**1.2. Literature review**

A brief review of the literature is described in this section in chronological order.

Ref. [5] conducted experiments on a systematic series of 24 mathematically related streamlined bodies of revolution to measure drag force, Reynolds stresses, pressure, kinetic energy, axial and radial velocity profiles, stern and far wake at deep submergence. The body geometric parameters are fineness ratio, prismatic coefficient, nose radius, tail radius and the position of the maximum section. The mathematically derived series of bodies of revolution, which was designated series 58, are used to form the offsets of the models using a sixth degree polynomial.

Ref. [6] conducted experiments on a 1:6 spheroid (MS) of 1.578 m long and 25 cm maximum diameter in a wind tunnel at a speed of 12 m/s and measured pressure distributions, mean velocity profiles, and Reynolds stresses in the thick axisymmetric turbulent boundary layer near the tail of the body. The thick boundary layer is characterized by significant variations in static pressure across it and very low level of turbulence. It is concluded that the static pressure variation is associated with a strong interaction between the boundary layer and the potential flow outside it, while the changes in the turbulence structure appear to be a consequence of the transverse surface curvature. The main conclusion was that by using the thin boundary layer calculation it is not possible to predict the behavior of the flow in the tail region of a body.

Ref. [1] introduced an automatic synthesis approach to minimum drag axisymmetric hull shapes in non-separating flow with constraints on volume and speed. The optimization was done in a finitely constrained parameter space with eight-parameter 'rounded-nose- tail boom' bodies. The parameters are the zero radius of curvature of the nose, maximum diameter and its axial location, curvatures at the locations of the maximum diameter and aft inflection point, radius and slope at the aft inflection point and the terminal radius of the profile. The drag was evaluated exploiting laminar flow by avoiding flow separation. Ref. [7] developed a multicriteria optimization model for ship design which is a problem with multiple local optima with widely varying sets of designs. Simulated annealing had been successfully implemented to optimize the ship design process as a global optimization tool. The decision system was based on the analytic hierarchy process.

Ref. [8] discussed the Approximation Management Framework (AMF), for solving optimization problems which aims to use the cheaper low fidelity models in iterative procedures with occasional, but systematic, recourse to expensive high fidelity models. Three versions of AMF using nonlinear programming algorithms are implemented on a three dimensional (3D) aerodynamic wing and a two dimensional (2D) airfoil. The three methods discussed were augmented Lagrangian AMF, sequential quadratic programming AMF and AMF based on 'multilevel algorithm for large scale constrained trust-region optimization'.

Ref. [9] worked on implementing a downhill simplex method with constraints on volume displacement and transverse moment of area of water-plane of a ship to minimize its total drag. The parent hull form considered is classical Wigley hull of length 122 m defined by NURBS (Non-Uniform Rational B-Spline) surface. The ITTC formula is used to calculate the frictional drag and the wave drag was predicted using zeroth-order slender-ship approximation. Ref. [3] developed two simulation based ship design approaches, one of which is 'narrow band derivative-free' approach and the other is 'variable fidelity' approach. They used CFD to evaluate the objective function, which is the total drag of a ship, and validated the results by conducting model tests. Similar work was done by [10, 11].

Ref. [12] studied practical and quantitative methods for measuring effectiveness in naval ship design. A method is presented that uses the analytic hierarchy process combined with multi-attribute value theory to build an overall measure of 'effectiveness' and 'overall measure of risk function' using trained expert opinion to replace complex analysis tools. Ref. [13] implemented topological optimization techniques to reduce the weight of the composite advanced sail structure. The approach is applied to reinforcement layout optimization under an asymmetric wave slap loading condition. A high complexity model in the form of multilayered shell and a low complexity model in the form of stiffened shell are developed for layout optimization. Ref. [14] developed a framework for design optimization for problems that involve two or more objectives which may be conflicting in nature. The framework is implemented for the design of space propulsion involving a response surface based multiobjective optimization of a radial turbine for a liquid rocket engine. The surrogate model is integrated with GA-based Pareto front construction and can be effective in supporting global sensitivity evaluations. It has been concluded that a global sensitivity analysis provided a summary of the effects of design variables on objective function analysis and it is determined that no variable could be eliminated from the analysis.

Ref. [15] developed an underwater glider ALEX with independently controllable main wings and conducted wind tunnel experiments. To establish a mathematical model of the glider CFD is used to estimate the hydrodynamic forces acting on it and the results were compared with the experiments. Ref. [16] implemented a simulated annealing technique for the shape optimization of Cormoran AUV operating at snorkeling depths with constraints on surface area and volume and validated the results by conducting experiments. The objective was to minimize the wave making resistance at snorkeling depths while using an empirical formula for the calculation of the viscous drag. Ref. [17] developed a design optimization process for AUV using GA with cost, effectiveness and risk as the main design objectives. The design parameters are diameter, length to diameter ratio, forward shape coefficient, aft shape coefficient, endurance, speed, communication, payload, propulsion, battery and electronics configurations, wall thickness and material.

Ref. [18] studied the drag and turbulent noises created by the equipment like sonar array, electronic devices, antennas and video cameras. Automatic multi-objective optimization is applied using 'design of experience' as well as GA. Ref. [19] developed a Multidisciplinary Design Optimization (MDO) approach to the design of submarine considering four objectives, namely, deck area, drag, structural design and maneuvering. Particle Swarm Optimization (PSO) technique is used. The length of the parallel middle body, maximum diameter, tail shape parameter and nose shape parameter are the design variables. Ref. [20] developed an AUV PICASSO (Plankton Investigatory Collaborating Autonomous Survey System Operon). To improve the overall propulsive performance and maneuverability numerical and experimental study has been carried out and concluded that by changing the fore and aft hull form propulsive performance has been improved.

Ref. [21] developed a hybrid driven underwater glider Petrel. CFD simulations were carried out to study the glide mode of the glider. The glide efficiency is found to be significantly influenced by the chord length of the wing, the stability of the vehicle is influenced by the sweep angle of the wing and the glide stability is influenced by the location of the wing. Ref. [22] developed the Flinders AUV. Shape optimization of the vehicle with a ducted propeller has been carried out using CFD software. The Design of Experiments (DOE) method based single objective optimization problem with minimizing drag as the objective has been formulated and solved with location of the sail, the separation between sail and transponder and angle of attack of the nozzle as the variables. Ref. [23] developed an approach to characterize the spiraling motion of underwater gliders and applied on Seawing underwater glider. The hydrodynamic coefficients are computed using CFD. The proposed approach has been validated by conducting field experiments. Ref. [24] investigated hydrodynamic characteristics like drag and lift forces of the USM shallow underwater glider whose length is 1.3 m with 0.17 m diameter by using CFD.
