Ocean Exploration Research Articles

Development of renewable energy system for low power underwater devices

Underwater sensor networks (UWSNs) are an emerging field in the research area as they have potential applications starting from pollution monitoring to defense and ocean exploration. Ocean monitoring is of great importance in marine scientific research. However, battery-operated devices utilized in such systems have limited power and maintenance is difficult. So, devices used underwater suffer from many research challenges and energy issues. Apart from all the problems, harvesting energy underwater is the main limiting factor. Nonrenewable energies come from sources that may not be replenished in our lifetime. Hence, it is very much essential to use renewable energy sources. Ocean has an unlimited amount of energy like wind energy, solar power, and tidal energy. Obtaining sufficient energy is sort of difficult since devices are underwater. Researchers are continuously working on it. Water energy is quite environmentally friendly, and it is a sustainable solution for a secure energy system. This paper implements a renewable energy system using piezoelectric (PZT) sensor, which generates sufficient power for lowpower underwater devices by employing two stage amplifier circuits. Experimental outcome shows the proposed energy harvesting system can generate a maximum voltage of 10.6 V and current of 10.1 mA which is sufficient to run low power underwater device.

Target Detection in Underwater Sensor Networks by Fusion of Active and Passive Measurements

Underwater target detection plays an important role in the ocean exploration. However, the strong noise and weak communication properties of underwater environment make it challenging to achieve the detection task. This paper is concerned with a non-cooperative target detection issue by fusion of active and passive measurements in underwater sensor networks (USNs). The detection procedure is mainly divided into two phases, i.e., local decision and external fusion. For the first phase, the active and passive measurements are both employed to develop a Chi-square test based local decision rule, where the membership functions are conducted to bias the weight of each measurement in accordance with signal reliability. Based on this, we formulate the communication topology of USNs as a two-layer multi-group (2LMG) structure, such that a hybrid Bayesian fusion algorithm is designed in the second phase to fuse the detection decisions from different sensor nodes. It is worth mentioning that, our solution can integrate the active and passive measurements by local decision, and more importantly, it can improve the detection accuracy and reduce the communication load through the 2LMG-based fusion algorithm. Finally, simulation results are performed to validate the effectiveness of our solution in this paper.

Design of Single Legged Hopper Robot in Gazebo

Abstract: Robotics is one of the core areas where the bioinspiration is frequently used to design various engineered morphologies to develop novel behavioral controllers comparable to human being and animals. Research on legged robots has been going on for over a century. The reason behind such sustained interest in legged robots is due to the fact that most of the earth’s land surface is inaccessible to wheeled or tracked systems. Legged animals can, however, be found everywhere. Thus, mankind has been fascinated with the idea of a mobile legged robot that can handle difficult terrain and be useful in the fields of transportation, forestry, agriculture, fire, fighting, hazardous areas, defense (carrying weapons to soldiers, de-mining), police purposes, assistive devices for walking, entertainment (toy production), robotic pets, and ocean and space exploration. Our project is based on one such example, single legged hopper robot a legged locomotive inspired by the jumping mechanism of click beetles. It aims to create a single legged hopper robot in Gazebo. A simulation tool that offers the ability to accurately, and efficiently, simulate populations of robots in complex indoor and outdoor environments. The Robot Operating System (ROS) works best in the LINUX OS, is the software of version Melodic + Gazebo 9, is utilized in the project.

Underwater Image Enhancement using GAN

The process of enhancing the distorted underwater images to clear image is known as Underwater image enhance- ment. Distorted images are the raw underwater images that taken from the deep portion of ocean, river etc by using different cameras. In general underwater images are mainly used in underwater robotics, ocean pasture and environmental monitor- ing, ocean exploration etc. The underwater image enhancement process is done by using underwater image dataset which includes the distorted images (raw underwater images) and the corre- sponding enhanced underwater images. Currently used image enhancement methods cannot provide sufficient satisfaction to the underwater image enhancement. So proposed a new method by using Generative Adversarial Network (GAN), which tries to produce more images from the dataset.

