Buoyancy Control System Research Articles

Wave interaction with a forced floating elastic beam in the presence of porous barriers

The investigation focuses on the wave interaction with a floating finite elastic beam which is subjected to a transient force, in the presence of vertical barriers. The study considers three edge conditions: free edge, simply supported edge, and built-in edge conditions. The frequency-domain solution is obtained using the eigenfunction matching method, which involves dividing the solution into symmetric and antisymmetric parts. In addition, a time-domain analysis is conducted by applying Gaussian forcing at different positions on the beam, employing the Fourier transform for analysis. The vertical force on the beam and the time-dependent deflection of the beam are calculated for various porous parameter and water depths. Observations reveal that a forced beam with barriers of lower porosity exhibits increased deflection in free and simply supported edge beams. Additionally, numerical results have been assessed and verified against existing data. The findings from the combination of a forced floating elastic beam with vertical porous barriers will aid in shaping designs for safeguarding aquatic habitats, buoyancy control systems, wave energy conversion, and various other applications.

Numerical Simulation and Experimental Verification of Phase Change Buoyancy Control System

Phase change buoyancy control systems (PBCS) driven by phase change materials have unique advantages over conventional hydraulically actuated buoyancy control systems, especially in their high adaptability for deep-sea exploration and seamless interaction with humans. Studying the heat transfer process and working mechanism of PBCS is helpful to research the precise control mode of the phase change buoyancy regulation system. In this study, we chose paraffin wax as the phase change material for PBCS. A buoyancy generator for phase change buoyancy regulation is designed and manufactured. By studying the relation between its expansion volume and heating time and heat input, the mathematical model of the volume change of PBCS is established. We obtain the calculation results of the PBCS working process by using the computer-aided software MATLAB. Experimental results show that the theoretical volume expansion velocity and volume expansion rate of paraffin are almost consistent with the experimental results. The mathematical calculation model is available and has a significant reference value for further research on the theoretical basis of the diving depth control of PBCS.

Research on Seawater Hydraulic Internal Ball Gear Pump

With high demands for novel technologies in the marine mechatronic instrumentality and the limitations of the present hydraulic pumps, a novel bidirectional seawater hydraulic internal ball gear pump is proposed to accomplish the function of fluid power transmission and control. The proposed hydraulic pump can be used for hydraulic buoyancy control systems of underwater vehicles and different marine mechatronic equipment. In this paper, the model, the meshing and the flow characteristics of the internal ball gear pump are developed. The radial unbalance force of the pump, leakage, and flow pulsation are also analyzed. The new type of eccentric shaft-hole rotary sealing designed in this paper can eliminate axial leakage and is expected to improve volumetric efficiency, working pressure, and power density. Simulation and experimental results show that: (1) by using the concave/convex ball gears rather than the existing gears, the concave ball gear drives the convex ball ring to rotate, realizing energy transfer and conversion; (2) compared with the water hydraulic internal gear pump, the internal ball gear pump has excellent performance. Experimental results also show that when the speed is 1500 rpm, the maximum operating pressure can reach 7 MPa. At 2 MPa, its volumetric efficiency and flow can reach 75% and 0.189L/min, respectively. The outcomes of this study show that the proposed seawater hydraulic internal ball gear pump is effective and has a lot of potential.

Development and Experiments of an Electrothermal Driven Deep-Sea Buoyancy Control Module.

Due to the extremely high pressures in the deep sea, heavy ballast tanks and pressure compensating hydraulic tanks are typically required to support the operation of classic buoyancy controls. Buoyancy control systems driven by phase-change materials (PCM) have unique advantages over conventional hydraulically actuated buoyancy control systems, including high adaptability for deep-sea exploration and simple, lightweight, and compact structures. Inspired by this, a buoyancy control module (BCM) was designed with flexible material as the shell. Instead of a conventional mechanical system, the device uses an electric heating drive to control buoyancy by heating and cooling the PCM. Based on the principle of pressure compensation, this device can adjust the buoyancy of a small underwater vehicle in a deep-sea high-pressure environment. The BCM successfully adjusts the buoyancy to lift itself up and down in the South China Sea at a depth of 3223 m. The performance of the phase-change BCM to control buoyancy under high pressure is validated by systematic experiments and theoretical analysis. Our work proposes a flexible scheme for the design of a deep-sea phase-change-driven BCM and highlights its potential application in deep-sea micro-mechanical systems, especially soft robots.

