Hasil untuk "Ocean engineering"

Anusha Sathyanadh, Homa Esfandiari, Timothée Bourgeois et al.

Limiting global temperature rise below 2 °C requires significant reduction in greenhouse gas emissions and large-scale carbon dioxide removal (CDR). This study assesses the CO _2 sequestration and efficacy of two CDR approaches, bioenergy with carbon capture and storage (BECCS) and ocean alkalinity enhancement (OAE), applied individually and in combination. Using the Norwegian Earth System Model, simulations were designed to ramp up deployment of BECCS and OAE, to an additional area of 5.2 million km ^2 by 2100 for bioenergy feedstock for BECCS, and a CaO deployment rate of approximately 2.7 Gt yr ^−1 for OAE within the exclusive economic zones of Europe, the United States and China. The combined land–ocean CDR simulation revealed a largely additive carbon removal effect. Over 2030−2100, OAE sequestered 7 ppm of CO _2 with an accumulated 82.3 Gt CaO, achieving a CDR effectiveness of 0.08 ppm (∼0.17 PgC) per Gt CaO, while BECCS reduced 16 ppm of CO _2 , with CDR effectiveness of 3.1 ppm per million km ^2 of bioenergy crops. Together, the carbon removal achieved by BECCS and OAE corresponds to anthropogenic CO _2 emissions of 5.4 Gt CO _2 yr ^−1 by 2100, slightly more than 60% of current global transport sector emissions. Notably, the efficiency of BECCS and OAE alone was unaffected by their concurrent deployment. Nevertheless, simulations revealed distinct non-linear interactions, such as declines in land and soil carbon sinks in the combined scenario. Furthermore, all simulations show negligible effects on the global annual mean temperature. These results highlight near-additive CDR responses even under net-negative emissions, but feedback on land and ocean carbon sinks must be considered when designing CDR portfolios. This study provides new insights into CDR portfolio design and Earth system feedback under an overshoot scenario, highlighting both their potential and the need for continued emissions cuts and supportive policies.

Chengming Qin, Zhe Chen, Yanping He et al.

For deep-draft cylindrical platforms with a large annular column boot, the influence of the column boot diameter-to-height ratio (d/h) on motion performance remains unclear. This study investigates the effect of d/h on platform hydrodynamics while keeping the main body geometry, displacement, and draft unchanged. A hybrid numerical model validated against tests is adopted: STAR-CCM+ free-decay simulations identify equivalent linear damping, and ANSYS AQWA predicts hydrodynamic coefficients, response amplitude operators, and coupled time-domain responses under a 100-year survival sea state in the western South China Sea. Increasing d/h substantially increases heave added mass and added pitch moment of inertia, leading to longer natural periods and higher damping in heave and pitch. However, its effect on motion responses is non-monotonic and strongly response-dependent. As d/h increases, the responses are initially reduced markedly. The minimum surge and heave responses occur at d/h = 2.39 and 4.67, with reductions of about 34.0% and 87.2%, respectively, while the pitch response is already reduced by about 67.3% at d/h = 7.22. Further increases in d/h may weaken surge and heave mitigation while providing limited additional benefit for pitch. These findings provide qualitative understanding and quantitative guidance for response-oriented column boot design and optimization of similar platforms.

Hiroshi Kagemoto

Jonas Preine, Christian Hübscher, Dominik Pałgan et al.

Abstract Submarine explosive volcanism shapes seafloor morphology, impacts marine ecosystems, and poses risks to maritime infrastructure and coastal communities. However, its occurrences and drivers remain poorly constrained, especially for basaltic systems. Here we present evidence for widespread phreatomagmatic volcanism at the Reykjanes Ridge north of ~63.2°N, derived from high-resolution seismic reflection profiles, multibeam bathymetry, and seafloor imagery. Our data indicate a first-order depth control on eruption style: effusive volcanism dominates below ~300 m, producing hummocky edifices with strong seismic attenuation, whereas shallower depths favour Surtseyan eruptions, forming smooth volcanic cones with flanks comprising stratified, outward-dipping seismic reflections. When eruptions occur close to the water–air interface, flat-topped volcanoes form, some emerging as ephemeral islands before being submerged by storm wave base erosion. Our results show that Surtseyan eruptions have been a dominant and recurrent process along the Reykjanes Ridge north of ~63.2°N since the Last Glacial Maximum.

