Heading control method and experiments for an unmanned wave glider

The control system designing of unmanned wave glider(UWG) is challenging since the control system is weak maneuvering, large time-lag and large disturbance, which is difficult to establish accurate mathematical model. The control system for the "Ocean Rambler" UWG is studied in this work. A heading control method based on S-surface controller is designed. For the "rudder zero drift" problem in trials, an improved S-surface control method based on rudder angle compensation is proposed, which can compensate the adverse effects from environmental forces and installation error. The tank test and sea trial results prove that the proposed control method has favorable control performance, and the feasibility and reliability of the designed control system are also verified.

Unmanned wave glider heading model identification and control by artificial fish swarm algorithm

We introduce the artificial fish swarm algorithm for heading motion model identification and control parameter optimization problems for the“Ocean Rambler”unmanned wave glider(UWG).First,under certain assumptions,the rigid-flexible multi-body system of the UWG was simplified as a rigid system composed of“thruster+float body”,based on which a planar motion model of the UWG was established.Second,we obtained the model parameters using an empirical method combined with parameter identification,which means that some parameters were estimated by the empirical method.In view of the specificity and importance of the heading control,heading model parameters were identified through the artificial fish swarm algorithm based on tank test data,so that we could take full advantage of the limited trial data to factually describe the dynamic characteristics of the system.Based on the established heading motion model,parameters of the heading S-surface controller were optimized using the artificial fish swarm algorithm.Heading motion comparison and maritime control experiments of the“Ocean Rambler”UWG were completed.Tank test results show high precision of heading motion prediction including heading angle and yawing angular velocity.The UWG shows good control performance in tank tests and sea trials.The efficiency of the proposed method is verified.

Optimization of an Underwater Wireless Sensor Network Architecture with Wave Glider as a Mobile Gateway

This paper presents an original probabilistic model of a hybrid underwater wireless sensor network(UWSN),which includes a network of stationary sensors placed on the seabed and a mobile gateway.The mobile gateway is a wave glider that collects data from the underwater network segment and retransmits it to the processing center.The authors consider the joint problem of optimal localization of stationary network nodes and the corresponding model for bypassing reference nodes by a wave glider.The optimality of the network is evaluated according to the criteria of energy efficiency and reliability.The influence of various physical and technical parameters of the network on its energy efficiency and on the lifespan of sensor nodes is analyzed.The analysis is carried out for networks of various scales,depending on the localization of stationary nodes and the model of bypassing the network with a wave glider.As a model example,the simulation of the functional characteristics of the network for a given size of the water area is carried out.It is shown that in the case of a medium-sized water area,the model of“bypassing the perimeter”by a wave glider is practically feasible,energy efficient and reliable for hourly data measurements.In the case of a large water area,the cluster bypass model becomes more efficient.

Impact of Evaporation Duct on Electromagnetic Wave Propagation During a Typhoon

The evaporation duct,a result of evaporation from the ocean,is a region above the sea surface in which radio waves are refracted downward.This duct has strong effects on microwave instruments.Typhoons cause huge anomalies in marine meteorological parameters that influence the evaporation duct distribution and structure,which in turn affects the propagation of electromagnetic(EM)waves.However,EM wave propagation under the typhoon process has seldom been reported.Thus,taking Typhoon Phanfone(201929)as an example,this study uses a dataset from the European Centre for Medium-Range Weather Forecasts,combined with the Naval Atmospheric Vertical Surface Layer Model and the parabolic equation model,to study the evaporation duct’s impact on EM wave propagation during a typhoon.The spatial and temporal path loss distributions reveal that large amounts of EM wave energy are emitted from the evaporation duct when the EM wave passes through a typhoon eye.On average,a typhoon eye causes an approximately 20 dB increase in path loss for EM wave propagation at low antenna height.Furthermore,the effects of a typhoon eye on EM wave propagation at different signal frequencies and antenna heights are studied.The results show that a typhoon has a larger impact on EM wave propagation with low signal frequency and high antenna height.

Analysis of the Dynamic System of Wave Glider with a Towed Body

Mobile observation platforms are widely used in oceanographic and marine resource exploration and other applications. Wave Glider is a mobile platform that can transform wave energy into locomotion power and overcome the bottleneck of low energy supply. Wave Glider has recently been applied to tow underwater sensors fulfilling observation tasks. In this paper, the dynamic system of Wave Glider with a towed body is studied by applying multibody mechanics, and the relevant motion conditions of the system are investigated. Dynamic models of Wave Glider with a towed body and tether are first developed individually and then integrated into a whole model. The numerical method is used to obtain the dynamic responses and assess performance of the towed body pulled by the submerged glider of Wave Glider. The effects of sea state, mass of the towed body, and length of the towed cable are investigated on the basis of simulation results. This work can be used for the design and analysis of Wave Glider-towed body systems.