Buoyancy Control Device Enabled by Reversible Proton Exchange Membrane Fuel Cells for Fine Depth Control

Abstract Fine buoyancy control is essential for underwater robots to maintain neutral buoyancy despite dynamic changes in environmental conditions. This paper introduces a novel buoyancy control system that uses reversible fuel cells (RFC) as a mass-to-volume engine to change the underwater robots' buoyancy. The RFC uses both the water electrolysis process and fuel cell reaction to produce and consume gases in a flexible bladder for volume change. Unlike conventional actuators such as motors and pistons used in buoyancy control, this mechanism is silent, compact, and energy-efficient. A dynamic model that described the dynamics of the RFC-enabled buoyancy change is presented. Then, a proportional-derivative (PD) controller is designed to position the device at any depth underwater. A prototype device is built to validate the dynamic model and the performance of the feedback controller. Experimental results demonstrate a fine depth control performance with 4 cm accuracy and 90 s settling time. The compact buoyancy design is readily integrable with small underwater robots for fine depth change allowing the robots to save actuation energy.

Structural selection and numerical analysis of disk-underwater glider pressure shell

As a new type of underwater glider with many advantages, the disk-underwater glider has been widely used in recent years. The hydraulic buoyancy control system, the attitude control system and the steering control system must be installed inside the pressure housing, therefore, as for the design of the pressure shell, the minimum weight and the maximum effective volume are the important technical indicators. In order to adapt to the saucer appearance of the glider, the pressure resistant structure designed in this paper is a ball - ring - ring pressure resistant structure. Through the ladder finite element numerical simulation, under the premise of ensuring enough strength and rigidity of the pressure bearing shell, we gradually improve the structure of the pressure hull, in order to achieve the design goal of light weight, enough strength and large volume.

Dynamic Modeling of Passively Draining Structures for Aerial–Aquatic Unmanned Vehicles

In the design of hybrid unmanned aerial and underwater vehicles, buoyancy management and weight are two major factors. Large wing volumes used by unmanned air vehicles to fly efficiently drive vehicle buoyancy up, preventing them from submerging. Heavy active buoyancy control systems can overcome this, but cost weight, energy, and time to transition between underwater operation and flight. An alternative design, consisting of a passively flooding and draining wing, is presented in this paper. Relevant dynamic parameters for a full vehicle dynamic model are identified. A dynamic model of a draining structure is developed and verified experimentally on both a simple cylinder and a full wing structure. With proper tuning, the model captures the salient dynamic behavior of passive draining during vehicle egress. A prototype unmanned aerial and underwater vehicle was built, flown, and used to collect flight test data. The model is used to accurately predict the takeoff performance of the vehicle. As given, the model can be incorporated into a full vehicle dynamic model to aid in the design, simulation, and control of hybrid unmanned aerial and underwater vehicles with passively draining components.

A Compact Autonomous Underwater Vehicle With Cephalopod-Inspired Propulsion

AbstractIn this paper, a bioinspired, compact, cost-effective autonomous underwater vehicle system is presented. Designed to operate in a heterogeneous, multivehicle collaboration hierarchy, the presented vehicle design features 3D printing technology to enable fast fabrication with a complex internal structure. Similar to a previous vehicle prototype, this system generates propulsive forces by expelling unsteady, pulsed jets, inspired by the locomotion of cephalopods and jellyfish. The novel thrusters enable the vehicle to be fully actuated in horizontal plane motions, without sacrificing the low-forward-drag, slender vehicle profile. By successively ingesting water and expelling finite water jets, periodic actuation forces are generated at all possible vehicle velocities, eliminating the need for control surfaces used in many conventional underwater vehicle designs. A semiactive buoyancy control system, inspired by the nautilus, adjusts the vehicle depth by passively allowing water flowing into and actively expelling water out of an internal bladder. A compact embedded system is developed to achieve the control and sensing capabilities necessary for multiagent interactions with the minimum required processing power and at a low energy cost. The new vehicle design also showcases an underwater optical communication system for short-range, high-speed data transmission, supplementing the conventional acoustic communication system. Experimental results show that, with the thruster motors powered at a 60% duty-cycle, the new vehicle is able to achieve a 1/4 zero-radius turn in 3.5 s and one-body-width sway translation in 2.5 s.