Lijuan Lu, Qinghua Yang, Marcus Gutjahr et al.

Abstract The Last Interglacial (128–113 ka B.P.) provides key insights into climate-carbon interactions under warm, high-CO2 conditions. While Antarctic temperature-driven Southern Ocean ventilation has been proposed to modulate atmospheric CO2, role of Southern Hemisphere westerlies (SHW) remains unclear. Here we synthesize 15 Antarctic and 5 subarctic Pacific export productivity records over two glacial-interglacial cycles. We find that Antarctic and subarctic productivity generally tracked Antarctic temperature and atmospheric CO2, but decoupled during Marine Isotope Stage 5, notably the Last Interglacial: high Antarctic productivity and CO2 persisted despite reduced subarctic productivity and over 6 °C Antarctica cooling. We suggest that poleward-intensified SHW strengthened upwelling of Circumpolar Deep Water, sustaining Antarctic productivity and atmospheric CO2, while altered Southern Ocean deep-water supply to the subarctic Pacific likely suppressed upwelling, limiting CO2 release. These findings identify SHW as key in polar ocean dynamics and carbon cycling, with implications for future climate under projected SHW intensification.

Divya Nair, Ashokan Laila Achu, Padinchare Veettil Gayathri et al.

The fast-growing aquaculture industry has increased worldwide use of antibiotics which lead to a global emergence of antimicrobial resistance, posing serious threats to aquatic life, humans, and the environment. This study aimed to investigate the patterns of antibiotic usage in both edible and ornamental fish farms in Kerala,India and the factors affecting these practices such as farming experience, training, education, disease prevalence, and expert recommendations for disease treatment. A cross-sectional spatial survey was conducted among 188 edible and ornamental fish farms across the state through structured questionnaires targeting antibiotic usage practices and associated risk factors. The result showed that farmers lack sufficient knowledge about aquatic pathogens, diagnostic methods, antimicrobial usage, dosages, and pharmacokinetics.Antibiotic use was 25.4 % higher in ornamental fish farms than in edible fish farms. Tetracycline was found to be the most common antibiotic used in both the edible (4.3 %) and ornamental (14.8 %) fish farms and was most prevalent in the Central (55 %) and Southern (30 %) regions of Kerala with lower usage in the Northern region (15 %) likely due to fewer farming operations and lower urbanization. Moreover, the main risk factors influencing antibiotic usage were frequent disease outbreaks, lack of access to trained professionals, reliance on peer advice, over-the-counter antibiotic availability, and absence of strict regulations. The study recommends the development of an effective strategy that will minimize the use of antibiotics and the risks they pose and to promote better farming practices that will improve fish health. These findings can support the development of policies that will regulate antibiotic usage and curb antimicrobial resistance in aquaculture systems.

Xu Xiang

Shavonna M. Bent, Shavonna M. Bent, Daniel Muratore et al.

Mesoscale eddies cause deviations from the background physical and biogeochemical states of the oligotrophic oceans, but how these perturbations manifest in microbial ecosystem functioning, such as community macromolecular composition or carbon export, remains poorly characterized. We present comparative lipidomes from communities entrained in two eddies of opposite polarities (cyclone–anticyclone) in the North Pacific Subtropical Gyre (NPSG). A previous work on this two-eddy system has shown differences in particulate inorganic carbon (PIC) and biogenic silica sinking fluxes between the two eddies despite comparable total organic carbon fluxes. We measured the striking differences between the lipidomes of suspended and sinking particles that indicate taxon-specific responses to mesoscale perturbations. Specifically, cyanobacteria did not appear to respond to increased concentrations of phosphorus in the subsurface of the cyclonic eddy, while eukaryotic microbes exhibit P-stress relief as reflected in their lipid signatures. Furthermore, we found that two classes of lipids drive differences between suspended and sinking material: sinking particles are comparatively enriched in phosphatidylcholine (PC, a membrane-associated lipid) and triacylglycerol (TAG, an energy storage lipid). We observed significantly greater export of TAGs from the cyclonic eddy as compared to the anticyclone and found that this flux is strongly correlated with the concentration of ballast minerals (PIC and biogenic silica). This increased export of TAGs from the cyclone, but not the anticyclone, suggests that cyclonic eddy perturbations may be a mechanism for the delivery of energy-rich organic material below the euphotic zone.

