## 1 Introduction
### Underwater Glider (UG)
[12] used the UG optimal control of trajectory and navigation accomplished through linearization of the non-linear model and the use of the _Linear Quadratic Regulator_ strategy, enabling the robot to follow the path reference in a diving maneuver of short duration which complies with the necessity to save energy and increase the range. Geometry-wise studies include various pressure hull and wing system configurations. [PERSON] et al. [13] published a paper on the development of dual buoyancy Ray-Type UG, which belongs to a family of flying wing configurations. The shape of this manta-ray-inspired platform allows for a larger payload of battery and sensors. Therewith, the analysis of fluid resistance performance was carried out through Computational Fluid Dynamics (CFD), followed by a simulation of gliding dynamics. In [PERSON] et al. [14], the shape of UG was optimized based on an approximate model technology. [PERSON] et al. [15] explored the winglet effect on both hydrodynamics and the trajectory of a blended body UG. [PERSON] et al. [16] investigated the influence of the wing position of the dynamics of UG. Other endeavors regarding the UG configuration include the modeling and simulation of a disk underwater glider with issues covering its dynamic stability as well as a structural selection and numerical analysis of its pressure hull, [PERSON] et al. [17], [PERSON] [18]. In [PERSON] et al. [19], the 3D CFD model was created to enable the simulation of a UG motion in six degrees of freedom for a small Reynolds number including the numerical integration of the equations of motion of an underwater glider shaped as a body of revolution with wings (BRW). In order to provide an adequate accuracy of the flow calculations, the authors independently meshed the domain surrounding lifting elements and the far-field around it, claiming that replacing the deforming meshes approach with the one using sliding meshes results in a high accuracy of force prediction. Energy consumption estimation and minimization is one of the major issues discussed by the community of researchers implementing UG technology. [PERSON] et al. [20] applied the motion parameter optimization for different observation missions for Petrel-L UG in order to maximize the gliding range and minimize the energy consumption for one gliding cycle. They used the _inner penalty function method_ and adopted a certain nonlinear variation rule of the buoyancy loss. The authors stated that the proposed gliding strategy could increase the gliding range by 24% for the UG Petrel-L. Considered in [PERSON] et al. [21] are a set of issues related to the design and motion simulation of a new UG for the depth of 400 m and a speed of 2 knots on the basis of a steady-state attitude formulation accounting for net buoyancy, and the displacement of a movable mass-block. [PERSON] et al. [22] discusses the multi-disciplinary optimization of UG for improving endurance. The authors focus their attention on the design parameters which have significant influence on the gliding range for one cycle seen as the optimization target. These include the buoyancy factor, the compressibility of the pressure hull, hydrodynamic coefficients and motion parameters. The results, as claimed by the authors, show a significant increase of the gliding range. The analysis performed for the Petrel-L UG comprised matters of hydrodynamic configuration (body and wings geometry) and the pressure hull subsystem. The authors indicated that the Petrel-L UG designed with the proposed optimization approach was tested during two sea trials in the South China Sea. It is worthwhile mentioning that the motion parameter optimization should account not only for the variation of net buoyancy but also for such effects as the deformation of the pressure hull and the variation of sea water density. [PERSON] et al. [23] state that the buoyancy variation caused by these two factors is of the same order of magnitude as the nominal net buoyancy. Underlined in [PERSON] et al.