External Seawater Research Articles

A Circulation Study Based on the 2022 Sino–Vietnamese Joint Survey Data from the Beibu Gulf

This study analyzed the horizontal and vertical distribution characteristics of temperature and salinity in the central and eastern regions of the Beibu Gulf, based on conductivity measurements in summer 2022, temperature, and depth (CTD) measurement data from the Sino–Vietnamese cooperative project “Demonstration Study on Ecological Protection and Management in Typical Bays: Seasonal Survey of the Beibu Gulf”. Furthermore, the study utilized the computational results from the numerical Finite-Volume Coastal Ocean Model (FVCOM) to elucidate the intrinsic patterns that formed the temperature and salinity distribution characteristics in August 2022 from both thermodynamic and dynamic perspectives. The circulation in the Beibu Gulf drives external seawater to move northward from the bay mouth. During this movement, numerous upwelling areas are created by lateral Ekman transport. The formation of different scales of cyclonic and anticyclonic vortices and current convergence zones is influenced by topography, runoff, and the water flux from the Qiongzhou Strait, which are key factors in the formation of upwelling and downwelling. The surface circulation in August 2022 significantly differed from the 20-year average surface circulation, with an influx of 1.15 × 104 m3/s more water entering the Beibu Gulf compared to the multi-year average. The water flux from the Qiongzhou Strait is a critical factor affecting the circulation patterns in the Beibu Gulf. The northeastern waters of the Beibu Gulf are characterized by current convergence zones, where extensive upwelling occurs. The rich nutrient salts in these areas promote the reproduction and growth of phytoplankton and zooplankton, making this the most favorable ecological environment in the Beibu Gulf and serving as a natural reserve for fisheries, coral reefs, dugongs, and Bryde’s whales.

The impact of acute low salinity stress on Antarctic echinoderms.

Climate change is causing increased coastal freshening in Antarctica, leading to reduced salinity. For Antarctica's endemic echinoderms, adapted to the stable polar environment, the impact of rapid reductions in coastal salinity on physiology and behaviour is currently unknown. Six common Antarctic echinoderms (the sea urchin Sterechinus neumayeri; the sea star Odontaster validus; the brittle star Ophionotus victoriae; and three sea cucumbers Cucumaria georgiana, Echinopsolus charcoti and Heterocucumis steineni), were directly transferred from ambient salinity (34.5‰) to a range of salinity dilutions (29-9‰) for 24 h. All species showed reduced activity and the establishment of a temporary osmotic gradient between coelomic fluid and external seawater. Most species exhibited a depression in oxygen consumption across tolerated salinities; however, at very low salinities that later resulted in mortality, oxygen consumption increased to levels comparable to those at ambient. Low salinity tolerance varied substantially between species, with O. victoriae being the least tolerant (24 h LC50 (lethal for 50% of animals) = 19.9‰) while E. charcoti and C. georgiana demonstrated the greatest tolerance (24 h LC50 = 11.5‰). These findings demonstrate the species-specific response of Antarctica's endemic echinoderms to short-term hypoosmotic salinity events, providing valuable insight into this phylum's ability to respond to an underreported impact of climate change.

Experimental and numerical study on the flow and heat transfer of ring-ribbed tank in deep-sea manned submersible

The ring-ribbed tank is the key equipment of cooling system of deep-sea manned submersible. The heat transfer characteristics of the outer wall and the heat transfer and flow characteristics of the inner flow channel of the ring-ribbed tank for different inlet and outlet temperatures and flow rates were studied through a water tank test. The results indicate that Nusselt number for the inner flow channel correlates with Reynolds and Prandtl numbers, while for the outer wall, it correlates with Grashof and Prandtl numbers with an overall error within 5%. A numerical study using the Realizable k-ε turbulence model and Boussinesq approximation of the flow-solid conjugate heat transfer is conducted, which can accurately determine the heat exchange capacity and the import and export differential pressure with an average relative error of 1.98% for hot water temperature and 7.73% for shell wall temperature. Additional simulations for determining the heat transfer capacity and flow resistance characteristics of the ring-ribbed tank in open water results demonstrate that the differential pressure and its coefficient are basically consistent with model test results. The cooling system can achieve a heat transfer rate of up to 17 kW with an external seawater flow velocity of approximately 2 knots.