Weicheng Liu, Jichao Yang, Tongbo Xu et al.

This paper addresses the collaborative localization problem for unmanned surface vehicle (USV) clusters with random measurement delays. We propose a Cubature Kalman Hybrid Consensus Filter (CKHCF) based on the cubature Kalman filter (CKF) for widely distributed USV clusters lacking global communication capabilities. In this approach, each USV exchanges two pairs of information with all its neighbors and recalculates the received localization data based on distance and relative angle measurements. The recalculated information is then fused with the locally filtered data and updated to obtain localization information based on global measurements. To mitigate the impact of random measurement delays, we employ one-step prediction to compensate for delayed measurements. We present the derivation of the CKHCF algorithm and prove its consistency and boundedness using mathematical induction. Finally, we validate the effectiveness of the proposed algorithm through simulation experiments.

Zhixin Jin, Yongjiang Xu, Heting Zhou et al.

This study investigated the physiological responses to copper toxicity in liver and gill of juvenile yellowtail kingfish by exposing to 0 (control), 0.0672, 0.12, 0.214, 0.384, 0.672, 1.20, or 2.14 mg/L copper sulfate for 7 days and then recovered for 14 days. The histopathology, enzyme activities and differential gene expression were detected. The results indicate the safe concentration value of copper for juvenile yellowtail kingfish is 0.083 mg/L. Copper exposure caused structural damage to gill and liver, and could be disappeared or restored after the recovery period. Copper exposure enhanced the Cu,Zn superoxide dismutase (Cu/Zn-SOD) and glutathione peroxidase (GSH-Px) activities and the malondialdehyde (MDA) level in liver. However, with increasing copper concentrations, liver aspartate transaminase (AST) and gill Na+/K+-ATPase activities were at first enhanced and then inhibited. Serum lysozyme (LZM) and Cu/Zn-SOD activities were enhanced at low copper concentrations but inhibited at high concentrations, and the activities of alanine transaminase (ALT) and AST significantly increased at greater copper concentrations. After the recovery period, only liver Cu/Zn-SOD activity returned to control level. In contrast, liver GSH-Px activity and MDA levels and gill Na+/K+-ATPase activity, serum LZM and AST activities remained significantly higher than control, but liver AST activity, serum ALT, and Cu/Zn-SOD activities were significantly lower than control. We constructed the gene regulatory networks of molecular pathways in liver and gill in response to copper exposure. The DEGs were enriched mainly in the pathway of lipid metabolism in liver and pathway of oxidative phosphorylation in gill, indicating these respective pathways are involved in the response to copper stress in this species. The present results elucidate some histological, physiological, and molecular mechanisms underlying copper-exposure stresses in yellowtail kingfish, which could help guide the safe utilization of copper sulfate in disease control of farmed individuals.

Dun Li, Kanwal Ahmed, Zhiyun Zheng et al.

Numerous studies have been conducted to meet the growing need for analytic tools capable of processing increasing amounts of textual data available online, and sentiment analysis has emerged as a frontrunner in this field. Current studies are focused on the English language, while minority languages, such as Roman Urdu, are ignored because of their complex syntax and lexical varieties. In recent years, deep neural networks have become the standard in this field. The entire potential of DL models for text SA has not yet been fully explored, despite their early success. For sentiment analysis, CNN has surpassed in accuracy, although it still has some imperfections. To begin, CNNs need a significant amount of data to train. Second, it presumes that all words have the same impact on the polarity of a statement. To fill these voids, this study proposes a CNN with an attention mechanism and transfer learning to improve SA performance. Compared to state-of-the-art methods, our proposed model appears to have achieved greater classification accuracy in experiments.

