Changes In Buoyancy Research Articles

Buoyancy and vertical distribution of haddock (Melanogrammus aeglefinus) eggs during embryonic development: A comparison with cod (Gadus morhua)

AbstractVertical egg distributions are needed knowledge for understanding exposure to physical forcing, predation pressure, and modelling initial transport from the spawning areas. Egg density and size are the biotic factors determining vertical distributions while the ambient salinity and turbulent mixing are the physical factors contributing to their vertical distributions. Egg buoyancies and densities of Atlantic cod (Gadus morhua) have been extensively studied, while limited information on haddock (Melanogrammus aeglefinus) egg density is available. This is the first comprehensive study on haddock egg densities in Norwegian waters. Eggs were collected from pairs of spawning fish caught at the coast of western Norway and inserted into a density gradient column where density was measured. The haddock eggs were neutrally buoyant at salinities ranging from 28.5 to 31. The density changed during egg development, and the results from the measurements were used to model the vertical distribution of the eggs. The simulations showed that the changes in buoyancy substantially affected vertical distributions. A comparison to previously published data on cod eggs showed that haddock eggs are considerably more buoyant than the cod eggs and are—particularly during calm wind conditions—confined to the surface layer to a larger extent than the cod eggs. The more buoyant attribute of the haddock eggs, together with the lipophilic surface of the egg membrane, is suggested to make haddock eggs more vulnerable to buoyant pollutants, like hydrocarbons.

GASTRIC POLYPOID HYPERPLASIA IN MORAY EELS (MURAENIDAE): EIGHT CASES.

Gastric and intestinal mucosal hyperplasia and polyps are identified as a cause of morbidity and mortality in moray eels. This report describes the clinical presentations, diagnostic procedures, and therapeutic interventions in eight moray eels diagnosed with gastric polypoid hyperplasia. All described cases were humanely euthanized or found deceased, and multifocal adenomatous hyperplasia and polyps extending from the gastric mucosal epithelium were identified in all cases. The moray eels diagnosed with adenomatous hyperplasia and polyps often exhibited anorexia, regurgitation, and occasional changes in buoyancy, and supportive care was unsuccessful in alleviating or resolving these signs.

A method for evaluating safety reliability of descend/ascend drop-weight system and mission abort decision for deep-ocean scientific human submersibles

Descend and ascend of deep-water human-occupied submersibles based on buoyancy changes are enabled using a denomination of dispensable drop-weights, and loss of buoyancy are managed using emergency drop-weights and jettisoning identified systems. Failing to release the drop weights or jettison results in submersible stranding on the sea floor, leads to emergency recovery, and hence the drop-weight configuration has to be highly reliable. The paper, for the first time, based on hydrostatic stability, descend/ascend velocity needs, ocean salinity profile and loss-of-buoyancy situations, proposes a novel on-demand reliability based methodology for determining the safe drop-weight configuration and degradation-based mission abort strategy for deep-ocean human submersibles. Probabilistic on-demand reliability analysis based on IEC61508 standards for safety–critical systems using component field-failure data is carried out and the drop-weight configuration essential to meet the human-rated safety integrity level 3 during all stages of the subsea mission is identified for the deep-ocean human scientific submersible Matsya6000, based on which a mission abort protocol is evolved.

Experimental and numerical study of structural parameters on the heat transfer performance of submerged cooling system

Immersion direct contact cooling effectively transfers heat from electronic components to a cooling solution without additional thermal resistance, due to its high energy density, low power consumption, system simplicity, and integrated thermal management for electronic devices. Current scholarly research on immersed structures predominantly focuses on surface temperature effects, with a scant investigation into internal flow and temperature field distributions concerning boundary layers. This study addresses structural optimization in immersion cooling systems, employing experimental and simulation methods to elucidate the thermal mechanisms by which structural optimization impacts the performance of chip immersion cooling systems. The research examines the impact of panel spacing and liquid level height on the thickness of velocity and thermal boundary layers, as well as the combined effects of natural and forced convection under three distinct cooling modes. Analysis reveals that heat pipe immersion cooling can reduce the heat source junction temperature to 40.7 °C under a 60 W power dissipation, a 47.2 % decrease from the bare heat source temperature. Reducing panel spacing disrupts the thermal boundary, enhancing forced convection and lowering the junction temperature by up to 10.1 % (6.5 °C). As liquid level height increases, the junction temperature initially decreases and then rises, with an optimal height of 175 mm for the best overall heat transfer effect. At low flow velocities (0.04 m/s), the vertical buoyancy-induced flow velocity at the heat source surface (24.2 × 10-6 m/s) exceeds the horizontal forced convection velocity (0.78 × 10-6 m/s), indicating that buoyancy changes due to density differences are significant and must be considered.

