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Wave glider is an unmanned surface vehicle that can directly convert wave energy into forward propulsion and fulfill long-term marine monitoring. A previous study suggested that the wave motion and stiffness of restoring springs mounted on the hydrofoil are the main factors affecting the propulsion performance of the wave glider. In this paper, the dynamic responses and nonlinear characteristics of the underwater propulsion mechanism considering the nonlinear stiffness of restoring springs are investigated based on a fluid–rigid body coupled model. Firstly, models of propulsion mechanism with different kinds of restoring springs are proposed, and the linear and nonlinear characteristics of the restoring spring are considered. Then, a fluid–rigid body coupled model of a wave glider is developed by coupling the rigid body dynamics model and hydrodynamic model. Dynamic responses are simulated by the numerical analysis method, and the nonlinear characteristics with different restoring springs are illustrated by the time/frequency domain motion response and phase diagram analysis. The effects of the wave excitation frequency, wave heights and the location of the connection point of springs on the propulsion performance of the wave glider are analyzed. The results show that multi-frequency responses occurred in the propulsion system, and the nonlinear restoring spring on the hydrofoil can provide a larger restoring moment to avoid excessive pitch angle and is more suitable for different sea conditions, which provides a reference for developing propulsion mechanisms with high performance in complex marine environments.

Wave Glider is an autonomous surface vehicle that directly uses wave energy to generate forward power and has been widely used in marine survey and observation. Wave Glider is composed of surface vessel, submersible propeller and the connection structure between them. Connection types are thought to be related to the performance of Wave Glider closely. In this paper, the effects of the connection structure between the surface vessel and the submersible propeller on the motion performance of the Wave Glider are studied. Several connection types such as rigid rod, cable, multi-link chain and elastic rod are applied to connect the surface vessel and the submersible propeller. The models of connection structures are developed respectively. Among them, cable model is established with a finite number of small cylinders, which connected by spring and damping elements; multi-link chain can be seen as hinged by multiple rigid rods; elastic rod model can be looked on as several segments linked with elastic components. Considering the connection characteristics, the integrated dynamic models are established by applying multi-body dynamics software ADAMS (Automatic Dynamic Analysis of Mechanical Systems) with consideration of the hydrodynamic forces on different components of Wave Glider. The propulsion performance of the Wave Glider is calculated by using numerical method, and the simulation results showed that the difference of propulsion performance with different connection types of the Wave Glider is slightly. But serious impacts can occur on the connections of rigid rod and multi-link chain. They can lead to serious extra load on the structure of Wave Glider. From the engineering practice of Wave Glider application, the cable connection is more convenient to transport, deploy, recover and store. It is also the generous connection type for wave glider.

Marine monitoring equipment such as Argo profiling buoys and underwater gliders are important devices for oceanographic research and marine resource exploration. In this study, a novel mobile buoy capable of vertical profiling motion like Argo profiling buoys and sawtooth gliding motion like underwater gliders is proposed. The proposed mobile buoy can switch between the two motion modes with controllable wings. To verify the feasibility of the proposed mobile buoy, a fluid–multibody coupling model considering multibody dynamics and hydrodynamics was developed to investigate the dynamic response. A scaled-down buoy prototype was fabricated and the feasibility of the two motion modes was experimentally investigated in a laboratory tank. The experimental results agree well with the results of numerical simulation. This work can be helpful for the design and analysis of this kind of mobile buoy.

A wave glider is a novel unmanned marine vehicle which can convert marine energy into kinetic energy. In practice, it is crucial for the wave glider system to deploy into the ocean environment efficiently and safely. Hence, the present work establishes the wave glider motion equations to analyze the deployment method. Firstly, the wave glider model is simplified in the vertical plane and the cable model is defined as mass nodes connected with a massless spring. Then, two typical deployment methods (Method 1 and Method 2) are proposed based on the multibody dynamic method, and the numerical simulation model is established to investigate the kinematic performance of two deployment methods. Lastly, the dynamic characteristic analysis is conducted to select the determined deployment method. We explain the practical advantages of Method 1, which would provide the reference for the deployment method selection.