Ages and geochemistry of garnet reveal multi-types of iron-copper mineralization in the Eastern Tianshan, NW China

The Aqishan-Yamansu Fe-Cu-Au metallogenic belt in the Eastern Tianshan, NW China, hosts numerous Fe and Fe-Cu deposits that may have different genetic models, such as volcanic-hosted and skarn/IOCG types. These variations in genetic models are attributed to whether the mineralization is associated with hydrothermal activity related to volcanic or intrusive rocks. This study primarily focuses on garnets formed during the early skarn alteration in the Shuanglong Fe-Cu and Shaquanzi Fe deposits within this belt. Garnets from the Shuanglong deposit can be divided into two types and exhibit general homogeneity, with SL-Grt1 being Fe-rich and subsequently replaced by the Fe-poor SL-Grt2. Garnets from the Shaquanzi deposit display complex zonation patterns, SQZ-Grt1 show core–oscillatory zoned rim and SQZ-Grt2 show core–mantle–oscillatory zoned rim. Laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) dating of SL-Grt1 and SL-Grt2 produced lower intercept 206Pb/238U ages ranging from 318.0 ± 6.4 Ma to 303.7 ± 16.4 Ma, coinciding with the multi-stage granite occurrence. In contrast, SQZ-Grt1 and SQZ-Grt2 yielded ages between 328.0 ± 2.6 Ma and 320.4 ± 1.7 Ma, corresponding to the timing of the hosted rhyolite. SL-Grt1 show light rare earth element (LREE) enrichment, and low concentrations of high field strength elements (HFSE), such as V and Zr, and appears to have formed rapidly within an open system. Conversely, SL-Grt2 is characterized by heavy rare earth element (HREE) enrichment and elevated HFSE contents, which could be formed slowly in a closed system. The variable composition in the SQZ-Grt1 and SQZ-Grt2 record cyclical changes in fluid kinetics (vigorous fluid flow vs. fluid stagnation). The cyclical zones in SQZ-Grt2 with HREE and HFSE concentrations below the detection limit indicate multiple inputs of external seawater. The distinct characteristics between Shuanglong and Shaquanzi garnets may reflect the difference between the single magma intrusion and complex volcanic activity. Combining previously published chronological data, this study elucidates a transition from the Middle Carboniferous volcanic-hosted Fe deposits (335–320 Ma) to the Late Carboniferous intrusion-related skarn or IOCG type Fe-Cu deposits (310–300 Ma) in the Aqishan-Yamansu belt.

Compression and Splitting Tensile Strength Model of Recycled Seawater and Sea Sand Concrete after Seawater Freeze–Thaw Cycles

Using seawater, sea sand, and recycled bricks to make concrete for nearshore and marine engineering can save resources and protect the environment. Therefore, this article studies the mechanical degradation law and failure mechanism of recycled seawater and sea sand concrete (SSC) after seawater freeze–thaw (SFT) cycles. Using the replacement rate of recycled brick coarse aggregate as a variable, the mass loss rate, relative dynamic elastic modulus, compression and splitting tensile strength, and microstructure changes of specimens under different SFT cycles were tested, and a mechanical performance degradation model was established. The results indicate that the SFT failure of recycled brick coarse aggregate SSC results from the action of physical SFT and chemical crystallization. Friedel’s salts without cementitious properties and ettringite with expansive properties are generated inside the concrete due to the chloride and sulfate ions in the internal concrete and external seawater reacting with cement hydration products. The formation of harmful crystals leads to the loosening of the concrete, especially in the interface area between brick aggregates and cement. The calculated results of the mechanical model established in this article agree with the test results. The compression and splitting tensile strength decrease linearly with the increase in SFT cycles.

Behavioural and physiological impacts of low salinity on the sea urchin Echinus esculentus.