External airbag-type deepwater electrodynamic transducer.

An external airbag-type electrodynamic transducer structure was proposed to solve the problems of traditional electrodynamic transducers, such as limited operating depth, failure to work for a long time, and excessive buoyancy change. The driving vibrator of the transducer was placed in the oil-filled cavity to balance the hydrostatic pressure and increase the heat dissipation channel of the coil. The external sound insulation airbag was used to eliminate the dipole's acoustic radiation mode to improve the transducer's acoustic radiation ability. This study analyzed the acoustic radiation performance of the transducer and the influencing law of operating depth on the acoustic radiation performance based on an equivalent circuit containing the acoustic parameters of the airbag. Moreover, the heat dissipation capabilities of the new and old electrodynamic transducer structures were compared through thermal simulation analysis. Then, two experimental prototypes of new and old electrodynamic transducers were fabricated. The source-level test results show that, within the core operating frequency band, the two electrodynamic transducers exhibit equivalent acoustic radiation performance. The external airbag-type electrodynamic transducer has long-time deepwater operation ability, and the buoyancy change can be controlled within an acceptable range of autonomous underwater vehicle thanks to the small airbag.

Evaluation of the mechanisms acting on the Atlantic Meridional Overturning Circulation in CESM2 for the 1pctCO2 experiment

The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the Earth's climate system due to its fundamental role in heat distribution, carbon and oxygen transport, and the weather. Other climate components, such as the atmosphere and sea ice, influence the AMOC. Evaluating the physical mechanisms of those interactions is paramount to increasing knowledge about AMOC's functioning. In this study, the authors used outputs from the Community Earth System Model version 2 and observational data to investigate changes in the AMOC and the associated physical processes. Two DECK experiments were evaluated: piControl and 1pctCO2 , with an annual increase of 1% of atmospheric CO2 . The analysis revealed a significant decrease in the AMOC, associated with changes in mixed layer depth and buoyancy in high latitudes of the North Atlantic, resulting in the shutdown of deep convection and potentially affecting the formation of North Atlantic Deep Water and Antarctic Bottom Water. A vital aspect observed in this study is the association between increased runoff and reduced water evaporation, giving rise to a positive feedback process. Consequently, the rates of freshwater spreading have intensified during this period, which could lead to an accelerated disruption of the AMOC beyond the projections of existing models.

Southern Ocean circulation’s impact on atmospheric CO2 concentration

In the context of past and present climate change, the Southern Ocean (SO) has been identified as a crucial region modulating the concentration of atmospheric CO2. The sustained upwelling of carbon-rich deep waters and inefficient nutrient utilization at the surface of the SO leads to an outgassing of natural CO2, while anthropogenic CO2 is entrained to depth during the formation of Antarctic Bottom water (AABW), Antarctic intermediate water (AAIW) and sub-Antarctic mode water (SAMW). Changes to the SO circulation resulting from both dynamic and buoyancy forcing can alter the rate of upwelling as well as formation and subsequent transport of AABW, AAIW and SAMW, thus impacting the air-sea CO2 exchange in the SO. Models of all complexity robustly show that stronger southern hemispheric (SH) westerlies enhance SO upwelling, thus leading to stronger natural CO2 outgassing, with a sensitivity of 0.13 GtC/yr for a 10% increase in SH westerly windstress. While the impact of changes in the position of the SH westerly winds was previously unclear, recent simulations with high-resolution ocean/sea-ice/carbon cycle models show that a poleward shift of the SH westerlies also enhances natural CO2 outgassing with a sensitivity of 0.08GtC/yr for a 5° poleward shift. While enhanced AABW transport reduces deep ocean natural DIC concentration and increases surface natural DIC concentration, it acts on a multi-decadal timescale. Future work should better constrain both the natural and anthropogenic carbon cycle response to changes in AABW and the compound impacts of dynamic and buoyancy changes on the SO marine carbon cycle.