Time of arrival estimation for underwater acoustic signal using multi-feature fusion

Underwater target detection (UTD) is widely applied in ocean exploration. A key issue for the time-of-arrival (ToA)-based UTD algorithm is to localize the first direct path in an underwater multipath channel. However, the conventional Matched Filter (MF) suffers from a deterioration of the estimation accuracy when the direct arrival of the received signal is non-strongest. Therefore, this paper proposes a multi-feature fusion ToA estimation algorithm. First, a multi-decision strategy including the coarse ToA range estimation and the fine ToA estimation is proposed to realize a balance between computational complexity and estimation accuracy. Second, the coarse ToA range estimation is realized by multi-level spectrum analysis. Then, the coarse ToA range is used to localize the fine ToA utilizing the multi-feature fusion ToA estimation. Finally, the simulation and experimental results are provided to validate the proposed ToA estimation algorithm. It clearly shows that without training data, the proposed algorithm can not only deal with the multipath acoustic channel problem but also improve the accuracy of the ToA estimation compared to other algorithms.

Seawater refractive index sensor based on a cascaded double grating structure

Seawater salinity is a critical physical parameter in oceanography, affecting ocean circulation, marine ecosystems, and climate. However, current salinity measurement methods have limitations in terms of efficiency, convenience, and integration. Therefore, the development of advanced salinity measurement technology is crucial for ocean exploration and research. In this study, we designed a high-sensitivity ocean refractive index sensor using the guided-mode resonance, which exhibits superior performance in terms of transmission efficiency (approximately 1), full width at half maximum (0.210 nm), and figure of merit (5675.924). Furthermore, we obtained a set of optimized parameters by conducting a systematic study on the relationship between different structural parameters and resonance wavelength, which significantly improves the performance. Additionally, the variation trend of resonance wavelength with the change of refractive index in seawater was studied, which demonstrates that our optimized scheme achieves highly sensitive seawater salinity measurement with good process tolerance, polarization insensitivity, and a wide wavelength working interval. This high-sensitivity ocean refractive index sensor has great potential for a wide range of applications in future ocean exploration studies, such as ocean environment monitoring, marine ecology management, and oceanographic research.

Strongly coupled fluid–structure interaction analysis of aquatic flapping wings based on flexible multibody dynamics and the modified unsteady vortex lattice method

Because of their superior efficiency and low detectability compared to conventional submarine-shaped vehicles, bionic underwater vehicles such as Mantabot are playing increasingly important roles in ocean exploration. However, current research on manta-inspired robots is limited to structural design and pure hydrodynamics analysis of pectoral fin performance, with other aspects such as hydroelasticity and optimal design of flapping wings rarely addressed. This work presents a novel method for analyzing aquatic flapping wings by coupling flexible multibody dynamics with a modified unsteady vortex lattice method. The flexible multibody system is solved by using the absolute nodal coordinate formulation, and the conventional unsteady vortex lattice method is modified to accommodate dynamic stall. Compactly supported radial basis functions are used to transfer the hydroelastic forces and structural displacements across the interface meshes while satisfying global energy conservation, and a predictor–corrector method is used to stabilize the iteration procedure. Three different experiments are used to validate the flexible multibody dynamics solver, the modified unsteady vortex lattice solver, and the proposed fluid–structure interaction framework, respectively. Finally, the hydroelastic framework is demonstrated for a fin-like wing, and how flexibility and movement affect the flapping wing dynamics is examined. Numerical examples show that reducing the structural stiffness of the aquatic flapping wing within a certain range improves the propulsive efficiency but also reduces the thrust coefficient, and how the stiffness distribution affects the thrust and propulsive efficiency remains consistent over a range of the Strouhal number.

