Floating Structure with Stabilised Buoyancy Control Device for Photovoltaic Application

Conventional approach of energy derivation is causing anthropogenic pollution and climate change. Various sustainable alternatives of renewable energy particularly solar energy have been developed and implemented as a part of the global effort to gradually decommission usage of fossil fuel and in turn, reduce carbon footprint to overcome adverse environmental impacts. Nevertheless, it was reported that in 2019, only 0.85% of total energy used globally is powered by solar energy. Photovoltaic by itself is not feasible enough due to magnified requirement of land for its installation. Therefore, one of the solutions is floating photovoltaic. However, floating photovoltaic is also restraint by the impact of tidal wave. Characterisation of relationship between stability of large floating structures corresponding to volumetric displacement of the buoyancy control device is the focal point of this paper. Significance of tidal wave impact is empirically assessed based on a scaled-down model of buoyancy control device integrated large floating structure by manipulating the buoyancy of buoyancy control device assisted structure to structure without buoyancy control device under a controlled environment. Fluctuation of the buoyancy control device can be reduced by up to 99.65% when tested against highest configuration of wave transducer by displacing only 50% of air with water. Meanwhile, neutral buoyancy is achieved up to almost 100% when the buoyancy control device is completely filled with water and total submergence has been achieved.

Design of a Depth Control Mechanism for an Anguilliform Swimming Robot

This paper discusses the design and implementation of a depth control mechanism for an anguilliform swimming robot. Researchers analyzed three different methods of controlling the depth of the robot, including out-of-plane thrust direction, use of foil on the head and buoyancy control at the head and tail. It was determined that buoyancy control at the head and tail was the best method for controlling depth and pitch, given typical forward speeds of the robot. Details are given into the design of this mechanism, including a stress analysis on a critical part, as well as the impacts that these modifications have on the required torque of the drive servos.

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

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.

Scuba diving fatalities in Australia 2001 to 2013: Chain of events

Introduction: We aimed to identify the possible chain of events leading to fatal scuba diving incidents in Australia from 2001–2013 to inform appropriate countermeasures. Methods: The National Coronial Information System was searched to identify scuba diving-related deaths from 2001–2013, inclusive. Coronial findings, witness and police reports, medical histories and autopsies, toxicology and equipment reports were scrutinised. These were analysed for predisposing factors, triggers, disabling agents, disabling injuries and causes of death using a validated template. Results: There were 126 known scuba diving fatalities and 189 predisposing factors were identified, the major being health conditions (59; 47%), organisational/training/experience/skills issues (46; 37%), planning shortcomings (29; 23%) and equipment inadequacies (24; 19%). The 138 suspected triggers included environmental (68; 54%), exertion (23; 18%) and gas supply problems (15; 12%) among others. The 121 identified disabling agents included medical-related (48; 38%), ascent-related (21; 17%), poor buoyancy control (18; 14%), gas supply (17; 13%), environmental (13; 10%) and equipment (4; 3%). The main disabling injuries were asphyxia (37%), cardiac (25%) and cerebral arterial gas embolism/pulmonary barotrauma (15%). Conclusions: Chronic medical conditions, predominantly cardiac-related, are a major contributor to diving incidents. Divers with such conditions and/or older divers should undergo thorough fitness-to-dive assessments. Appropriate local knowledge, planning and monitoring are important to minimise the potential for incidents triggered by adverse environmental conditions, most of which involve inexperienced divers. Chain of events analysis should increase understanding of diving incidents and has the potential to reduce morbidity and mortality in divers.

On the fate of sinking diatoms: the transport of active buoyancy-regulating cells in the ocean

Diatoms are one of the most abundant, diverse and ecologically relevant phytoplanktonic group, contributing enormously to global biogeochemical processes like the carbon and silica cycles. This large success has been partly attributed to the mechanical and optical properties of the silica shell (the frustule) that envelops their body. But since they lack motility it is difficult to conceive how they cope with the fast-fluctuating environment they live in and where distributions of resources are very heterogeneous and dynamical. This pinpoints an important but yet poorly understood feature of diatoms physiology: buoyancy regulation that helps them controlling their sinking speed and position in the water column. While buoyancy regulation by light and nutrients availability has been well studied, the effect of hydromechanical stress via fluid shear has been rather overlooked when considering diatoms dynamics. Here, we aim to start filling this gap by first presenting direct experimental evidences for buoyancy control in response to hydro-mechanical stress and then review recent theoretical models where simple couplings between local shear and buoyancy control always result in heterogeneous cell distributions, specific accumulation regions within complex flows and increased sedimentation times to the depths, features of direct ecological relevance. We conclude by suggesting future experiments aiming to unveil such coupling and therefore gain better understanding on the fate of these fascinating microorganisms in their natural habitat. This article is part of the theme issue ‘Stokes at 200 (part 2)’.

Development of Deterministic Artificial Intelligence for Unmanned Underwater Vehicles (UUV)

The major premise of deterministic artificial intelligence (D.A.I.) is to assert deterministic self-awareness statements based in either the physics of the underlying problem or system identification to establish governing differential equations. The key distinction between D.A.I. and ubiquitous stochastic methods for artificial intelligence is the adoption of first principles whenever able (in every instance available). One benefit of applying artificial intelligence principles over ubiquitous methods is the ease of the approach once the re-parameterization is derived, as done here. While the method is deterministic, researchers need only understand linear regression to understand the optimality of both self-awareness and learning. The approach necessitates full (autonomous) expression of a desired trajectory. Inspired by the exponential solution of ordinary differential equations and Euler’s expression of exponential solutions in terms of sinusoidal functions, desired trajectories will be formulated using such functions. Deterministic self-awareness statements, using the autonomous expression of desired trajectories with buoyancy control neglected, are asserted to control underwater vehicles in ideal cases only, while application to real-world deleterious effects is reserved for future study due to the length of this manuscript. In totality, the proposed methodology automates control and learning merely necessitating very simple user inputs, namely desired initial and final states and desired initial and final time, while tuning is eliminated completely.