선박 전복 사례를 통한 부체의 안정 공식 개선 방안

In this research, we initially sought to apply the 'floating body stability equation' traditionally taught in hydrostatics to analyze the stability conditions of a vessel. However, we found that the existing equation was inadequate for interpreting situations where a vessel has capsized. Consequently, this study developed an improved equation by eliminating some unrealistic assumptions and incorporating the phenomenon of increased buoyancy width when the boat tilts. We compared the 'floating body stability equation' with this enhanced version, focusing on tilt angles and buoyancy changes. The improved equation indicates capsizing at tilt angles exceeding 23°, a significant revision from the original equation which deemed angles up to 45° as safe. Although the revised equation seems more reflective of real-world conditions, it is based on a single case study with a simple cuboid boat, so further tests and verification are needed for broader applicability.

Compensating transport trends in the Drake Passage frontal regions yield no acceleration in net transport

Although the westerly winds that drive the Antarctic Circumpolar Current (ACC) have increased over the past several decades, the ACC response remains an open question. Here we use a 15-year time series of concurrent upper-ocean temperature, salinity, and ocean velocity with high spatial resolution across Drake Passage to analyze whether the net Drake Passage transport has accelerated in the last 15 years. We find that, although the net Drake Passage transport relative to 760 m shows insignificant acceleration, the net transport trend comprises compensating trends across the ACC frontal regions. Our results show an increase in the mesoscale eddy activity between the fronts consistent with buoyancy changes in the fronts and with an eddy saturation state. Furthermore, the increased eddy activity may play a role in redistributing momentum across the ACC frontal regions. The increase in eddy activity is expected to intensify the eddy-driven upwelling of deep warm waters around Antarctica, which has significant implications for ice-melting, sea level rise, and global climate.

Design and modeling of an electro-hydraulic buoyancy adjustment actuator

A lightweight, simple-structured, and fast-response buoyancy adjustment actuator is essential for underwater vehicles. This article presents the design of an electro-hydraulic actuator that can adjust buoyancy by electric stimuli. The buoyancy adjustment approach of the actuator resembles that of the swim bladder, but the electrostatic force, instead of the muscle tension, is applied to expand the volume of the actuator so that the buoyancy changes with the volume when the entire weight of the actuator is fixed. We propose the structural design guidelines and the operating constraints of the actuator by investigating its mechanical model via the minimum energy principle. In the experiment, the actuator shows a maximum 8.58 g buoyancy adjustment ability with a self-weight of 58.6 g. The experimental results also demonstrate that the depth of the actuator in water can be controlled by applying different voltage signals. The electro-hydraulic actuator presents promising potential for future underwater intelligent vehicles in adjusting buoyancy and depth control.

Quantifying Self-Noise of the Seaglider AUV Using a Passive Acoustic Monitor

Abstract The Seaglider, a type of underwater glider, is a relatively quiet vehicle in comparison with propelled autonomous underwater vehicles, making it a desirable acoustic receiving platform. Vehicle operations, such as pumping/bleeding oil to change buoyancy, shifting/rotating the battery to change pitch/roll, and oceanographic data collection, do, however, produce some self-noise. This system performance study analyzes the prevalence, frequency content, duration, and levels of self-noise associated with vehicle operations using data collected with a passive acoustic monitoring system mounted on the body of a Seaglider vehicle. Guidance and control functions, including pitch, roll, and buoyancy changes, were the major source of platform noise, producing broadband noise ranging from less than a second to over 3 min in duration, with sound pressure levels of 120‐145.5 dB re 1μPa. Frequencies below 10 kHz were the most impacted by self-noise, with a maximum 1/3 octave level of 137.5 dB re 1μPa in the 2.5kHz band caused by the pumping of oil in the variable buoyancy device. Guidance and control changes occurred during 4%‐13% of the dive for dives greater than 500 m. The bulk of these operations, however, were performed near the surface and apogee of the dive and typically affected only about 6% of the dive cycle duration for deep dives.