Reduced seawater salinity as a result of freshwater input can exert a major influence on the ecophysiology of benthic marine invertebrates, such as echinoderms. While numerous experimental studies have explored the physiological and behavioural effects of short-term, acute exposure to low salinity in echinoids, surprisingly few have investigated the consequences of chronic exposure, or compared the two. In this study, the European sea urchin, Echinus esculentus, was exposed to low salinity over the short term (11‰, 16‰, 21‰, 26‰ and 31‰ for 24 h) and longer term (21, 26 and 31‰ for 25 days). Over the short term, oxygen consumption, activity coefficient and coelomic fluid osmolality were directly correlated with reduced salinity, with 100% survival at ≥21‰ and 0% at ≤16‰. Over the longer term at 21‰ (25 days), oxygen consumption was significantly higher, feeding was significantly reduced and activity coefficient values were significantly lower than at control salinity (31‰). At 26‰, all metrics were comparable to the control by the end of the experiment, suggesting acclimation. Furthermore, beneficial functional resistance (righting ability and metabolic capacity) to acute low salinity was observed at 26‰. Osmolality values were slightly hyperosmotic to the external seawater at all acclimation salinities, while coelomocyte composition and concentration were unaffected by chronic low salinity. Overall, E. esculentus demonstrate phenotypic plasticity that enables acclimation to reduced salinity around 26‰; however, 21‰ represents a lower acclimation threshold, potentially limiting its distribution in coastal areas prone to high freshwater input.

Modeled foraminiferal calcification and strontium partitioning in benthic foraminifera helps reconstruct calcifying fluid composition

Foraminifera are unicellular organisms that inhabit the oceans. They play an important role in the global carbon cycle and record valuable paleoclimate information through the uptake of trace elements such as strontium into their calcitic shells. Understanding how foraminifera control their internal fluid composition to make calcite is important for predicting their response to ocean acidification and for reliably interpreting the chemical and isotopic compositions of their shells. Here, we model foraminiferal calcification and strontium partitioning in the benthic foraminifera Cibicides wuellerstorfi and Cibicidoides mundulus based on insights from inorganic calcite experiments. The numerical model reconciles inter-ocean and taxonomic differences in benthic foraminifer strontium partitioning relationships and enables us to reconstruct the composition of the calcifying fluid. We find that strontium partitioning and mineral growth rates of foraminiferal calcite are not strongly affected by changes in external seawater pH (within 7.8–8.1) and dissolved inorganic carbon (DIC, within 2100–2300 μmol/kg) due to a regulated calcite saturation state at the site of shell formation.

The physiological consequences of a very large natural meal in a voracious marine fish, the staghorn sculpin (Leptocottus armatus).

Little information exists on physiological consequences when wild fish eat natural food. Staghorn sculpins at 10-13°C voluntarily consumed 15.8% of their body mass in anchovies. Gastric clearance was slow with >60% of the meal retained in the stomach at 48 h, and was not complete until 84 h. At 14-24 h post-feeding, pH was depressed by 3 units and Cl- concentration was elevated 2-fold in gastric chyme, reflecting HCl secretion, while in all sections of the intestine, pH declined by 1 pH unit but Cl- concentration remained unchanged. PCO2and total ammonia concentration were greatly elevated throughout the tract, whereas PNH3and HCO3- concentration were depressed. Intestinal HCO3- secretion rates, measured in gut sacs in vitro, were also lower in fed fish. Whole-animal O2 consumption rate was elevated approximately 2-fold for 72 h post-feeding, reflecting 'specific dynamic action', whereas ammonia and urea-N excretion rates were elevated about 5-fold. Arterial blood exhibited a modest 'alkaline tide' for about 48 h, but there was negligible excretion of metabolic base to the external seawater. PaCO2and PaO2remained unchanged. Plasma total amino acid concentration and total lipid concentration were elevated about 1.5-fold for at least 48 h, whereas small increases in plasma total ammonia concentration, PNH3and urea-N concentration were quickly attenuated. Plasma glucose concentration remained unchanged. We conclude that despite the very large meal, slow processing with high efficiency minimizes internal physiological disturbances. This differs greatly from the picture provided by previous studies on aquacultured species using synthetic diets and/or force-feeding. Questions remain about the role of the gastro-intestinal microbiome in nitrogen and acid-base metabolism.

The roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification

Two ocean acidification studies about egg hatching success (HS) in geographically important marine copepods, Calanus finmarchicus and C. helgolandicus, were reanalyzed with improved statistical procedures. The new results at low and moderate levels of seawater acidification showed no HS inhibition at normal habitat temperatures but statistically significant inhibition at warmer and colder temperatures. These HS results were compared with seawater carbonate system and borate concentrations from precise seawater measurements. The temperature dependent differences in HS could not be directly explained by changes in the seawater concentrations of either H+, bicarbonate (HCO3−), or CO2* (CO2* being the sum of unhydrated CO2 and H2CO3). In contrast, HS differences did match trends in seawater carbonate (CO32−) concentrations. A numerical model was developed which evaluates the concentrations of O2 or CO2*, HCO3−, and CO32− at the cellular level across an egg and embryo by considering both gas diffusion with the seawater and respiration by the embryo. Again, temperature-dependent trends in HS could not be explained changes in intracellular CO2* or HCO3− concentrations, but HS did trend with the changes in intracellular CO32− concentrations. Carbonate ions form strong coordination complexes with metals, so acidification-driven decreases in external seawater carbonate concentrations, which are amplified at warmer temperatures, could release injurious metals, thus driving the HS inhibition at warmer temperatures. Increases in cytoplasmic carbonate concentrations at warmer temperatures caused by seawater acidification could complex with biochemically-needed nutrient-type metals within the cells, also causing the increased HS inhibition at warmer temperatures. Furthermore, boron is essential in chemically signaling within and between cells. Seawater borate concentrations were closely correlated with HS inhibition via Michaelis-Menton equations, suggesting that acidification-driven decreases in seawater borate concentrations may also inhibit HS. Finally, the acidification-driven increases in CO2 diffusion into cells dramatically increased intracellular bicarbonate concentrations. At mild levels of seawater acidification, an organism might compensate by exporting bicarbonate from the cells to the haemolymph and then to the seawater. Although the energetic cost, as percentage of ATP production, might be high, increased respiration rates at warmer temperatures might better allow the organism to survive. However, as temperature is lowered, the cellular respiration rate declines more rapidly with respect to temperature than does the gas diffusion coefficient. Consequently, bicarbonate accumulation driven by inward CO2 diffusion might overwhelm the egg's bicarbonate export capacity at colder temperatures, explaining the colder temperature HS inhibition.

Design and experimental research of a novel deep-sea self-sustaining profiling float for observing the northeast off the Luzon Island

To understand the physical ocean laws of ocean circulation in the deep ocean below 2000 m, a profiling float named FUXING is presented to meet the deep-ocean observation requirements at a depth of 4000 m. First, to meet the low energy consumption and buoyancy regulation stability of the profiling float, the low–power buoyancy adjustment process of FUXING is effectively solved by introducing the external seawater pressure as the driving force. Then, to reduce the energy consumption of the single profile for the profiling float, the optimization of the oil draining adjustment mode in the floating process is studied. Simultaneously, a buoyancy-driven system characterization test was performed to examine the buoyancy adjustment of FUXING. When the frequency of oil draining is 15 times, the total energy consumption of FUXING is the lowest. Finally, FUXING was deployed in the northeast off the Luzon Island to validate the feasibility and reliability. The at-sea experiments indicated that the optimized oil draining adjustment mode can reduce the total energy consumption in the floating process by more than 20%. The profile data showed that the outer sea water gradually mixes with the South China Sea water after passing through the northeast off the Luzon Island.

How the green crab Carcinus maenas copes physiologically with a range of salinities.

To evaluate the physiological ability to adjust to environmental variations of salinity, Carcinus maenas were maintained in 10, 20, 32 (control), 40, and 50ppt (13.8 ± 0.6°C) for 7days. Closed respirometry systems were used to evaluate oxygen consumption ([Formula: see text]), ammonia excretion (Jamm), urea-N excretion (Jurea-N) and diffusive water fluxes (with 3H2O). Ions, osmolality, metabolites, and acid-base status were determined in the hemolymph and seawater, and transepithelial potential (TEP) was measured. At the lowest salinity, there were marked increases in [Formula: see text] and Jamm, greater reliance on N-containing fuels to support aerobic metabolism, and a state of internal metabolic alkalosis (increased [HCO3-]) despite lower seawater pH. At higher salinities, an activation of anaerobic metabolism and a state of metabolic acidosis (decreased [HCO3-] and increased [lactate]), in combination with respiratory compensation (decreased PCO2), were detected. TEP became more negative with decreasing salinity. Osmoregulation and osmoconformation occurred at low and high salinities, respectively, with complex patterns in individual ions; hemolymph [Mg2+] was particularly well regulated at levels well below the external seawater at all salinities. Diffusive water flux rates increased at higher salinities. Our results show that C. maenas exhibits wide plasticity of physiological responses when acclimated to different salinities and tolerates substantial disturbances of physiological parameters, illustrating that this species is well adapted to invade and survive in diverse habitats.

