Cooperative Sampling Path Planning of Underwater Glider Fleet with Simultaneous Launch and Recovery

As low-cost and highly autonomous ocean observation platforms,underwater gliders encounter risks during their launch and recovery,especially when coordinating multi-glider deployments.This work focuses on cooperative path planning of an underwater glider fleet with simultaneous launch and recovery to enhance the autonomy of sampling and reduce deployment risks.Specifically,the gliders collaborate to achieve sampling considering the specified routines of interest.The overall paths to be planned are divided into four rectangular parts with the same starting point,and each glider is assigned a local sampling route.A clipped-oriented line-of-sight algorithm is proposed to ensure the coverage of the desired edges.The pitch angle of the glider is selected as the optimizing parameter to coordinate the overall progress considering the susceptibility of gliders to currents and the randomness of paths produced by complex navigational strategies.Therefore,a multi-actuation deep-Q network algorithm is proposed to ensure simultaneous launch and recovery.Simulation results demonstrate the acceptable effectiveness of the proposed method.

Dynamic Modeling and Motion Simulation for A Winged Hybrid-Driven Underwater Glider

PETREL, a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV （autonomous underwater vehicle）. It can be treated as a multi-rigid-body system with a floating base and a particular hydrodynamic profile. In this paper, theorems on linear and angular momentum are used to establish the dynamic equations of motion of each rigid body and the effect of translational and rotational motion of internal masses on the attitude control are taken into consideration. In addition, due to the unique external shape with fixed wings and deflectable rudders and the dual-drive operation in thrust and glide modes, the approaches of building dynamic model of conventional AUV and hydrodynamic model of submarine are introduced, and the tailored dynamic equations of the hybrid glider are formulated. Moreover, the behaviors of motion in glide and thrust operation are analyzed based on the simulation and the feasibility of the dynamic model is validated by data from lake field trials.

Development and Experiments of the Sea-Wing Underwater Glider

Underwater gliders, which glide through water columns by use of a pair of wings, are efficient long-distance, long-duration marine environment observatory platforms. The Sea-Wing underwater glider, developed by the Shenyang Institute of Automation, CAS, is designed for the application of deep-sea environment variables observation. The system components, the mechanical design, and the control system design of the Sea-Wing underwater glider are described in this paper. The pitch and roll adjusting models are derived based on the mechanical design, and the adjusting capabilities for the pitch and roll are analyzed according to the models. Field experiments have been carried out for validating the gliding motion and the ability of measuring ocean environment variables. Experimental results of the motion performances of the glider are presented.

Parametric Geometric Model and Hydrodynamic Shape Optimization of A Flying-Wing Structure Underwater Glider

Combining high precision numerical analysis methods with optimization algorithms to make a systematic exploration of a design space has become an important topic in the modern design methods. During the design process of an underwater glider＇s flying-wing structure, a surrogate model is introduced to decrease the computation time for a high precision analysis. By these means, the contradiction between precision and efficiency is solved effectively. Based on the parametric geometry modeling, mesh generation and computational fluid dynamics analysis, a surrogate model is constructed by adopting the design of experiment （DOE） theory to solve the multi-objects design optimization problem of the underwater glider. The procedure of a surrogate model construction is presented, and the Gaussian kernel function is specifically discussed. The Particle Swarm Optimization （PSO） algorithm is applied to hydrodynamic design optimization. The hydrodynamic performance of the optimized flying-wing structure underwater glider increases by 9.1%.

Dynamic Modeling and Three-Dimensional Motion Analysis of Underwater Gliders

For consideration of both the eccentric rotatable rigid body and the translational rigid body, the dynamic model of the underwater glider is derived. Dynamical behaviors are also studied based on the model and can be used as the guidance to underwater gliders design. Gibbs function of the underwater glider system is derived first, and then the nonlinear dynamic model is obtained by use of Appell equations. The relationships between dynamic behaviors and design parameters are studied by solving the dynamic model. The spiral motion, swerving motion in three dimensions and the saw-tooth motion of the underwater glider in vertical plane are studied. Lake trials are carried out to validate the dynamic model.