How can dugongs (Dugong dugon) travel along the water column at low energetic cost? A novel hypothesis

Dugongs (Dugong dugon) spend most of their lifetime either travelling between the sea surface and shallow seafloors where they forage seagrass beds or swimming just below the sea surface. Observations indicate that these movements are carried out with a very limited or even without swimming activity. We propose the novel hypothesis that dugongs travel along the water column at low energetic cost by taking advantage of the compression of their gas-filled organs by depth-varying water pressure. This hypothesis was formulated in terms of physics as the problem of the vertical displacement through a fluid of a body, which buoyancy is related to the hydrostatic pressure. In absence of the required field measurements to solve this problem, both the total volume and the compressible volume of dugongs were modelled and approximations for their weights found in the literature were used. We examined the cases of slightly positively buoyant bodies at the sea surface that becomes neutrally buoyant just below the surface. The predicted duration of free sinking was consistent with field measurements. The energetic expenditure required to travel back from the seafloor to the surface was assessed. We found that the depths where the dugongs forage the most frequently, corresponded to where the changes in buoyancy due to the hydrostatic pressure only, were moderate.

Study on second-order buoyancy segment linearity in magnetic liquids

The study of second-order buoyancy is important for magnetic fluid applications, particularly for magnetic liquid sensors. Previous research focused solely on the second-order buoyancy change of the permanent magnet, without examining the state of the magnetic liquid or delving deeper into the reasons for the buoyancy change. This paper not only summarizes the laws governing the second-order buoyancy curve, but also employs a two-dimensional simulation model that includes the magnetic liquid in COMSOL Multiphysics software. Through simulation and experimental results, we demonstrate that the second-order buoyancy acting on the permanent magnet in the magnetic fluid produces a segmented linear curve in relation to the distance between the magnet and the container wall. By combining simulation results with theoretical calculations, we explain the segmented linear relationship between the second-order buoyancy and the axial movement of the permanent magnet as resulting from changes in the pressure gradient of the magnetic fluid near the permanent magnet.

EXPERIMENTAL STUDY OF A VARIABLE BUOYANCY SYSTEM FOR LOW DEPTH OPERATION

Autonomous Underwater Vehicles (AUVs) are used for the underwater survey both in coastal areas and deep sea without any human intervention during their operations. However, high energy consumptions required by the thrusters of the AUV’s adversely affect their performance such as range and endurance, etc. Herein, we have presented a novel design and development of a standalone variable buoyancy system for autonomous underwater vehicle and investigated the numerical and experimental analysis of Variable Buoyancy System (VBS) in standalone mode. Design idea is based upon the ‘Pump Driven Variable Buoyancy System (PDVBS)’ using ‘Water Hydraulic Variable Buoyancy System (WHVBS)’ method to control the buoyancy using a diaphragm type positive displacement pump (PDP) with capacity of the maximum buoyancy change rate of 4.5 kg/min. Detail experimental and simulation performance of the developed VBS has been investigated. Developed VBS is tested for maximum depth of 5 m and compared the performance of the experimental and simulation results. Presented results demonstrate that designed VBS is effective in changing buoyancy and controlling heave velocities and that will result to achieve the higher range and endurance and better performance in rescue/attack operations.

Cerebral Venous Thrombosis Combined with Spontaneous Intracranial Hypotension: A Case Report and Review of the Literature

Several cases of cerebral venous thrombosis (CVT) due to spontaneous intracranial hypotension (SIH) have been reported, with an estimated occurrence rate of 1–2% among patients with decreased intracranial pressure. However, the causal relationship between SIH and CVT as a potential risk factor is not well understood. According to the Monro-Kellie principle, this is thought to be caused by compensatory expansion of the cerebral venous system, damage to the intravenous wall due to changes in cerebral buoyancy, or increased venous blood viscosity. Although anticoagulation therapy is typically the first choice of treatment for patients diagnosed with CVT, considering the potential risk of intracerebral hemorrhage in patients with CVT secondary to SIH is important. We report the case of a patient who developed CVT as a complication of SIH and discuss its mechanisms and treatment options. Early identification and appropriate treatment can lead to successful outcomes and the prevention of potential complications.

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.