MDNet: A Fusion Generative Adversarial Network for Underwater Image Enhancement

Underwater images are widely used in ocean resource exploration and ocean environment surveillance. However, due to the influence of light attenuation and noise, underwater images usually display degradation phenomena such as blurring and color deviation; an enhancement method is required to make the images more visible. Currently, there are two major approaches for image enhancement: the traditional methods based on physical or non-physical models, and the deep learning method. Inspired by the fusion-based idea, this paper attempts to combine traditional methods with deep learning and proposes a multi-input dense connection generator network (MDNet) for underwater image enhancement. Raw images and processed images are input into the network together, the shallow information is fully utilized by dense connection, and the network is trained in generative and adversarial manner. We also design a multiple loss function to improve the visual quality of the generated images. We conduct both qualitative and quantitative experiments, and then compare the results with state-of-the-art approaches comprehensively using three representative datasets. Results show that the proposed method can effectively improve the perceptual and statistical quality of underwater images.

AUH, a New Technology for Ocean Exploration

The demand for ocean exploration down to the deep seafloor, for instance, ocean resource exploration and ocean observations, has promoted innovations in underwater technology. Underwater unmanned vehicles are urgently required to be deployed and operate on the seafloor. Because most underwater vehicles are unable to operate on the seafloor and even have difficulty reaching there, we developed a seafloor-resident autonomous underwater helicopter (AUH). This paper introduces the new idea and design of AUHs and discusses the pros and cons of AUHs in comparison with other underwater vehicles. Afterwards, we verify the importance of developing new facilities to enable mankind to easily operate close to the seafloor.

A numerical approach for acoustic radiation and scattering of moving bubbles at low frequencies

The acoustic radiation and scattering of underwater bubbles play an important role in ocean exploration, target localization, acoustic measurements, etc. The two-phase fluid flow and moving boundary result in the lack of means to predict the sound field, which limits the exploration of relevant characteristics and mechanisms. The present work is intended to introduce a numerical approach for acoustic radiation and scattering of moving bubbles at low frequencies with CFD-BEM coupling method. The two-phase interface is captured with the volume of fluid scheme and the sound field is solved with the boundary element method. After that, some benchmark problems are solved and the results are compared with data from literatures. Finally, the radiation and scattering of moving bubbles at low frequencies are predicted with our approach. The acoustic radiation pressure of bubbles shows a slight increase trend during deformation. As the ka value increases, both the acoustic directionality of radiation and scattering exhibit main and side lobes, and the scattering energy gradually concentrates in the positive direction of the incident wave. For a moving bubble, its displacement and velocity of moving have a significant impact on the directionality of the scattered sound field. Therefore, the problem of bubble localization can be studied based on directionality shift.

Energy-saving profile optimization for underwater glider sampling: The soft actor critic method

Underwater glider is developed for low-cost oceanic exploration. This work aims to solve the energy optimal yo-yo numbers for underwater glider sampling profiles. Firstly, the motion simulator is developed. By specifying the target sampling paths, the navigational constraint is designed to guide the trajectory and to evaluate the sampling quality. The energy consumption of different numbers of yo-yos is analyzed. The problem framework of profile optimization is developed. To solve the proposed problem, a soft actor critic based method is proposed. The proposed method avoids repetitively optimizing by normalizing the remaining progress of sampling into standard inferring inputs. Through simulations, the results of soft actor critic profile optimization regarding energy consumption and sampling performance are comparable to those of meta-heuristic algorithms and Lipschitz continuity based optimizations. Moreover, the proposed method shows the computational advantages. This work provides a reference to estimate and save the energy consumption of underwater gliders.

Design of OMC-Sagnac Loop Using PDMS and Different Package Structures to Improve Sensing Performance and Optimize the Ill-Conditioned Matrix

In the process of ocean exploration, highly accurate and sensitive measurements of seawater temperature and pressure significantly impact the study of seawater’s physical, chemical, and biological processes. In this paper, three different package structures, V-shape, square-shape, and semicircle-shape, are designed and fabricated, and an optical microfiber coupler combined Sagnac loop (OMCSL) is encapsulated in these structures with polydimethylsiloxane (PDMS). Then, the temperature and pressure response characteristics of the OMCSL, under different package structures, are analyzed by simulation and experiment. The experimental results show that structural change hardly affects temperature sensitivity, and square-shape has the highest pressure sensitivity. In addition, with an input error of 1% F.S., temperature and pressure errors were calculated, which shows that a semicircle-shape structure can increase the angle between lines in the sensitivity matrix method (SMM), and reduce the effect of the input error, thus optimizing the ill-conditioned matrix. Finally, this paper shows that using the machine learning method (MLM) effectively improves demodulation accuracy. In conclusion, this paper proposes to optimize the ill-conditioned matrix problem in SMM demodulation by improving sensitivity with structural optimization, which essentially explains the cause of the large errors for multiparameter cross-sensitivity. In addition, this paper proposes to use the MLM to solve the problem of large errors in the SMM, which provides a new method to solve the problem of the ill-conditioned matrix in SMM demodulation. These have practical implications for engineering an all-optical sensor that can be used for detection in the ocean environment.