Robotic Fish: Design and Characterization of an Interactive iDevice-Controlled Robotic Fish for Informal Science Education

In this article, we present the design, development, and characterization of a biomimetic robotic fish remotely controlled by an iDevice application (app) for use in informal science education. By leveraging robots, biomimicry, and iDevices, we seek to establish an engaging and unique experience for free-choice learners visiting aquariums, zoos, museums, and other public venues. The robotic fish incorporates a three-degree-of-freedom tail along with a combined pitch and buoyancy control system, allowing for high maneuverability in an underwater three-dimensional (3-D) space. The iDevice app implements three modes of control that offer a vividly colored, intuitive, and user-friendly theme to enhance the user experience when controlling the biomimetic robotic fish. In particular, the implemented modes vary in the degree of autonomy of the robotic fish, from fully autonomous to remotely controlled. A series of tests are conducted to assess the performance of the robotic fish and the interactive control modes. Finally, a usability study on elementary school students is performed to learn about students' perception of the platform and the various control modes.

Hovering Control Based on Buoyancy Control Approach for Under-Actuated AUVs

A buoyancy control system was presented to realize the powerless descent/ascent motion for an under-actuated AUV like REMUS. The sea water was injected into or drained out of the pressure water tanks to tunes the residual buoyancy of the vehicle, and the buoyancy control was realized. An engineering hovering control law based on buoyancy control approach was proposed to keep the vehicle hovering at the programmed depth. The injection and drainage instructs were worked out only based on depth data and its difference, so the hovering control system need not additional sensors. The simple and reliable hovering control system was applied to a type of huge under-actuated AUV, and the experiment results show that it is feasible.

Buoyancy Control for Low-Speed Under-Actuated AUVs

An engineering buoyancy control scheme was proposed to compensate the change of residual buoyancy for low-speed under-actuated AUVs. The buoyancy control system is made up of buoyancy controller and two sets of buoyancy control devices include: water tank, sea water pump, valve grouping, pipeline etc. Buoyancy control devices were configured to both head and tail part of the AUV symmetrical to its buoyant center. Depth control algorithm and buoyancy control algorithm were proposed separately. In the process of voyage at a constant depth, the real time speed, pitch angle and depth error were detected to evaluate the residual buoyancy indirectly, and then the real time buoyancy control was executed by pumping the water into or out of the tanks. The buoyancy control scheme was applied to the type of low-speed under-actuated AUV and simulation and experiments results show that the buoyancy control approach and the control laws are feasible and effective.

Bone density in the loggerhead turtle: functional implications for stage specific aquatic habits

AbstractSeveral studies investigated how changes in bone density are related to the evolution of complex buoyancy control systems in aquatic mammals. Very little is known on sea turtles, although this is one of the most ancient tetrapod groups that successfully colonized the marine environments. Here, we investigated for the first time the relationship between bone density and body size in the loggerhead turtle, Caretta caretta, with the aim to elucidate possible functional connections with the species’ aquatic habits. Humeri were extracted from the carcasses of 72 loggerhead turtles ranging in size from 7 to 89 cm (males = 18, females = 44, unknown = 10). Whole bone density was determined by Archimedes’ principle. Sexes exhibited comparable humerus densities (t‐value = 0.49, P > 0.05). Mean humerus density (1.33 g cm−3) was intermediate within the range reported for marine mammals and suggested no extreme specialization towards an either pelagic or benthic lifestyle. Turtle size and humerus density were significantly correlated (Pearson's correlation = 0.638, P < 0.01). Small juveniles had very light bones compared to adults in accordance with their stage specific pelagic diving and foraging behaviour.