Stability Analysis of Hybrid-Driven Underwater Glider

Hybrid-driven underwater glider is a new type of tmmanned underwater vehicle, which combines the advantages of autonomous underwater vehicles and traditional underwater gliders. The autonomous underwater vehicles have good maneuverability and can travel with a high speed, while the traditional underwater gliders are highlighted by low power consumption, long voyage, long endurance and good stealth characteristics. The hybrid-driven underwater gliders can realize variable motion profiles by their own buoyancy-driven and propeller propulsion systems. Stability of the mechanical system determines the performance of the system. In this paper, the Petrel-II hybrid-driven underwater glider developed by Tianjin University is selected as the research object and the stability of hybrid-driven underwater glider unitedly controlled by buoyancy and propeller has been targeted and evidenced. The dimensionless equations of the hybrid-driven underwater glider are obtained when the propeller is working. Then, the steady speed and steady glide path angle under steady-state motion have also been achieved. The steady-state operating conditions can be calculated when the hybrid-driven underwater glider reaches the desired steady-state motion. And the steady- state operating conditions are relatively conservative at the lower bound of the velocity range compared with the range of the velocity derived from the method of the composite Lyapunov function. By calculating the hydrodynamic coefficients of the Petrel-II hybrid-driven underwater glider, the simulation analysis has been conducted. In addition, the results of the field trials conducted in the South China Sea and the Danjiangkou Reservoir of China have been presented to illustrate the validity of the analysis and simulations.and to show the feasibility of the method of the composite Lyapunov function which verifies the stability of the Petrel-II hybrid-driven underwater glider.

Motion Analysis and Trials of the Deep Sea Hybrid Underwater Glider Petrel-Ⅱ

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.

A Double-Stage Surrogate-Based Shape Optimization Strategy for Blended-Wing-Body Underwater Gliders

In this paper,a Double-stage Surrogate-based Shape Optimization(DSSO)strategy for Blended-Wing-Body Underwater Gliders(BWBUGs)is proposed to reduce the computational cost.In this strategy,a double-stage surrogate model is developed to replace the high-dimensional objective in shape optimization.Specifically,several First-stage Surrogate Models(FSMs)are built for the sectional airfoils,and the second-stage surrogate model is constructed with respect to the outputs of FSMs.Besides,a Multi-start Space Reduction surrogate-based global optimization method is applied to search for the optimum.In order to validate the efficiency of the proposed method,DSSO is first compared with an ordinary One-stage Surrogate-based Optimization strategy by using the same optimization method.Then,the other three popular surrogate-based optimization methods and three heuristic algorithms are utilized to make comparisons.Results indicate that the lift-to-drag ratio of the BWBUG is improved by 9.35%with DSSO,which outperforms the comparison methods.Besides,DSSO reduces more than 50%of the time that other methods used when obtaining the same level of results.Furthermore,some considerations of the proposed strategy are further discussed and some characteristics of DSSO are identified.

Shape Optimization for A Conventional Underwater Glider to Decrease Average Periodic Resistance

As a type of autonomous underwater vehicle(AUV),underwater gliders(UG)are getting increasing attention in ocean exploration.To save energy and satisfy the mission requirements of a longer voyage,shape optimization for UGs has become a key technique and research focus.In this paper,a conventional UG,including its fuselage and hydrofoil,is optimized,which aims to decrease the average resistance in one motion cycle.To operate the optimization progress for the complex object,multiple free form deformation(FFD)volumes are established for geometric parameterization.High-fidelity simulation models are employed for objective function evaluation and gradients calculation.And sequential quadratic programming(SQP)method is adopted as an optimization algorithm.The optimization results show that there exists a UG with symmetrical and non-horizontal hydrofoils that has lower resistance.