Uncrewed surface systems facilitating a new era of global ocean exploration

There is growing recognition that key to addressing critical issues like climate change, global sea level rise and the long-term sustainability of humankind is a more complete understanding of our oceans and processes within them that account for the distribution of global heat, CO2 and provide sustenance to so many. Yet, despite years of effort, less than 25% of the global ocean seafloor has been mapped and less than 5% of the ocean volume explored, likely due to the cost and inefficiency of traditional ocean mapping and exploration techniques using large, very expensive, crewed research vessels. Recent advances in the development of uncrewed surface vessels offer the possibility to reduce costs and increase efficiency of ocean mapping and exploration. Such efficiencies can be gained by using small mother ship-deployed uncrewed vessels acting as relatively inexpensive mapping and sampling force multipliers or the use of small uncrewed vessels launched to from a mother ship to monitor and control autonomous underwater vehicles, allowing multiple operations simultaneously and “verified, directed sampling”, all while freeing the mother ship for independent operations. We are also seeing the development of larger uncrewed vessels launched from shore with long-endurance and range, capable of carrying a full suite of deep ocean mapping and exploration tools. All of these systems and approaches offer great hope but it is very early in our understanding of their full capabilities, costs and limitations and we must be careful not to overpromise, leading to disappointments and early abandonment of a potentially innovative approach, while at the same time maintaining the patience required to continue the research, investment and innovation that will hopefully bring us to a new world of efficient and effective ocean mapping and exploration that will allow us to meet our goal of complete coverage of the ocean.

Reduced venous oxygen depletion in response to at-sea acoustic disturbance in diving northern elephant seals

Marine mammals face increased human activities in the ocean, including shipping, recreation, and seismic exploration. Such disturbances may alter short-term behavior and long-term life history patterns; however, many of the mechanistic details of responses remain unknown. Because marine mammals survival depends on their diving abilities, physiological specializations to diving will likely define the scope of underwater responses to a disturbance. Prior research in aquatic animals has demonstrated an increased bradycardia in response to underwater stressors. We examined cardiovascular physiological responses to disturbances at sea in freely diving juvenile northern elephant seals ( Mirounga angustirostris). We predicted that, after an acoustic disturbance at sea, seals would intensify the dive response, resulting in reduced whole-body oxygen (O 2 ) consumption and slower venous O 2 depletion. To test this hypothesis, we recorded venous P O2 and diving behavior in translocated juvenile northern elephant seals that were exposed to experimental acoustic disturbances while freely diving at sea. Venous P O2 was measured in the extradural vein using a Clark polarographic electrode attached to a biologger. After being exposed to an acoustic noise during the ascent phase of deep dives, seals typically exhibited an immediate inversion of the dive, descending to deeper depths. Dives with acoustic disturbances were significantly longer than dives prior to the acoustic disturbance (24.8 ± 6.2 mins vs 19.1 ± 2.9 mins). Although the magnitude of P O2 depletion was not significantly different between pre-disturbance dives and disturbed dives (52.6 ± 21.6 mmHg vs 53.5 ± 20.8 mmHg, n= 27 paired dives), the depletion rate was slower in disturbed dives. In dives prior to the disturbance, P O2 depletion was 3.2 ± 1.5 mmHg min -1 , but in dives with a disturbance, P O2 depletion was 2.5 ± 1.3 mmHg min -1 . This reduction in venous P O2 depletion rate suggests O 2 consumption during disturbed dives may be similar to the amount consumed during non-disturbed dives. This reduction may be a result of altered perfusion, including reduced muscle blood flow. In particular, reduced perfusion to working muscle would likely reduce O 2 extraction, and may be a key factor in fine-tuning the dive response after a disturbance to conserve O 2 for the brain and heart. National Science Foundation This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Overview of Underwater 3D Reconstruction Technology Based on Optical Images