1A2-M04 体積変化型浮力調整装置を有する水中ロボットの開発 : マイコンを用いた姿勢および水深制御(水中ロボット・メカトロニクス)

The goal of this paper is to develop a robot control system for an underwater robot with a buoyancy control system based on the spermaceti oil hypothesis. Sperm whales have a spermaceti organ in their head that is filled with spermaceti oil. It is said that sperm whales control their buoyancy by melting or coagulating spermaceti oil. In our previous study, we built a depth control system for an underwater robot with a buoyancy control device using the theory. In this paper, a depth and posture control system was built using a microcomputer, a pressure sensor and inclination sensors and so on. In addition, a prototype robot was built using the system. The buoyancy control devices use a piston and syringe mechanism, and paraffin wax poured the syringe. Nichrome wires and peltire elements heat and cool the paraffin wax. From the result of the experiments using the robot, it is conformed that when a target depth and posture were indicated, the robot moved to the targets.

Better Endurance and Load Capacity: An Improved Design of Manta Ray Robot (RoMan-II)

An improved design of a biomimetic underwater vehicle (RoMan-II) inspired by manta ray is presented in this paper. The design of the prototype and the swimming motion control are discussed. Instead of using rigid multiple degree-of-freedom linkages as fin rays in the first version, six flexible fin rays are adopted to drive two sided fins which generate thrust through flapping motions. Furthermore, in order to save the energy for a long distance cruising, a bio-inspired gliding motion is incorporated onto the motion control of the improved prototype. With a closed-loop buoyancy control system, the vehicle can perform gliding locomotion in water, which reduces the overall energy consumption. The vehicle can also perform pivot turning and backward locomotion without turning its body. It can achieve an average velocity of one body length per second. The vehicle is able to carry various sensors or communication equipments, as the payload capacity is about 4 kg. Initial testing shows that the operation time of the buoyancy body is estimated to about 6 hours for free swimming and 90 hours for a pure gliding. The flapping frequency, flapping amplitude, and the number of waves performed across the fin's chord and wave directions can be independently tuned through the proposed control scheme. In general, the present prototype provides a useful platform to study the ray-like swimming motion in a single or combination mode of flapping, undulation and gliding.

Sink or swim? Bone density as a mechanism for buoyancy control in early cetaceans

Previous analyses have shown that secondarily aquatic tetrapods, including whales, exhibit osteological adaptations to life in water as part of their complex buoyancy control systems. These structural specializations of bone span hyperostosis through osteoporosis. The past 15 years of paleontological effort has provided an unprecedented opportunity to examine the osteological transformation of whales as they make their transition to an obligate aquatic lifestyle over a 10-million-year period. It is hypothesized that whales manifest their osteological specialization in the same manner as extant semiaquatic and fully aquatic mammals. This study presents and analysis of the microstructural features of bone in early and late archaic cetaceans, and in a comparative sample of modern terrestrial, semiaquatic, and aquatic mammals. Bone histology was examined from the ribs of 10 fossilized individuals representing five early cetacean families, including Pakicetidae, Ambulocetidae, Protocetidae, Remintonocetidae, and Basilosauridae. Comparisons were then made with rib histology from nine genera of extant mammals including: Odocoileus (deer), Bos (cow), Equus (horse), Canis (dog), Lutra (river otter), Enhydra (sea otter), Choeropsis (pygmy hippo), Trichechus (sea cow), and Delphinus (dolphin). Results show that the transition from terrestrial, to semiaquatic, to obligate aquatic locomotion in archaeocetes involved a radical shift in bone function achieved by means of profound changes at the microstructural level. A surprising finding was that microstructural change predates gross anatomical shift in archaeocetes associated with swimming. Histological analysis shows that high bone density is an aquatic specialization that provides static buoyancy control (ballast) for animals living in shallow water, while low bone density is associated with dynamic buoyancy control for animals living in deep water. Thus, there was a shift from the typical terrestrial form, to osteopetrosis and pachyosteosclerosis, and then to osteoporosis in the first quarter of cetacean evolutionary history.