Optimal Matching Analysis of Net Buoyancy and Pitching Angle for Underwater Gliders

Control parameter optimization is an efficient way to improve the endurance of underwater gliders(UGs),which influences their gliding efficiency and energy consumption.This paper analyzes the optimal matching between the net buoyancy and the pitching angle and proposes a segmented control strategy of Petrel-L.The optimization of this strategy is established based on the gliding range model of UG,which is solved based on the approximate model,and the variations of the optimal control parameters with the hotel load are obtained.The optimization results indicate that the segmented control strategy can significantly increase the gliding range when the optimal matching between the net buoyancy and the pitching angle is reached,and the increase rate is influenced by the hotel load.The gliding range of the underwater glider can be increased by 10.47%at a hotel load of 0.5 W.The optimal matching analysis adopted in this study can be applied to other UGs to realize endurance improvement.

A hybrid forecasting model for depth-averaged current velocities of underwater gliders

In this paper,we propose a hybrid forecasting model to improve the forecasting accuracy for depth-averaged current velocities(DACVs) of underwater gliders.The hybrid model is based on a discrete wavelet transform(DWT),a deep belief network(DBN),and a least squares support vector machine(LSSVM).The original DACV series are first decomposed into several high-and one low-frequency subseries by DWT.Then,DBN is used for high-frequency component forecasting,and the LSSVM model is adopted for low-frequency subseries.The effectiveness of the proposed model is verified by two groups of DACV data from sea trials in the South China Sea.Based on four general error criteria,the forecast performance of the proposed model is demonstrated.The comparison models include some well-recognized single models and some related hybrid models.The performance of the proposed model outperformed those of the other methods indicated above.

Design,Hydrodynamic Analysis,and Testing of a Bio-inspired Movable Bow Mechanism for the Hybrid-driven Underwater Glider

Hybrid-driven Underwater Glider(HUG)is a new type of underwater vehicle which integrates the functions of an Autonomous Underwater Glider(AUG)and an Autonomous Unmanned Vehicle(AUV).Although HUG has the characteristics of long endurance distance,its maneuverability still has room to be improved.This work introduces a new movement form of the neck of the underwater creature into HUG and proposes a parallel mechanism to adjust the attitude angle and displacement of the HUG’s bow,which can improve the steering maneuverability.Firstly,the influence of bow movement and rotation on the hydrodynamic force and flow field of the whole machine is analyzed by using the Computational Fluid Dynamics(CFD)method.The degree of freedom,attitude control range and movement amount of the Movable Bow Mechanism(MBM)are obtained,and then the design of MBM is completed based on these constraints.Secondly,the kinematic and dynamic models of MBM are established based on the closed vector method and the Lagrange equation,respectively,which are fully verified by comparing the results of simulation in Matlab and Adams software,then a Radial Basis Function(RBF)neural network adaptive sliding mode controller is designed to improve the dynamic response effect of the output parameters of MBM.Finally,a prototype of MBM is manufactured and assembled.The kinematic,dynamics model and controller are verified by experiments,which provides a basis for applying MBM in HUGs.

Nonlinear Control for Autonomous Underwater Glider Motion Based on Inverse System Method

Autonomous underwater gliders are highly effcient,buoyancy-driven,winged autonomous underwater vehicles. Their dynamics are multivariable nonlinear systems. In addition,the gliders are underactuated and diffcult to maneuver,and also dependent on their operational environment. To confront these problems and to design an effective controller,the inverse system method was used to decouple the original system into two independent single variable linear subsystems. The stability of the zero dynamics was analyzed,and an additional closed-loop controller for each linear subsystem was designed by sliding mode control method to form a type of composite controller. Simulation results demonstrate that the derived nonlinear controller is able to cope with the aforementioned problems simultaneously and satisfactorily.