Durability of Fibre Reinforced Polymers in Exposure to Dual Environment of Seawater Sea Sand Concrete and Seawater.

The consequence of exposure to the dual environment of seawater sea sand concrete (SWSSC) on the inner surface and seawater (SW) on the outer surface on the durability of fibre reinforced plastic (FRP) confining tubes has received very limited research attention. The durability of FRPs fabricated with different fibre types was investigated for the application of SWSSC filled tubes and SWSSC-filled double-skin tubes exposed to the external environment of SW. The colour and shininess of carbon-fibre-reinforced polymer (CFRP) surfaces generally stayed unchanged even after 6 months of exposure to the dual environment, whereas basalt-fibre-reinforced polymer (BFRP) and glass-fibre-reinforced polymer (GFRP) tubes suffered degradation. The degradation led to a ~20–30% increase in pH; however, the pH increase in the external SW was more pronounced when the internal solution was SWSSC. The extent of degradation was greater in BFRP that in GFRP. The investigation also included a specialised investigation of the degradation at the fibre–matrix interface by fracturing specimens in liquid nitrogen.

Fuzzy Sliding Mode Control Method for AUV Buoyancy Regulation System

This paper investigates the control problem of the buoyancy regulation system for autonomous underwater vehicle (AUV). There are some problems to be considered in the oil-water conversion-based buoyancy regulation system, including the external seawater pressure, the pressure fluctuations, and the slow switching speed of the ball valve. The control accuracy of the buoyancy regulation under the traditional PID controller cannot meet the requirements of the project. In this paper, a fuzzy sliding mode control scheme is developed for the buoyancy regulation system to solve the abovementioned problems. At first, a mathematical model of the buoyancy regulation system is established, and the stability of the system is analyzed. Then, the sliding mode control algorithm is combined with the fuzzy system to improve the control accuracy. Finally, the pool-experiment results on a prototype show that the developed control scheme can meet the requirements of the control accuracy for the buoyancy regulation system.

The calcifying interface in a stony coral primary polyp: An interplay between seawater and an extracellular calcifying space

Stony coral exoskeletons build the foundation for the most biologically diverse marine ecosystems on Earth, coral reefs, which face major threats due to many anthropogenic–related stressors. Therefore, understanding coral biomineralization mechanisms is crucial for coral reef management in the coming decades and for using coral skeletons in geochemical studies. This study combines in–vivo imaging with cryo-electron microscopy and cryo–elemental mapping to gain novel insights into the biological microenvironment and the ion pathways that facilitate biomineralization in primary polyps of the stony coral Stylophora pistillata. We document increased tissue permeability in the primary polyp and a highly dispersed cell packing in the tissue directly responsible for producing the coral skeleton. This tissue arrangement may facilitate the intimate involvement of seawater at the mineralization site, also documented here. We further observe an extensive filopodial network containing carbon-rich vesicles extruding from some of the calicoblastic cells. Single-cell RNA-Sequencing data interrogation supports these morphological observations by showing higher expression of genes involved in filopodia and vesicle structure and function in the calicoblastic cells. These observations provide a new conceptual framework for resolving the ion pathway from the external seawater to the tissue-mineral interface in stony coral biomineralization processes.

Thermal Analysis of a Forced Flow Diffusion Absorption Refrigeration System for Fishing-Boat Exhaust Waste Heat Utilization

Ammonia water absorption refrigeration systems are effective in utilizing fishing-boat exhaust waste heat for cryopreservation. However, the liquid level control and the use of a solution pump characterized by small flowrate and high-pressure head result in poor reliability in the traditional system. Besides, the system must necessarily be designed anti-swaying and anti-corrosion. This paper proposes a forced flow diffusion absorption refrigeration system, in which an inherently leak-free canned motor pump and an ejector are employed to provide the driving forces of the gas and liquid loops. The approximate single pressure operation allows for a simple passive liquid sealing control without throttling valves. The system adopts an integrated cooling strategy which allows the system to operate under swaying conditions, and the external seawater cooled heat exchanger avoids internal corrosion and leakage. The thermal analysis shows the system is valid to be operated under wide operating conditions, and the coupled gas and solution circulation ratios determined the performance of the novel system. There is an optimal ammonia mass fraction difference in the gas loop to obtain the optimal COP. The COP reaches 0.4 when the temperatures at the outlets of the generator, evaporator, absorber, and condenser are 160, −15, 35, and 35°C, respectively. The novel system provides a reliable absorption refrigeration system design for fishing-boat applications.