2P1-S-008 マッコウクジラの脳油を参考にした浮力調整装置の試作(水中ロボット・メカトロニクス2,生活を支援するロボメカ技術のメガインテグレーション)

2P1-S-008 マッコウクジラの脳油を参考にした浮力調整装置の試作(水中ロボット・メカトロニクス2,生活を支援するロボメカ技術のメガインテグレーション)

Buoyancy Control for an Autonomous Underwater Vehicle

This paper describes an active buoyancy control system for an autonomous underwater vehicle (AUV). The AUV “Tethra” is a shallow-water craft designed for a target application of underwater video surveying and as a general AUV test-bed. The craft is controlled using an enhanced version of Brook's behaviour based Subsumption Architecture. Mission scenarios that might require active buoyancy control have been identified. Active buoyancy control is realised using ballast tanks and compressed air. A secondary emergency controller and an Emergency Buoyancy System (EBS) are also presented. Buoyancy control behaviours have been developed and are incorporated in the craft's autonomous control algorithms.

Submersible holocamera for detection of particle characteristics and motions in the ocean

A submersible holographic camera has been developed for measuring the particle distributions, characteristics and motions within a sample volume in the ocean. Its main purpose is to provide data on the spatial distribution, size, shape, orientation, inter-particle relationships, turbulence, local shear and relative motion due to swimming and sinking of plankton. This battery powered, modular, self-contained system is remotely operated by a PC through fiber optic links. Data from on-board environmental sensors are used to select locations for recording holograms and relating the images to broader scale physical structures. The holocamera also has a buoyancy control system that allows deployment as a neutrally buoyant drifter or in a slow profiling mode. The instrument is currently configured for in-line holography, but it has been designed to be readily adaptable to off-axis holography. The cylindrical sample volume is 6.3 cm in diameter and its length can be varied from 10 to 68 cm. The light source is a pulsed ruby laser chosen predominantly because zooplankton are typically less sensitive to red light. The laser has independent dual flashlamps for maximum flexibility in selecting delay between exposures. About 300 single or multiple exposure holograms can be recorded during a single deployment. Data such as particle size, shape, orientation, distribution in space and velocity are obtained by reconstructing the holograms, scanning them with a video camera equipped with a microscope objective, digitizing the images and analyzing relevant data. Several recent field tests have demonstrated the system reliability and resolution. Particles with sizes as small as 10 μm and details on cell structures of larger particles in the 3–5 μm range could be identified and used for identifying and categorizing the particles. Sample single and double exposure images, the latter for measuring motion, and sample spatial distributions are provided. Methods for mapping the liquid velocity distribution are addressed briefly. Parameters affecting the image resolution and location in space, such as particle density, distance from the film plane and focus are discussed and demonstrated.

Rupture strength and flow rate of Nautilus siphuncular tube

The siphuncular tube is a key component of the buoyancy control and mechanical strength systems in both Nautilus and fossil cephalopods. We measured the rate of hydrostatically induced fluid flow across the tube wall and tube rupture strength of Nautilus pompilius at hydrostatic pressures in the range of 10–85 bars. We found that in fresh, undecayed tubes, rupture occurs at pressures of about 80–85 bars. This is equivalent to the strength of the shell proper and to the depth limit of the live animal. The siphuncular tube is neither markedly stronger, nor weaker, than the shell. Siphuncle rupture strength is constant in the last 20 chambers of the shell despite a strong decrease in the siphuncle strength index (ratio of tube thickness to radius). The notion that strength index gives an accurate indication of tube strength is therefore in error. This suggests that the geometry of the siphuncular tube can not be straightforwardly used as an index of living depth in fossil cephalopods. Rupture occurs at the siphuncle-septum contact. The junction of the tube to its mechanical supports is thus weaker than the tube itself. Measured flow rates are in the range of 1–20 ml/h/chamber. Flow rates increase linearly with applied pressure and in successively larger chambers as a result of size-related variation in surface area and thickness of the tube wall. Rates of osmotic pumping in live animals are up to three orders of magnitude lower than hydrostatically induced flow rates across the siphuncular tubes of empty shells. Pumping capacity of live animals is apparently limited by functional constraints of the osmotic pump rather than by the fluid conductance properties of the tube wall. Living depth in evolving cephalopod lineages may be limited ultimately by physiologic or chemical restrictions of the osmotic pumping mechanism rather than by mechanical strength of the shell or siphuncle.