Nonlinear Feedforward and Feedback Control Design for Autonomous Underwater Glider

Underwater gliders are highly efficient,buoyancy-driven,and winged autonomous underwater vehicles.Their dynamics are multivariable nonlinear systems with unstable internal dynamics and thus their motion control is a significant challenge.To improve the inherent efficiency and enhance the behavior of the underwater glider over a wide operating regime,a nonlinear feedforward and feedback controller was developed.The nonlinear feedforward control design is based on a new stable inversion technique which determines a causal and bounded solution for the unstable internal dynamics.The feedback control law was designed by a quadratic optimal control method.Simulation results show that the derived control system is able to deal with nonminimum phase system and successfully achieves the tracking of planned output trajectories from initial to final conditions.Furthermore,the control effort is very low,which means the glider with limited power storage has longer range and higher endurance.

Modeling and Simulation of A Novel Autonomous Underwater Vehicle with Glider and Flapping-Foil Propulsion Capabilities

HAISHEN is a long-ranged and highly maneuverable AUV which has two operating modes： glider mode and flapping-foil propulsion mode. As part of the vehicle development, a three-dimensional mathematical model of the conceptual vehicle was developed on the assumption that HAISHEN has a rigid body with two independently controlled oscillating hydrofoils. A flapping-foil model was developed based on the work done by Georgiades et al. （2009）. Effect of controllable hydrofoils on the vehicle stable motion performance was studied theoretically. Finally, a dynamics simulation of the vehicle in both operating modes is created in this paper. The simulation demonstrates that： （1） in the glider mode, owing to the independent control of the pitch angle of each hydrofoil, HAISHEN travels faster and more efficiently and has a smaller turning radius than conventional fix-winged gliders; （2） in the flapping-foil propulsion mode, HAISHEN has a high maneuverability with a turning radius smaller than 15 m and a forward motion velocity about 1.8 m/s; （3） the vehicle is stable under all expected operating conditions.

CFD approach to modelling, hydrodynamic analysis and motion characteristics of a laboratory underwater glider with experimental results

Underwater gliders are buoyancy propelled vehicle which make use of buoyancy for vertical movement and wings to propel the glider in forward direction.Autonomous underwater gliders are a patented technology and are manufactured and marketed by corporations.In this study,we validate the experimental lift and drag characteristics of a glider from the literature using Computational fluid dynamics(CFD)approach.This approach is then used for the assessment of the steady state characteristics of a laboratory glider designed at Indian Institute of Technology(IIT)Madras.Flow behaviour and lift and drag force distribution at different angles of attack are studied for Reynolds numbers varying from 10^(5) to 10^(6) for NACA0012 wing configurations.The state variables of the glider are the velocity,gliding angle and angle of attack which are simulated by making use of the hydrodynamic drag and lift coefficients obtained from CFD.The effect of the variable buoyancy is examined in terms of the gliding angle,velocity and angle of attack.Laboratory model of glider is developed from the final design asserted by CFD.This model is used for determination of static and dynamic properties of an underwater glider which were validated against an equivalent CAD model and simulation results obtained from equations of motion of glider in vertical plane respectively.In the literature,only empirical approach has been adopted to estimate the hydrodynamic coefficients of the AUG that are required for its trajectory simulation.In this work,a CFD approach has been proposed to estimate the hydrodynamic coefficients and validated with experimental data.A two-mass variable buoyancy engine has been designed and implemented.The equations of motion for this two-mass engine have been obtained by modifying the single mass version of the equations described in the literature.The objectives of the present study are to understand the glider dynamics adopting a CFD approach,fabricate the glider and its variable buoyancy engine and test its trajectory in water and compare it with numerically obtained trajectory in the vertical plane.

Dynamic Model and Motion Characteristics of an Underwater Glider with Manta-inspired Wings

An underwater glider with bionic wings controlled by two operating modes is proposed to perform a variety of marine exploration tasks.The system composition of the vehicle and the structural design of wings inspired by manta ray are presented.The bionic wings can keep outstretched or realize oscillating motions according to the operating modes of the vehicle.A universal dynamic model of the vehicle was derived from multibody theory.Gliding,sailing and steering motions were simulated based on the dynamic model to illustrate the dynamic behaviors of the vehicle under different types of propulsion techniques.The results obtained through simulated calculation are basically consistent with the experimental data,which indicate that the developed dynamic model is applicable to describe the motion characteristics of the vehicle.Experiments were conducted in coastal area to analyze the propulsive characteristics of the bionic wings and sea trials involving multifarious motions were carried out,the applicability of the vehicle in marine environment was verified.