Modeling carbon export mediated by biofouled microplastics in the Mediterranean Sea

AbstractMarine microplastics can be colonized by biofouling microbial organisms, leading to a decrease in microplastics' buoyancy. The sinking of biofouled microplastics could therefore represent a novel carbon export pathway within the ocean carbon cycle. Here, we model how microplastics are biofouled by diatoms, their consequent vertical motion due to buoyancy changes, and the interactions between particle‐attached diatoms and carbon pools within the water column. We initialize our Lagrangian framework with biogeochemical data from NEMO‐MEDUSA‐2.0 and estimate the amount of organic carbon exported below 100 m depth starting from different surface concentrations of 1‐mm microplastics. We focus on the Mediterranean Sea that is characterized by some of the world's highest microplastics concentrations and is a hotspot for biogeochemical changes induced by rising atmospheric carbon dioxide levels. Our results show that the carbon export caused by sinking biofouled microplastics is proportional to the concentration of microplastics in the sea surface layer, at least at modeled concentrations. We estimate that, while current concentrations of microplastics can modify the natural biological carbon export by < 1%, future concentrations projected under business‐as‐usual pollution scenarios may lead to carbon exports up to 5% larger than the baseline (1998–2012) by 2050. Areas characterized by high primary productivity, that is, the Western and Central Mediterranean, are those where microplastics‐mediated carbon export results to be the highest. While highlighting the potential and quantitatively limited occurrence of this phenomenon in the Mediterranean Sea, our results call for further investigation of a microplastics‐related carbon export pathway in the global ocean.

Study on the Changes in Physical Properties and Buoyancy of Eco-friendly Buoys according to the Mixing of Reprocessed HDPE

Study on the Changes in Physical Properties and Buoyancy of Eco-friendly Buoys according to the Mixing of Reprocessed HDPE

Deglacial change of Antarctic Bottom Water in transient simulations

The deglacial change of Antarctic Bottom Water (AABW) since the Last Glacial Maximum (LGM) was investigated using transient simulations of climate evolution forced by individual deglacial forcings. The TraCE21k simulation faithfully reproduces the ∼500 m deepening of the cell interface between AABW and North Atlantic Deep Water (NADW) and suggests an approximate 1.5 Sv (1 Sv 106 m3 s−1) weakening in the deep Atlantic AABW from the LGM to the modern state. The deglacial Atlantic AABW change is approximately the combined impacts of increasing greenhouse gases and retreating ice sheets. The Southern Ocean sea-ice melting induced by deglacial warming serves as a major controlling factor for both AABW intensity and geometry. Increased surface buoyancy flux associated with reduced brine release leads to a suppressed deep convection over the Weddell Sea and reduced AABW, while the retreat of permanent sea ice favors a deepening of the cell interface. The buoyancy change in the Southern Ocean may also have modulated the deglacial NADW change from an adiabatic overturning perspective.摘要本文利用气候瞬变模拟试验TraCE21k分析了末次冰消期南极底层水 (Antarctic Bottom Water, AABW) 的演变特征及物理机制. TraCE21k的全强迫试验复现了观测记录里现代大西洋AABW相对于冰期时变薄的特征, 其强迫敏感性试验进一步指出冰期-现代AABW的差异主要由大气温室气体的升高及大陆冰川的退缩二者共同驱动. 冰消期气候强迫下海洋和大气温度升高, 南大洋海冰逐渐消融, 后者直接调控了AABW强度和形态的演变. 本文还从绝热翻转环流的观点出发, 认为冰消期南大洋的气候变化潜在影响了北大西洋深层水的演变.

Experimental analysis on the interaction between underground structures and sand layer under groundwater level change

Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures. Global warming and active underground construction cause conspicuous changes in the groundwater level, which further leaves an impact on the underground structures’ serviceability. To reveal the interaction between underground structure and soil under groundwater level change in the sand layer, model tests of circular transportation tunnel and rectangular utility tunnel were carried out. With the self-designed experimental equipment and innovative experimental methods, the changes in tunnel stress, bending moment, buoyancy, and vertical displacement of the rise and drawdown of the groundwater level in the sand layer were studied. The results revealed the developments of concentrated structural forces during the rising and falling process of the groundwater water level, indicating critical locations that should be strengthened. Meanwhile, both tunnels showed the same movement trend: settling first, floating afterwards and settling at last. And it is concluded that no reduction is required when calculating buoyancy in sands using measured pore pressure. Conclusions can provide a notable reference for future related research and engineering designs.