At present, 3D reconstruction technology is being gradually applied to underwater scenes and has become a hot research direction that is vital to human ocean exploration and development. Due to the rapid development of computer vision in recent years, optical image 3D reconstruction has become the mainstream method. Therefore, this paper focuses on optical image 3D reconstruction methods in the underwater environment. However, due to the wide application of sonar in underwater 3D reconstruction, this paper also introduces and summarizes the underwater 3D reconstruction based on acoustic image and optical–acoustic image fusion methods. First, this paper uses the Citespace software to visually analyze the existing literature of underwater images and intuitively analyze the hotspots and key research directions in this field. Second, the particularity of underwater environments compared with conventional systems is introduced. Two scientific problems are emphasized by engineering problems encountered in optical image reconstruction: underwater image degradation and the calibration of underwater cameras. Then, in the main part of this paper, we focus on the underwater 3D reconstruction methods based on optical images, acoustic images and optical–acoustic image fusion, reviewing the literature and classifying the existing solutions. Finally, potential advancements in this field in the future are considered.

Implication of Freeze-Thaw Erosion and Mechanism Analysis of High-Performance Aromatic Liquid Crystal Fibers.

According to the demand for high-performance fibers for high-latitude ocean exploration and development, this paper selects representative products of high-performance liquid crystal fibers: thermotropic liquid crystal polymer fibers (TLCP) and poly p-phenylene terephthalamide (PPTA) fibers. Through a series of freeze-thaw (F-T) experiments for simulating a real, cold marine environment, we then measure the retention of mechanical properties of these two kinds of fibers. Before that, due to the difference in their chemical structures, we tested their Yang-Laplace contact angle (YLCA) and water absorption; the results suggested that PPTA fibers would absorb more moisture. Surprisingly, then, compared with thermotropic liquid crystal polymer (TLCP) fibers, the retention of the mechanical properties of poly p-phenylene terephthalamide (PPTA) fibers decreased by around 25% after the F-T experiments. The Fourier-transformed infrared (FT-IR) analysis, the attenuated total reflection (ATR) accessory analysis and the degree of crystal orientation measured by two-dimensional wide-angle X-ray diffraction (2D-WAXD) confirm that no changes in the chemical and the orientation structure of the crystal region of the fibers occurred after they underwent the F-T cycles. However, as observed by scanning electron microscopy (SEM), there are microcracks of various extents on the surface of the PPTA fibers, but they do not appear on the surface of TLCP fibers. It is obvious that these microcracks will lead to the loss of mechanical properties; we infer that the moisture absorbed by the PPTA fibers freezes below the freezing point, and the volume expansion of the ice causes the collapse of the microfibrillar structure. The two sorts of fibers subjected to the F-T experiments are immersed in a sodium chloride solution, and the amount of water infiltrated into the PPTA microfibrillar structure is evaluated according to the content of sodium ions in the fiber surface and subsurface layers through X-ray spectroscopy (EDS) elemental analysis. From the above analysis, we found that TLCP fibers can more effectively meet the operating standards of the severe and cold marine environment.

Model Identification and Control of a Buoyancy Change Device

There are several compelling reasons for exploring the ocean, for instance, the potential for accessing valuable resources, such as energy and minerals; establishing sovereignty; and addressing environmental issues. As a result, the scientific community has increasingly focused on the use of autonomous underwater vehicles (AUVs) for ocean exploration. Recent research has demonstrated that buoyancy change modules can greatly enhance the energy efficiency of these vehicles. However, the literature is scarce regarding the dynamic models of the vertical motion of buoyancy change modules. It is therefore difficult to develop adequate depth controllers, as this is a very complex task to perform in situ. The focus of this paper is to develop simplified linear models for a buoyancy change module that was previously designed by the authors. These models are experimentally identified and used to fine-tune depth controllers. Experimental results demonstrate that the controllers perform well, achieving a virtual zero steady-state error with satisfactory dynamic characteristics.