Underwater glider design based on dynamic model analysis and prototype development

Underwater gliders are efficient mobile sensor platforms that can be deployed for months at a time, traveling thousands of kilometers. Here, we describe our development of a coastal 200 m deep underwater glider, which can serve as an ocean observatory platform operating in the East China Sea. Our glider is developed based on dynamic model analysis: steady flight equilibrium analysis gives the varied range of moving mass location for pitch control and the varied vehicle volume for buoyancy control; a stability analysis is made to discuss the relationship between the stability of glider motion and the location of glider wings and rudder by root locus investigation of glider longitudinal- and lateral-directional dynamics, respectively. There is a tradeoff between glider motion stability and control authority according to the specific glider mission requirements. The theoretical analysis provides guidelines for vehicle design, based on which we present the development progress of the Zhejiang University (ZJU) glider. The mechanical, electrical, and software design of the glider is discussed in detail. The performances of glider key functional modules are validated by pressure tests individually; preliminary pool trials of the ZJU glider are also introduced, indicating that our glider functions well in water and can serve as a sensor platform for ocean sampling.

Hydrodynamic analyses of typical underwater gliders

The underwater glider changes its weight and the weight distribution through the battery use, to move up and down and forward in the sea. It enjoys many advantages such as a long endurance, and a long operational range with its unique device. The performance of the underwater glider can not evaluated only by the drag, the energy consumption is also one of the key factors. In this paper, the power conversion ratio is proposed according to the transfer efficiency from the gravitational potential energy to the available work, and the performances of three typical underwater gliders are evaluated from multi-angles, such as the drag, the power conversion ratio and the barycenter＇s offset. So the glide performance and the energy consumption in various motion states can be analyzed. The results of this paper can provide a theoretical basis for further study of underwater gliders.

Design,hydrodynamic analysis,and testing of a bioinspired controllable wing mechanism with multi-locomotion modes for hybrid-driven underwater gliders

Hybrid-driven technology,which can improve the sailing performance of underwater gliders(UGs),has been successfully used in ocean observation.However,a hybrid-driven UG(HUG)with an added tail propeller is still unable to achieve backward and turning motion with a body length radius,and the hydrodynamic pitch moment acting on the HUG that is mainly caused by the fixed-wing makes it difficult to achieve high-precision attitude control during fixed-depth navigation.To solve this problem,a two-degree-of-freedom bioinspired controllable wing mechanism(CWM)is proposed to improve the maneuverability and cruising ability of HUGs.The CWM can realize five motion modes:modifying the dihedral angle or anhedral angle,changing the frontal area of the wing,switching the wing from horizontal to be a vertical rudder,flapping the wing as propulsion,and rotating the wing as a vector propeller.First,the design process of the CWM is provided,and hydrodynamic forces in each motion mode of three CWMs with different trailing edge sweepback angles(TESA)and attitude angles are analyzed through computational fluid dynamics simulation.The relationship between hydrodynamics and the attitude angles or TESA of the CWM is analyzed.Then,experiments are conducted to measure the hydrodynamics of the CWM when it is in a flapping wing mode and rotating the wing as a vector propeller,respectively.The hydrodynamic forces obtained from the simulation are consistent with data measured by a force sensor,proving the credibility of the simulated hydrodynamics.Subsequently,by applying the results of the hydrodynamic force in this study,the flapping trajectory of the wingtip is planned using the cubic spline interpolation method.Furthermore,two underwater demo vehicles with a pair of CWMs are developed,and experiments are conducted in a water tank,further validating and demonstrating the feasibility of the proposed CWM.