problem and good insight into the response of the unsteady behaviour (Leishman, 2006, p. 428). The problem of an oscillating blade was considered. In this problem, the indicial response theory created by Wagner (1925) can provide a solution for the indicial lift on a thin airfoil undergoing a transient step change in an angle of attack in an incompressible flow (Leishman, 2006, p. 446). After the implementation of the prediction performance program, the program was integrated into the simulation program.

A development of an AUV is very expensive and time consuming. A lot of money is spent on hiring a researcher, hiring a support crew, purchasing equipment, and using test facilities. In addition, the development will be a disaster if the research team lost a developed AUV during field testing because of a malfunction of a vital system. Therefore, the numerical simulation software of an underwater vehicle is a valuable tool for a development team. The simulation

program can provide the position, orientation, and velocity of an underwater vehicle. The program utilized information about the performance in a straight line of CCPP assessed in the experiment, the development of the numerical prediction program, and the hydrodynamic coefficients. These hydrodynamic coefficients describe the hydrodynamic forces and moments acting on an underwater vehicle. There are many ways to estimate the hydrodynamic coefficients. A general method to estimate the coefficients of an underwater vehicle is by conducting an experiment using the planar motion mechanism. Another estimating method is semiempirical methods. More details of semiempirical methods can be found in the work of Jones et al. (2000). Another method is to use computational fluid dynamics (CFD) software to estimate the coefficients. This research deploys a semiempirical method.

1.4 Research Outcomes