Validation of NCEP and OAFlux air-sea heat fluxes using observations from a Black Pearl wave glider

Latent and sensible heat fluxes based on observations from a Black Pearl wave glider were estimated along the main stream of the Kuroshio Current from the East China Sea to the east coast of Japan,from December 2018 to January 2019.It is found that the data obtained by the wave glider were comparable to the sea surface temperature data from the Operational Sea Surface Temperature and Sea Ice Analysis and the wind field data from WindSat.The Coupled Ocean Atmosphere Response Experiment 3.0(COARE 3.0)algorithm was used to calculate the change in air-sea turbulent heat flux along the Kuroshio.The averaged latent heat flux(LHF)and sensible heat flux(SHF)were 235 W/m^(2)and 134 W/m^(2),respectively,and the values in the Kuroshio were significant larger than those in the East China Sea.The LHF and SHF obtained from Objectively Analyzed Air-Sea Fluxes for the Global Oceans(OAFlux)were closer to those measured by the wave glider than those obtained from National Centers for Environmental Prediction(NCEP)reanalysis products.The maximum deviation occurred in the East China Sea and the recirculation zone of the Kuroshio(deviation of SHF>200 W/m^(2);deviation of LHF>400 W/m^(2)).This indicates that the NCEP and OAFlux products have large biases in areas with complex circulation.The wave glider has great potential to observe air-sea heat fluxes with a complex circulation structure.

Resistance and Seakeeping Investigation for Optimization of the Floating Hull of Wave Glider

Wave glider is the first unmanned autonomous marine robot to use only the ocean’s endless supply of wave energy for propulsion. Wave glider comprises fin system, tether and float which harvest all of its energy from waves and sun to produce forward thrust. As a consequence of the lack of design information and data for the wave glider, the main aim of the study is using computational fluid dynamics (CFD) to present a method to predict calm water resistance for the floating hull through calculations of 3 different hull forms using the same mesh generation under the same conditions. Calculations are carried out using 3 different mesh sizes for Froude number in the range of 0.10 to 0.40 and compared for accuracy of the solution parameters. Wigley parabolic hull, high speed round bilge form (NPL) and Series 60 have been comparatively investigated in order to estimate the hydrodynamics performance of the hull. The linear seakeeping analysis, coupled heave and pitch motions, roll motion, in irregular waves, with one parameter Bretschneider and JONSWAP spectra. Numerical computations have been performed for motion response predictions of the three hulls which cover wave angles from 0? to 180? at 45? intervals for six different forward speeds from 0 to 4.304 knots using Maxsurf Motion software. The close agreement between the numerical predictions shows the importance of CFD applications in estimating the hydrodynamics performance to design the floating hull and the numerical method is useful in glider design. The fine grid is fit to the calculation and shows the most appropriate results because convergent results are obtained as the mesh size decrease so the fine grid is the one which will be applied for the other hulls. Also it can be observed that the added resistance and the RAOs for NPL hull are less than the other hulls. Therefore from the comparisons, the NPL hull is the optimum hull compared to the other hulls from the resistance and seakeeping point of view.

A comparison of multiplatform wind products in the South China Sea during summer and autumn in 2019

Sea surface wind(SSW)observations from a newly developed“Black Pearl”wave glider,the Chinese-French Oceanography Satellite(CFOSAT),the HY-2A microwave scatterometer,and a recently released high-resolution atmospheric reanalysis(ERA5)are evaluated with respect to in-situ buoy observations(115.46°E,19.85°N)from the South China Sea.Buoy observations from June to November 2019 are used to evaluate the wind estimates from the different platforms.The comparisons show that the HY-2A and CFOSAT scatterometer wind speeds have mean root mean square errors(RMSEs)of approximately 1.6 and 1.6 m/s,respectively,and the corresponding mean wind direction RMSEs are approximately 19°and 17°,which indicates that these satellite retrievals meet the requirements of design engineering missions.The wind speed and wind direction RMSEs of ERA5 are approximately 1.9 m/s and 33°,respectively.The correlation coefficients between the HY-2A,CFOSAT,and ERA5 wind speeds and the buoy observations are 0.86,0.85,and 0.84,respectively,and the corresponding coefficients of the wind direction are 0.98,0.98,and 0.93,respectively,at a 95%confidence level.However,the wind sensor in the wave glider provides relatively poor-quality observations compared with the buoy measurements and has higher wind speed and wind direction RMSEs of 2.9 m/s and 50.1°,respectively.Taylor diagrams are utilized to illustrate comprehensive wind comparisons between the multiplatform observations and buoy observations.The results help identify the basic biases in SSWs among different products and enhance confidence in the future use of SSW data for studies of upper ocean dynamics and climate analysis.Suggestions are also off ered to help improve the design of next-generation wave gliders.

Dynamic modeling of a wave glider

We propose a method to establish a dynamic model for a wave glider, a wave-propelled sea surface vehicle that can make use of wave energy to obtain thrust. The vehicle, composed of a surface float and a submerged glider in sea water, is regarded as a two-particle system. Kane＇s equations are used to establish the dynamic model. To verify the model, the design of a testing prototype is proposed and pool trials are conducted. The speeds of the vehicle under different sea conditions can be computed using the model, which is verified by pool trials. The optimal structure parameters useful for vehicle designs can also be obtained from the model. We illustrate how to build an analytical dynamics model for the wave glider, which is a crucial basis for the vehicle＇s motion control. The dynamics model also provides foundations for an off-line simulation of vehicle performance and the optimization of its mechanical designs.