High‐Responsivity Natural‐Electrolyte Undersea Photoelectrochemical Photodetector with Self‐Powered Cu@GaN Nanowires Network

AbstractUndersea optical communication (UOC) has been considered as the most potential next‐generation underwater wireless communication technology for ocean exploration. Photodetector is the essential component in UOC system, however, the harsh undersea environment like light attenuation and seawater corrosivity restricts the applications of conventional photodetectors. Herein, a novel natural‐electrolyte self‐powered photoelectrochemical (PEC) photodetector based on core‐shell structured Cu@GaN nanowires (NWs) network is demonstrated and direct utilization of seawater. High quality GaN shell is encapsulated on the Cu NWs network through Ga‐coating and high temperature nitridation processes. A Schottky junction along radial direction has formed at the Cu/GaN interface due to the outward diffusion of Cu into the GaN layer. Such a structure provides narrowed band detection on blue light as well as efficient carrier separation. A self‐powered undersea PEC photodetector is designed with a mini‐pipes connected device chamber, which allows direct indrawing of seawater and blue channel light communication (458 nm). This photodetector works stably for UOC in both shallow and deep‐sea conditions in Pacific Ocean area. It shows a high responsivity up to 5.04 mA W−1 and rapid response time of 0.68 ms. This photodetector can be easily integrated to marine equipment without waterproof packaging for the future energy‐saving UOC.

Design of a novel energy harvesting mechanism for underwater gliders using thermal buoyancy engines

Underwater gliders (UGs) are becoming popular in ocean exploration. However, the main limitation for their development is their supply of energy. This paper proposes a novel energy harvesting mechanism for an underwater glider equipped with a thermal buoyancy engine. The thermal buoyancy engine changes the buoyancy of the glider, due to the difference of temperature of the ocean, and it drives the glider up and down in the water. These manoeuvres drive a turbine behind to harvest energy. Based on this harvesting mechanism, first, a new type of thermal buoyancy engine with high ballast capacity is presented. Secondly, a dedicated turbine, mounted behind the glider, is optimally designed based on the Blade Element Momentum Theory (BEMT). In order to consider the un-uniform inflow generated by the wake of the glider, an upgraded version of the BEMT model has been developed. With the results obtained in this paper, enhanced energy efficiency for a self-sustainable underwater glider can be achievable.

A vortex-induction underwater energy harvester based on Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal macro-fiber composites

Various wireless sensors in the Internet of Things (IoT) systems have been adopted in ocean exploration, with increasing energy supply concern. Regarding the marine environment, self-powered sensors utilizing ambient flow and wave energy can increase maintainability with a long lifespan. However, the current underwater piezoelectric energy harvesters made of piezoelectric ceramics suffer from low power density (<0.5 mW cm−3 m−1 s). In this paper, we proposed a vortex-induction underwater piezoelectric energy harvester based on a Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystal macro-fiber composite (MFC). The single crystal MFC shows mechanical flexibility in which the volume fraction of the piezoelectric phase is 70%. Regarding the structure design, a bicylinder configuration with a ladder-shaped cantilever is employed for decreasing the resonant frequency of the underwater piezoelectric energy harvester and enhancing vortex force during fluid–structure interaction process. The designed underwater energy harvester exhibits a high output voltage of 54 Vpp at 0.9 m/s flow in the designed underwater energy harvesting test platform. Due to the high figure-of-merit d 32 × g 32 (7.65 × 10−11 m2/N) of the single crystal, the maximum output power reaches 62 μW under the flow speed of 0.9 m/s. The normalized power density is 1.1 mW cm−3 m−1 s, being 2.3 times larger than that of the state-of-the-art PZT ceramics-based underwater energy harvester. This work will help to mitigate the energy crisis of the IoT system, promoting the development of underwater equipment.