In-situ element geochemical and sulfur isotope signature of pyrite and chalcopyrite: Constraints on ore-forming processes of the Laoshankou iron oxide-copper (-gold) deposit, northern East Junggar

The Laoshankou deposit is an iron oxide-copper–gold (IOCG)-like deposit in the northern margin of East Junggar, Central Asian Orogenic Belt (CAOB), in which pyrite is ubiquitous and present from stage II magnetite mineralization (Py1a and Py1b), stage III-A pyrite mineralization (Py2a and Py2b), to s tage III-B chalcopyrite mineralization (Py3a and Py3b). Despite of many previous studies, the source(s) of ore-forming fluids in the Laoshankou deposit are still controversial. Whether non-magmatic fluids were involved in the IOCG systems has also been highly debated in recent years. To further characterize the nature of ore-forming fluids in Paleozoic IOCG deposits in basin inversion settings, we conducted in-situ secondary ion mass spectrometry (SIMS) sulfur isotope and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace element analysis in a set of pyrite/chalcopyrite-bearing samples in the Laoshankou deposit. Sulfur isotope results of the sulfides in all stages (−3.5 to 2.6‰) fit in the magmatic sulfur range, indicating the contribution of magmatic sulfur. However, the weakly negative δ34S values of − 3.5‰ to − 1.5‰ (Py3), possibly indicating the addition of organic sulfur, which can also be proved by organic-rich fluid inclusions and strata. The low Se/S (<5 × 10−5), the volcanogenic-like Co/Ni ratios (3.9–28, average 16), and the varying Ni contents (81–978 ppm, average 315 ppm) of Py1 indicate that its magmatic sulfur was leached from mafic volcanic rocks by heated seawater in a reducing condition at stage II. The elevated Ni (433–3736 ppm, average 1401 ppm) and Se (39–143 ppm, average 80 ppm) contents, and the Se/S (∼1.5 × 10−4) ratios of Py2 indicate a more oxidizing condition. We suggest that the magmatic sulfur of Py2 in stage III-A was also leached from mafic rocks by seawater, but magmatic hydrothermal fluid input cannot be excluded. The high Co/Ni (7.7–415, average 142) and low Ni/Se (0.43–3.4, average 1.7) ratios, and the low Ni contents (31–381 ppm, average 133 ppm) of Py3 show that such organic sulfur was likely leached from organic-rich sequence by relatively low-temperature and reduced fluid, with significant contribution from the felsic rocks in stage III-B. Combined with previous halogen and C–H-O isotopes results, external non-magmatic fluids can be proved in the Laoshankou deposit. Stage III-B chalcopyrite grains replaced early-stage pyrites, during which some alleged less-mobile elements (e.g., Co, and As) in the replaced pyrites were released into the Cu ore-forming fluids and formed extremely low-Co, porous/fractured, and inclusion-rich Py1b and Py2b, together with high Co-As contents in the Py3 and the Py3-chalcopyrite boundary. We propose that external seawater and organic bittern brine may have an effect on the mineralization at Laoshankou. Combined with previous researches in the Andean and East Tianshan, external fluids may play a key role for the IOCG deposits in arc-related basin inversion setting.

Thermal insulation design of subsea vertical X-mas tree

Temperature drop is commonly observed in subsea vertical X-mas trees during shutdown. The presence of a huge temperature difference between internal crude oil and external seawater can cause severe equipment degradation of the oil flow channel (e.g., hydrate precipitation), which can block the oil flow channel and interrupt the production process. The most vulnerable parts of a subsea vertical X-mas tree tend to be components with high convective heat transfer rates, such as production modules and short joints. We proposed an innovative approach for the insulation design of underwater equipment under a shutdown condition. First, we obtained a heat transfer analysis of the tree under working conditions through computational fluid dynamics to ascertain the initial temperature condition for an unsteady-state analysis. Second, we investigated the unsteady heat transfer characteristics of the tree with an insulation layer in the shutdown state and derived the relationships between insulation duration and thickness by data analysis. We used data analysis to identify the relationship between insulation duration and thickness. Finally, we derived the empirical formula of insulation thickness for underwater equipment given the effect of environmental factors on the heat preservation effect. We performed the experiment with an oil pipeline, and the results showed that the internal oil of the equipment did not hydrate within 8 h under the shutdown condition with insulation layers.

