# Development of a Mobile Buoy with Controllable Wings: Design, Dynamics Analysis and Experiments
## 2 Mobile Buoy with Controllable Wings  
The proposed mobile buoy aims to obtain a higher level of integration between a buoyancy-driven underwater glider and a conventional Argo profiling buoy, making it more compact and easier to perform continuous observations at a multiscale range. Figure 2a shows the shape and internal structural design of the mobile buoy. The internal structure of the buoy is identical to that of a conventional underwater glider, primarily comprising a buoyancy regulating system, control system and battery components. Unlike conventional underwater gliders, the attitude of the proposed mobile buoy can be controlled by adjusting the rotation angle of the wings, thus switching between Argo mode and Glider mode. To describe the rotational state of the wing clearly, the definition of wing rotation angle \(\alpha_{w}\) is introduced in Figure 2b. The longitudinal axis of the fuselage (L-axis) coincides with the direction of antenna installation, and the horizontal axis of the fuselage (H-axis) that along the central axis of the spherical pressure shell is perpendicular to the L-axis. \(\alpha_{w}\) is the wing rotation angle (the angle where the wing axis intersects with the H-axis). During underwater navigation, the mobile buoy achieves up and down motion driven by the net buoyancy and is propelled forward by the horizontal lift component acting on wings. In this paper, two operation modes are divided by the range of wing rotation angles: Argo mode (\(-80^{\circ}\leq\alpha_{w}\leq-90^{\circ}\) or \(80^{\circ}\leq\alpha_{w}\leq 90^{\circ}\)) and Glider mode (\(0^{\circ}<\alpha_{w}\leq-80^{\circ}\) in climbing, \(0^{\circ}<\alpha_{w}\leq 80^{\circ}\) in diving) by regulating \(\alpha_{w}\) to control the ratio of horizontal displacement to diving depth to change the glide angle, as shown in Figure 2b. To ensure that the hydrodynamic forces acting on the fuselage are consistent in all directions, the shape of the mobile buoy is designed as a circular sphere consisting of two hemispherical pressure shells, thus contributing to the stability of the mobile buoy in both two motion modes. Stability is a critical aspect in the design process, which needs a reasonable arrangement of the internal configuration. For the proposed mobile buoy, the center of gravity is under the center of buoyancy and both are located on the same vertical line. In addition, the batteries and associated hardware of the buoyancy regulating system can be arranged at the bottom of the mobile buoy, which can provide the restoring moment to improve stability.  
Figure 1: Working scheme of the mobile buoy.  
In the previous studies of buoys and underwater vehicles, most of them improved the maneuverability of the buoys by equipping mobility apparatuses and propellers, or enabled multi-mode integration for the vehicles through complex control systems, without considering the use of controllable wings to achieve simpler integration with profiling buoys and underwater gliders. In this study, a novel mobile buoy with controllable wings was developed to combine the positive attributes of Argo profiling buoy and underwater glider. The novel mobile buoy can achieve forward motion by utilizing the horizontal component of wing lift, which is different from prior research focused on enhancing buoy maneuverability through the addition of propellers. Meanwhile, it also overcomes the limitation of high energy consumption associated with traditional mobile buoys during propeller propulsion. Moreover, it simplify the internal structure by controlling wing rotation for operating modes switching, which is different from previous designs of multimode underwater vehicles.