Van Chien Pham, Hanseok Kim, Jae-Hyuk Choi et al.

Recent developments in power electronics, energy storage systems, and renewable energy; increased market demands for more efficient and cleaner electric power to meet stricter environmental regulations; and development in gigawatt (GW)-class DC (direct current) transmission systems for transmission of greater power over longer distances than similar alternative current (AC) systems, have supported the development of the DC grid, making it a promising solution for both the onshore and offshore industries. This paper presents an experimental study on the effectiveness of an engine speed reduction strategy on exhaust gas emission and fuel consumption when applied to a 4-stroke generator engine equipped with a cam-driven plunger diesel injection system. The experiments were performed on an 8-cylinder V-type 4-stroke generator engine installed in the MASTC laboratory, which is the only demonstration testbed for the ship’s electric propulsion system in Korea. Experimental results showed that fuel consumption decreased, but emission mass fraction in exhaust gas increased when maintaining engine power while reducing engine speed. This study has shown economic benefits in reducing fuel consumption, but incurred penalties for the emission performance of 4-stroke generator engines equipped with cam-driven plunger diesel injection systems when applying the engine speed reduction strategy.

Hongmin Zhou, Zhe Wang, Wu Ma et al.

Land surface albedo (LSA) is one of the driving factors in the energy balance of surface radiation and the interaction between the earth and atmosphere. LSA is an important parameter that is widely used in surface energy balance, medium- and long-term weather forecasting, and global change studies. GF-1 wide field view (WFV) data provide a spatial resolution of 16 m and temporally intensive land surface observations, but efficient algorithm was still lacking for quantitatively land surface parameters estimation. It is essential to improve the data use ability by generating efficient land surface parameter retrieval algorithms. This study proposed an LSA retrieval algorithm by using GF-1 WFV data. Land surface bidirectional reflectance distribution function characteristic parameters were used to represent the non-Lambertian characteristic of land surface. The top of atmosphere (TOA) reflectance is simulated by the 6S radiative transfer model by considering non-Lambertian land surfaces. Linear regression is applied in the TOA reflectance, and LSA is simulated with the surface bidirectional reflectance characteristic parameters to build a lookup table. The proposed algorithm can estimate LSA with high accuracy according to the TOA reflectance without the complex multistep inversion process. The validation results of ground measurements in Northwest China for different land cover types show that the algorithm is effective, and the overall root mean square error was 0.036 when compared with field observation. The algorithm also shows great consistency with Landsat albedo data. The proposed algorithm is of great significance for improving GF data utilization.

Jinbiao Lin, Ang Shi, Ziwu Zheng et al.

In this work, a simple and rapid method based on the lateral flow assay (LFA) has been developed for the detection of dual antibiotics. To achieve the quantitative assay and to reduce the non-specific adsorption, an internal system has been developed. A non-specific DNA was exploited as an internal standard and could be recognized by the DNA marker that was coated at the internal line. Two different kinds of aptamers were applied to recognize ampicillin (AMP) and kanamycin (KAM), and the distance between the detection line and conjugate pad was then optimized. Under the optimum conditions, the quantitative assays of AMP (R² = 0.984) and KAM (R² = 0.990) were achieved with dynamic ranges of 0.50 to 500.0 ng/L, and of 0.50 to 1000.0 ng/L, respectively. The LOQs of AMP and KAM were 0.06 ng/L and 0.015 ng/L, respectively. Finally, the proposed method has been successfully applied to analyze aquaculture water, tap water, and lake water, and hospital wastewater, indicating the established method could be used to monitor the environment.

