Zhiliang Wu

Structure Optimal Design and Performance Test of Airfoil Shear Probes

Airfoil shear probes are instruments used to measure the turbulent kinetic energy dissipation rate in the ocean. The cantilever beams and piezoelectric ceramics sheets are core components of shear probes. The former is the force transferring unit that amplifies the shear force acting on the probe tip. The latter is the piezoelectric transduction element that transforms force to electrical charges. As obbligato components for shear velocity measurement, both the cantilever beam and piezoelectric ceramics sheet have significant influence on the performances of the sensor. Optimizing the dimensions of the cantilever beam and the piezoelectric ceramics sheet could improve the measuring performance of the shear probe, such as sensitivity and resonance frequency. In this paper, multiobjective optimization algorithm is used to obtain the main design parameters of the shear probe with appropriate sensitivity and resonance frequency. Serial tests are conducted including the tap test and the calibration test to examine the resonance frequency in wet mode, and analyze the sensitivity of the probe, respectively. Soon afterward, the sea trials were carried out in the Western Pacific Ocean. The power spectrum from shear velocity data shows a good agreement with the Nasmyth spectrum. The experiments also testify the validity of the optimal design method of the shear probe.

Multi-AUV coordination in the underwater environment with obstacles

A concept of extended formation which is derived by combining the destination and obstacles in the underwater environment as elements into the traditional formation of AUVs is proposed. In extended formation, an improved potential-field-based approach is introduced to coordinate multiple autonomous underwater vehicles (AUVs). Artificial potential fields which define the control forces are constructed to correspond to a special destination and desired formation geometry. The extended formation with the improved potential fields can be regarded as a multi-body system with closed branches. In the system, the vehicles are interconnected in a configuration by forces derived from the potentials. Feasibility of the proposed approach is validated by using simulation results.

Hydrodynamic shape genealogy for teardrop-shaped Autonomous Underwater Vehicles

More diverse marine tasks and longer range water missions require the hydrodynamic shape, viz. hull shape, of Autonomous Underwater Vehicles (AUVs) for both efficient design and least resistance. Therefore a systematic design for the hydrodynamic shape of AUVs is needed and necessary to meet the various requirements. In the present work, a hierarchical classification for the hull shape of AUVs was proposed according to the shape characteristics of the main hull of AUVs. Focused on the teardrop-shaped AUVs, hydrodynamic drags of a series of hull shapes were computed and analyzed using the computational fluid dynamics (CFD) simulation method with different hull shape parameters and Reynolds numbers (Re). The general mathematical model of volumetric coefficient of hydrodynamic drag and hull shape parameters, i.e., length diameter ratio (L/D), nose length diameter ratio (Ln/D), tail length diameter ratio (Lt/D) and Reynolds number (Re), was established and verified. The present work makes it possible to efficiently design the hull shape with minimum drag.

Dynamic simulation of buoyancy engine of underwater glider based on experimentation

As a key component for underwater gliders, the buoyancy engine plays an important role in the operation of gliders, the performance of which directly affects the monolithic reliability. In this paper, to lower costs of research on the buoyancy engine, a dynamic simulation is established by AMEsim software, in which the performance of the low-pressure boost gear pump and that of the high-pressure hydraulic axial piston pump are analyzed. And based on the simulation results, an experiment is designed to verify validity of the simulation. The method of buoyancy engine simulation in this paper may provide a valuable reference for designers.

Path Planning for Underwater Gliders with Motion Constraints

The underwater glider technology is a promising ocean observing technique. This paper presents path planning for underwater gliders as they travel in the water. The objective is that the underwater glider arrives at the destined depth while avoiding the obstacles in the way. Artificial potential field approach is used in the path planning algorithm, which is featured by adding motion constraints of the underwater glider into path generation.

Design and flight performance of hybrid underwater glider with controllable wings

Hybrid underwater glider combines motion modes of traditional autonomous underwater glider and those of autonomous underwater vehicles. Different motion modes need different flight performance, including flight efficiency, static stability, and maneuverability. Conventional hybrid underwater glider with fixed wings can’t achieve optimal flight performance in one flight mission demanding various motion modes. In this article, controllable wings for hybrid underwater glider Petrel II are designed. Angle of attack, sweep angle, and aspect ratio of controllable wings can be changed to adapt to different motion modes. Kinematics and dynamics models of Petrel II are established based on multibody theory. Motion simulations of Petrel II with different wing configurations are conducted in three motion modes, including glide motion, spiral motion, and horizontal turning motion. The simulation results show the impact of wing parameters on flight performance. Field trials demonstrate that the controllable wings can improve the flight performance.

Heat exchanger layout for a thermal underwater glider

Thermal glider is a new type of underwater glider which harvests its propulsive energy from the thermocline in the ocean. Compared with traditional electric underwater glider, the thermal glider may achieve a much longer duration and range. The heat exchangers on the underwater glider can be mounted above the hull, below the hull, and by the sides of the hull. In this paper, hydrodynamic analysis is conducted for the thermal glider with the three heat exchanger layout designs using computational fluid dynamics. Impact of the layout design on glide efficiency and static stability is investigated, using lift to drag ratio and dimensionless position lever as the evaluation parameters. Result shows that the thermal glider is statically stable with the heat exchangers. The layout of the heat exchangers greatly affects the static stability of the glider, while little influence has been found on the glide efficiency. It is also found that taking glide efficiency and static stability into consideration, the heat exchangers are better mounted below the hull. The result provides theoretical guidance for thermal glider design.

Mechanism design of controllable wings for autonomous underwater gliders

Compared with autonomous underwater gliders (AUGs) with fixed wings, gliders with controllable wings have variable hydrodynamics coefficients to achieve better flight performance. In this paper, relations between flight performance and shapes of wings are analyzed. A combined mechanism which contains two sub-mechanisms is presented. It can achieve three kinds of shape changing motions including wings extending and rotating along two axes. With the method of mechanism synthesis, the second sub-mechanism with two degrees of freedom is designed. Rotation vector algorithm is used to establish kinematics models. Forward and inverse solutions of kinematics are obtained. Working space is analyzed. Results show that working space has good continuity and all bars have reasonable lengths. MATLAB is used in inverse solution and getting the control rules of motors. Motion simulation is carried out by ADAMS. Simulation results show that the variation range of wings length is o to 80mm. The variation range of sweep angle and attack angle is 0 to 70 degrees and 0 to 55 degrees. This design can satisfy needs of controllable AUGs.