## 1 Introduction
### Wave Glider (WG)
To secure efficient wave-driven propulsion, one needs to use low-drag and stable upper displacing modules. [PERSON] et al. (2018) employed the Wigley model as the surface boat of the Wave Glider and calculated its resistance characteristics at a range of Froudenumbers. [PERSON] et al. [33] explored the overall stability performance of alternative hull forms of an Automated Oceanic Wave Surface Glider Robot using the Maxsurf software. In [PERSON] et al. [34] a numerical investigation of a Liquid Robotics type WG in head seas has been conducted with the use of a combination of commercial CFD packages Fine/Marine and STAR-CCM+. First, a simulation with the use of unsteady Reynolds Averaged Navier-Stokes (URANS built FINE/Marine with volume of fluid model-VOF) was executed regarding the flow around both the surface boat and the wing module. Secondly, using an overset mesh, a high-fidelity simulation of the passive eccentric rotation (PER) of the underwater hydrofoils was conducted. It was found that this rotation, coupled with a surge force acting upon the WG, is the main factor defining the propulsion efficiency of the vehicle. Not that the effect of the springs periodically returning wing elements to initial positions throughout oscillation cycles was modeled both in the experiment and in computations. [PERSON] et al. [35] established a cable model of a wave glider by considering connection characteristics such as a rigid rod, cable, multi-link chain and elastic rod. The results showed that the propulsion performance with different connection types of the wave glider was slightly different. [PERSON] and [PERSON] [36] studied the motion relationship between the float and the sub glider by MATLAB. [PERSON] et al. [37] studied a restricted circle-based position-keeping strategy for the wave glider. They found that under a given sea state, a smaller restricted circle ensures a better positioning accuracy, but requires more energy consumption. They also concluded that waves and currents both have significant impacts on the positioning accuracy and energy consumption for the wave glider position keeping. [PERSON] et al. [38] numerically investigated the case of a semi-active flapping foil of the WG of NACA0012 cross-section with fully prescribed heaving motion and the pitching motion determined by the hydrodynamic force and torsion spring. Analyzed in this paper were the influences of reduced frequency, spring stiffness and critical pitching amplitude on the hydrodynamic characteristics. The authors found that propulsive performance of the foil depends on whether the reduced frequency is lower or higher than the so-called _critical_ reduced frequency. In the former case, the propulsive performance of the flapping foil can be improved exponentially, whereas in the latter case the semi-active flapping foil cannot provide an effective thrust. [PERSON] et al. [39] examined the use of four machine-learning frameworks to predict the speed response of the SV3 Wave Glider on timescales relevant to local motion planning. According to this paper, the models were trained using onboard measurements of incident waves and near-surface currents. The research draws on a 71-day dataset collected during two deployments conducted between October and December 2020 and April and June 2021 off the coast of Southern California. The observations span a wide range of environmental conditions, with significant wave heights and near-surface flow speeds ranging up to 6 m and 0.8 m/s respectively. The predictions generated by the best-performing models showed good quantitative agreement when evaluated with multiple independent datasets, indicating that the selected features and models generalize well. [PERSON] and [PERSON] [40] developed a mathematical model of a ship with energy-saving wings, allowing to calculate the motions of the ship-plus-wings system induced by regular and irregular head waves.