Han Zhang, Lin Wang

Abstract Evapotranspiration is an important component of the water cycle, and possible trends in evapotranspiration can, among others, influence water management and agricultural production. Potential evapotranspiration (ETp) is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration. It plays an important role in assessing regional dry–wet conditions and variations in meteorological conditions. This study analyzed the change trends of monthly ETp and surface dryness and wetness in the Hancang River Basin and, through principal component analysis and correlation analysis, explored the main meteorological factors that affected ETp and the interactions between meteorological factors; ETp values were estimated using the FAO-56 Penman–Monteith method. The results showed that there was a large gap in ETp between different months in the Hancang River Basin, with a trend of first increasing and then decreasing within a year. The highest monthly evapotranspiration was 114.119 mm (July), and the lowest was 42.761 mm (January). The maximum relative humidity index was 0.822 (August), and the minimum was -0.979 (January). The average temperature, precipitation, average relative humidity, and solar radiation are positive factors that affect ETp, while average air pressure is a negative factor that affects ETp. This study provides a reference for the wet conditions of small watersheds and for countermeasures to address climate change.

XU Jing - ming, HU Jie - zhen, DENG Pei - chang, WU Jing - quan, WANG Gui

In order to accurately understand the corrosion laws of tower tube materials in acidic atmosphere environment, and provide a theoretical basis for the anticorrosion optimization of offshore wind turbine tower tube structure, the dry and wet acid salt spray test was used to simulate the coastal atmospheric environment to corrode Q345D alloy steel for 24, 48, 72, 96, 168,240, 360， 480 h to study the corrosion laws of the tower tube material Q345D steel in this environment. The sample Q345D after each corrosion period was analyzed by X - ray diffractometer analysis (XRD), scanning electron microscope (SEM) observation, corrosion weight loss rate, electrochemical measurement and other methods. Results showed that the corrosion kinetics curve of Q345D followed the law of power function. With the increase of corrosion time, the corrosion rate of Q345D steel presented a trend of increasing change. The corrosion rate was fast within 168 h, and then slowed down from 168 h to 240 h, and slowly increased again after 320 h. Under the environment of coastal atmosphere, the corrosion products of Q345D mainly included β - FeOOH, Fe2O3, γ - FeOOH, Fe3O4 and ɑ - FeOOH. During the corrosion process, the formation of a small amount of ɑ - FeOOH slowed down the corrosion rate of the substrate. The self corrosion potential of rusty Q345D steel showed a trend of gradual increase with the extension of corrosion time. Within 168 h, the self corrosion current density was increased and the corrosion rate was increased; from 168 h to 240 h the self corrosion current density was decreased, the rust layer protection became better gradually, and the corrosion rate was reduced in this stage; and from 240 h to 480 h the corrosion current density was increased and the corrosion rate was accelerated again.

N. Krishna kumar, R. Savitha, Abdullah Al Mamun

Yordan Garbatov

A. Alessandri, S. Donnarumma, M. Martelli et al.

Autonomous ships represent one of the new frontiers of technological innovation in marine engineering, which demand the development of innovative control systems to guarantee efficient and safe navigation of vessels. A convenient control system should be able to command the several actuators installed on board in different conditions—for instance, during oceanic navigation, harbor approach, narrow channels, and crowed areas. Such tasks are accomplished by different switching controllers for high and low speed motion, which have to be orchestrated to ensure an effective maneuvering. An approach to the design of hierarchies of controllers for maneuvering and navigation of ships equipped with a standard propulsion configuration in both blue and narrow water is proposed. Different levels of control, from global to local, are defined and integrated to steer the vessel in such a way to increase the maneuvering capability in various scenarios.

Xiaomin Hua, Gaige Zheng

The range of fundamental phenomena and applications achievable by metamaterials (MMs) can be significantly extended by dynamic control over the optical response. A mid-infrared tunable absorber which consists of lithography-free planar multilayered dielectric stacks and germanium antimony tellurium alloy (Ge₂Sb₂Te₅, GST) thin film was presented and studied. The absorption spectra under amorphous and crystalline phase conditions was evaluated by the transfer matrix method (TMM). It was shown that significant tuning of absorption can be achieved by switching the phase of thin layer of GST between amorphous and crystalline states. The near unity (>90%) absorption can be significant maintained by incidence angles up to 75 under crystalline state for both transverse electric (TE) and transverse magnetic (TM) polarizations. The proposed method enhances the functionality of MMs-based absorbers and has great potential for application to filters, emitters, and sensors.