Experimental Study on Internal and External Salt Attack from Seawater and Sea-Sand to Mortars

Seawater and sea-sand are potential material for concrete in marine environment. This paper aimed to study the influence of internal and external salt attack from seawater and sea-sand on the performance of mortars. Six groups of mortars with different salt attack types were designed. The length, mass, dynamic elastic modulus and pH value of all mortars were measured in the test. The hydrate phase was obtained by thermodynamic simulation, and the phase after 322 days attacked was detected by X-ray diffraction (XRD). Internal seawater and sea-sand attack could improve the early length change of mortars before 28 days. And the early mass growth rate of mortars of seawater mixed mortars was slow. While the influence of seawater and sea-sand on the early dynamic elasticity modulus was limited. The external environment was the main factor affecting the length, mass and dynamic elasticity modulus of mortars after 28 days. Differences of hydrate phases in different mortars were ettringite (AFT), monosulfate, hemicarbonate, monocarbonate, Friedel’s salt and Kuzel’s salt. The more salt in mixing materials, the larger the volume of hydration solid phase. The salt attack from seawater and sea-sand could increase pH of the simulated solution in mortars. Ettringite and brucite could be clearly observed by XRD in mortars attacked by external seawater, and gypsum and Friedel’s salt could be observed in all mortars. It was more reasonable to use mass to evaluate the deterioration degree of the mortars attacked by seawater or sea-sand.

Mapping coral calcification strategies from in situ boron isotope and trace element measurements of the tropical coral Siderastrea siderea

Boron isotopic and elemental analysis of coral aragonite can give important insights into the calcification strategies employed in coral skeletal construction. Traditional methods of analysis have limited spatial (and thus temporal) resolution, hindering attempts to unravel skeletal heterogeneity. Laser ablation mass spectrometry allows a much more refined view, and here we employ these techniques to explore boron isotope and co-varying elemental ratios in the tropical coral Siderastrea siderea. We generate two-dimensional maps of the carbonate parameters within the calcification medium that deposited the skeleton, which reveal large heterogeneities in carbonate chemistry across the macro-structure of a coral polyp. These differences have the potential to bias proxy interpretations, and indicate that different processes facilitated precipitation of different parts of the coral skeleton: the low-density columella being precipitated from a fluid with a carbonate composition closer to seawater, compared to the high-density inter-polyp walls where aragonite saturation was ~ 5 times that of external seawater. Therefore, the skeleton does not precipitate from a spatially homogeneous fluid and its different parts may thus have varying sensitivity to environmental stress. This offers new insights into the mechanisms behind the response of the S. siderea skeletal phenotype to ocean acidification.

Numerical Investigation of the Damage Mechanism of Offshore Pipeline Impacted by the Lump-Shaped Falling Object

AbstractDamage mechanism analysis of the exposed offshore pipeline impacted by lump-shaped falling objects plays a significant role in offshore pipeline design, inspection, maintenance, and protection. A series of three-dimensional (3D) coupling models are established and simulated to investigate mechanical behaviors and responses of exposed offshore pipelines impacted by lump-shaped falling objects. The effects of both offshore pipeline parameters and lump-shaped falling object parameters were discussed under the joint action of internal pressure and external seawater pressure. The results demonstrate that seabed soil could absorb partial impact energy and act as a cushion. Indentation on the pipeline top and stress concentrations on the pipeline bottom starts to appear when the impact velocity is larger than 10 m/s and 14 m/s, respectively. The critical impact energy before pipeline failure is around 9733.339 J. A variation in contact area has a noticeable influence on the dent depth, but a slight influence on the global deformation. An increase in pressure difference mitigates the impact damage. The depression rate increases with the rise of the radius-thickness ratio, and the most severe plastic deformation occurs when the radius-thickness ratio is 40. Besides, the eccentric distance is an essential factor influencing the damage mechanism of the offshore pipeline.