Optimization of thrust propeller design for an ROV ( Remotely Operated Vehicle ) consideration by Genetic Algorithms

Remotely Operated Vehicle (ROV) is one of the technology that can facilitate for observing and exploring the underwater condition (sea). The design and manufacturing process of underwater robots needs many support and increase the performance of the underwater robot to do some missions. Thruster is one of main component which has function as an actuator during the operation. In the present study, propeller design the most important for solving the problem of an ROV. For the optimization of thrust, Genetic Algorithms (GA) can powerfully search for parameters in large multidimensional design space. Thus, the principle can be applied for determining the initial dimension of the propeller for producing optimum thrust of ROV. GA was successfully shown able to obtain an optimal set of parameters leading to propeller characteristics and best performances. Nomenclature AE propeller expanded area Sn exponent of J A0 propeller disk area T thrust CTn regression coefficient of thrust coefficient tn exponent of P/D CQn regression coefficient of torque coefficient Un exponent of AE/A0 D diameter propeller Vn exponent of Z J advance coefficient Z number of blades KT thrust coefficient ρ density of water KQ torque coefficient n propeller rotating speed P propeller blade pitch P/D pitch diameter ratio Q torque (Nm) Corresponding author: aldias@pukyong.ac.kr © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 138, 07003 (2017) DOI: 10.1051/matecconf/201713807003 EACEF 2017


Introduction
Remotely Operated Vehicle (ROV) is an instrument formed mini-sized submission vehicle.ROV is usually to explore underwater object, such as underwater photography, military operation and underwater pipeline repairing.ROV is used for activities in humanunreached area like an underwater small cave.ROV is designed to have abilities to rescue operation and repairing of object from the surface [1].
Underwater robot design and manufacturing absolutely requires many supporting components to improve the underwater robot operation to perform a variety of underwater missions.Thruster is one of main components as locomotor of underwater robot to maneuver horizontally when it moves forward and backward and vertically to moves up and down [2].
The first proposal to use screw propeller appears to have been made in England by Hooke in 1680 [3].The genetic algorithms are one of method that has tool for optimization for many difficult optimization problems with multi objectives.GA methods were shown to be able to replace the traditional computation method and design charts.In this case for determining the initial propeller that optimum for ROV thruster is difficult.For selecting the initial propeller, used optim-tools in Genetic Algorithms.However, the traditional design charts method and previous GA methods were limited in considering or maximum of hydrodynamic aspect, such as efficiency, thrust coefficient, etc. hence, the goals of present research to determine the optimum value of thrust for ROV by 3 parameters, pitch diameter ratio, expanded blade area ratio, and rotational speed of propeller.Applying GA methods to propeller design with consideration of thrust for reaching the best performance of propeller.

Propeller design
The preliminary propeller design problem is described in detail in the principles of Naval Architecture.Here is the basic design or initial design of propeller with the dimension for dependent variables as shown in Table 1.For independent variables as presented in Table 2

Parameters of optimization
Selecting from a propeller series is a simple method to design a propeller.Among the series propeller is one of the most often used and studied [4].And selection of the table was improved later.

Genetic algorithms (GA)
The basic theory has been described [5].Genetic algorithms are search algorithms based on the mechanics of natural selection and natural genetics.They combine survival of the fittest among string structure with structured yet randomized information exchange to inform a structure algorithms with some of the innovative flair of human search.
Based on the theory, the research was conducted with set of parameters dependent and independent variables.For the first steps were identifying variables and functions the propeller of ROV.There are three variables that we could change randomly as like as P/D 9pitch ratio), AE/A0 (expanded blade area ratio), and n (rotational speed).From this process, we could get the value of KT and KQ.Thus, the thrust (T) amd torque (Q) can be expressed in Eq.1 and 2.

Function:
The fitness function we used as the functions of the blade number, blade area ratio, pitch ratio and advanced coefficient can be described in the Eq.6 and 7.

Fitness function:
Where CTn and CQn are the regression coefficients of the thrust and torque coefficients respectively, Sn, tn, Un and vn are exponents of J, P/D, AE/A0, and Z respectively.
The constraint function can be created in Eq.5 and 6.

Optimization procedures
For the process of optimization shown in Fig. 1.The optimization tools which is supported by MATLAB program for the solution of genetic algorithms method.This study, GA apply to know how is the optimum thrust for the initial propeller using the parameters and setup for GA is shown in Table 3.

Optimization Output
The output of optimum thrust can be shown in Table 4.And results can be exported by genetic algorithms as shown in Fig. 2.

Fig. 2. Fitness value through the generations
At the 51 iterations using GA, the thrust will be optimum when the value of P/D (pitch ratio) is 0.60, AE/A0 (expanded area ratio) is 0.79 and the value of rotational speed is 5 rps.

Final Results
The difference of computational result can be seen in Table 5.

Conclusion
In this paper, study on development of the propulsion device for an ROV (Remotely Operated Vehicle).The GA is applied for optimization design of the initial propeller dimension and the results show that it is good for kind of the problems.The optimization of propeller for an ROV has been proposed and provides the solution to ROV thruster and GA optimization can be employed due to propeller performances.
results, the thrust is increasing 27.43% from 2.530 N to 3.224 N. it means the optimization of the thrust for the propeller of ROV is reached and satisfied.And results of new design as shown in Fig.3for the streamline simulation and Fig.4for the pressure contour.