System design optimization of an underwater glider involves various disciplines, such as hydrodynamics, structure, sizing, control, power, payload, and trajectory, which overlap with each other and influence the endurance of the system. Compared with traditional optimization methods, multidisciplinary design optimization provides a more efficient method for complex engineering problems involving overlapping disciplines. This article establishes a universal disciplinary framework of an underwater glider after the system analysis, which involves five disciplines, including hydrodynamic shape, pressure hull, buoyancy, attitude, and energy. To decouple the relationship among these disciplines and improve the efficiency of optimization, approximate models in the disciplines of hydrodynamic shape and pressure hull are established. After the coupling analysis, a novel approach is proposed for the system design optimization of an underwater glider, in which the concurrent subspace optimization, penalty function method, and the multipopulation genetic algorithm are combined together. The approach proposed in this article can meet the diversified design requirements of underwater gliders in different observation missions, which is verified by a sea trial of an improved Petrel-L glider.

The deepening of ocean measurement work requires higher transmission bandwidth and information calculation efficiency, which provides an opportunity for fog computing. Compared to cloud computing, fog computing shows distribution because it concentrates data, processing, and application on devices at the edge of the network. In this paper, the Ocean of Things (OoT) framework is designed for marine environment monitoring based on IoT technology. The OoT is divided into three layers, including data acquisition layer, fog layer, and cloud layer. In the fog layer, in order to complete the quality control of the sensor measurement data, we use the numerical gradient based method to process the original acquisition data. And improved D-S algorithm is designed for multi-sensor information fusion, reducing data capacity and improving data quality. In the cloud layer, we build ocean information change models based on fog layer data to predict the dynamic ocean environment. The designed fog layer is evaluated based on marine multi-sensor information. The results have shown that fog-based multi-sensor data processing shows low time consumption and high reliability. Moreover, this paper uses the real temperature datasets to evaluate the prediction accuracy of the cloud model. Finally, we tested the performance of the designed OoT framework with multiple datasets. The simulation results show that the framework can improve the efficiency of data utilization at sea and improve the efficiency of information utilization.

Underwater glider (UG) is the only marine equipment in the field of ocean observation that can realize unmanned autonomous, all-weather and wide-area continuous 3-D observation. The rapid individualized design (RID) and full lifecycle management (FLM) make two difficulties to be solved in the industrialization development of UGs since the UG system involves interdisciplinary multiphysics and there exists multisource uncertainties in complex ocean environment. With the application of new information technologies in industry, the above problems can be effectively solved by the digital twin (DT)-driven methodology. In this article, an architecture of DT-driven RID and FLM for UGs is first put forward based on our previous theoretical research and technique development. Then, the proposed architecture of DT-driven methodology is researched in detail in terms of its digital modeling, design optimization, virtual verification and practical application. Finally, Petrel developed by China is introduced, and a typical preliminary application of DT-driven methodology is presented based on petrel to verify its feasibility. The architecture proposed in this article is also appropriate for other types of autonomous underwater vehicles.

With recent developments in battery technology and low power technology, biofouling, a process referring to the gradual accumulation of organisms on underwater surfaces, has gained a foothold as the primary adversary in long-duration underwater glider flights (C. D. Haldeman, D. K. Aragon, T. Miles, S. M. Glenn, and A. G. Ramos, “Lessening biofouling on long-duration AUV flights: Behavior modifications and lessons learned,” in Proc. OCEANS MTS/IEEE Conf., Monterey, CA, USA, 2016, pp. 1-8). Not only can biofouling increase the drag of the glider, but also it can add the buoyancy discrepancies, which changes the flight characteristics of the glider. Thus, it is necessary to adjust the flight parameters of underwater gliders accordingly for long-duration flights. In this article, the problems of a Petrel-L glider caused by biofouling are introduced. Several critical parameters including the hydrodynamic coefficients, the thermal expansion coefficient, the compressibility, and the net buoyancy compensation of the glider are optimized by an inner penalty function method based on the glider data and the dynamic model of Petrel-L. The effect of these parameters influenced by biofouling on the gliding range is analyzed. The results indicate that the changed hydrodynamic coefficients and net buoyancy compensation decrease the gliding range by 14.64% when the hotel load, including the power of the control system and the sensors, is 0.2 W. The gliding range loss can be decreased to 7.11% by adjusting the flight parameters. This article provides a reference of flight parameter adjustment for other types of biofouled underwater gliders.

A hybrid underwater glider Petrel-II has been developed and field tested. It is equipped with an active buoyancy unit and a compact propeller unit. Its working modes have been expanded to buoyancy driven gliding and propeller driven level-flight, which can make the glider work in strong currents, as well as many other complicated ocean environments. Its maximal gliding speed reaches 1 knot and the propelling speed is up to 3 knots. In this paper, a 3D dynamic model of Petrel-II is derived using linear momentum and angular momentum equations. According to the dynamic model, the spiral motion in the underwater space is simulated for the gliding mode. Similarly the cycle motion on water surface and the depth-keeping motion underwater are simulated for the level-flight mode. These simulations are important to the performance analysis and parameter optimization for the Petrel-II underwater glider. The simulation results show a good agreement with field trials.