Hasil untuk "Ocean engineering"

Mehmet Melikoglu

Yiwei Xu, Jie Wang, Libin Zhu et al.

A shipborne campaign was conducted in China’s southeastern coastal waters (21° N–32° N) from 14 to 31 January 2024 to investigate atmospheric CO₂ and CH₄ concentrations and their offshore gradients. Advanced instrumentation enabled high-precision measurements, validated by canister sampling with strong correlations to reference data. The voyage employed a dual-route design: a northbound baseline along the mainland coast and a southbound route with offshore excursions up to 80 nm, facilitating the first quantification of GHG gradients in the continental shelf region. Baseline concentrations from the northbound route revealed regional variability: CO₂ levels ranged from 422.75 ± 9.96 ppm (Fujian) to 445.62 ± 1.51 ppm (Zhejiang), while CH₄ levels spanned 2005.78 ± 5.89 ppb (Fujian) to 2064.59 ± 13.93 ppb (Zhejiang). Southbound analysis at 10 nm intervals showed CO₂ gradients transitioning from positive to negative at ~30 nm and back to positive at ~70 nm, whereas CH₄ exhibited complex behavior, including a positive–negative–positive transition at 30–40 nm and consistent increase beyond 50 nm. Under winter monsoon conditions, transport flux analysis identified eastward CO₂ fluxes of 3819.55–6587.77 g·m⁻²·s⁻¹ and CH₄ fluxes of 6.42–11.42 g·m⁻²·s⁻¹. Southward transport diminished along the coast, with CO₂ fluxes declining from 5741.07 to 879.76 g·m⁻²·s⁻¹ and CH₄ fluxes from 9.84 to 1.49 g·m⁻²·s⁻¹ between Zhoushan and Hong Kong. The Taiwan Strait demonstrated a funneling effect, enhancing southward transport. These findings address data gaps in ocean regions and provide insights for future GHG monitoring.

Shan Gao, Haolei Song, Tong Zang et al.

The present study investigates the impact of femtosecond laser shock peening (FLSP) on the corrosion resistance of an AZ31 magnesium alloy. The alloy was subjected to irradiation with varying pulse energies in an air environment, and subsequent modifications in surface properties were characterized. Surface wettability, assessed by contact angle measurements, indicated enhanced hydrophobicity following FLSP, especially at higher pulse energies. Corrosion behavior after immersion with various durations was assessed in a 3.5% NaCl solution using electrochemical polarization curves and electrochemical impedance spectroscopy, applying a three-electrode system. The results revealed that FLSP significantly augmented corrosion resistance; the most notable effects were observed at higher pulse energies. SEM/EDS analysis post-corrosion revealed a transition from localized to more uniform corrosion, accompanied by reduced pit size and density. XRD and XPS confirmed the formation of a protective Mg(OH)₂ layer, which exhibited greater stability and uniformity at higher laser energies. The study concluded that FLSP represented an effective approach for enhancing the corrosion resistance of the AZ31 magnesium alloy, with potential applications in improving the longevity of magnesium alloy components in industrial settings.

Shiwu Zhang, Shengkai Zhao, Zhen Sun et al.

This study investigates the air movement preference of males and females after moderate-intensity exercise. 35 participants dressed in 0.6 clo exercised for 15 min in a room at 30 °C and then entered another room at 24 °C/26 °C/28 °C. During the experiment, participants were able to adjust the fan speed according to their own thermal comfort needs. The results indicate that after a change in metabolic rate, female prefer higher fan usage and greater air movement compared to males. When the body returns to thermal comfort, male have higher fan usage and prefer higher air movement than female. There were no difference in subjective evaluation and skin temperature between female and male. However, the skin evaporative heat loss of female was significantly lower than that of male. The correlation between air temperature, air speed and the time after entering the room tailored to the thermal requirements of distinct genders following moderate-intensity exercise has been established, which can provide a comprehensive control strategy for achieving both comfortable and energy-efficient thermal environments.

Deming Chen, Mingchen Lin, Jinxin Zhou et al.

The integrated development of offshore wind power and marine aquaculture represents a promising approach to the sustainable utilization of ocean resources. The present study investigated the hydrodynamic response of an innovative combination of a wind farm monopile and pontoon raft aquaculture facilities (PRAFs). Physical water tank experiments were conducted on PRAFs deployed around a wind farm monopile using the following configurations: single- and three-row arrangements of PRAFs with and without a monopile. The interaction between the aquaculture structure and the wind farm monopile was examined, with a particular focus on the mooring line tensions and bridle line tensions under different wave conditions. Utilizing the wind farm monopile foundation as an anchor, the mooring line tension was reduced significantly by 16–66% in the single-row PRAF. The multi-row PRAF arrangement experienced lower mooring line tension in comparison with the single-row PRAF arrangement, with the highest reduction of 73%. However, for the bridle line tension, the upstream component was enhanced, while the downstream one was weakened with a monopile, and they both decreased in the multi-row arrangement. Finally, we developed numerical models based on flume tank tests that examined the interactions between the monopile and PRAFs, including configurations of a single monopile, along with single- and three-row arrangements of PRAFs. The numerical simulation results confirmed that the monopile had a dampening effect on the wave propagation of 5% to 20%, and the impact of the pontoons on the monopile was negligible, implying that the integration of aquaculture facilities around wind farm infrastructure may not significantly alter the hydrodynamic loads experienced by the monopile.

Jie Zhang, Hui Liu, Yusheng He et al.

Maritime communication plays a crucial role in fields such as ocean resource exploration and marine environmental monitoring. Existing maritime communication methods either face challenges in equipment deployment or are limited by high power requirements, making sustained operation difficult. The emergence of LoRa presents an opportunity in this regard, with its characteristics of low power consumption and long communication range, meeting the demands for long-term maritime communication. However, LoRa’s underlying implementation is not open-source, and LoRaWAN itself adopts a star topology, limiting communication between nodes. Therefore, we have devised a communication packet header working at the application layer to enable peer-to-peer communication between nodes. Our on-campus field tests have shown that our system can achieve node-to-node communication, networking functionalities, with a packet delivery rate more than 94%, and max data transmission rate can achieve 1027 bps. In the sea test, the communication rate of our node remained basically around 1035 bps due to the absence of objects blocking the line of sight, and packet delivery rate was more than 96%. The byte error rates of all experiments were less than 0.5%.

Ludovica Sartini, Alessandro Antonini

LI Yifan 1, 2, LI Dayong 3, ZHANG Yukun 2

The steel piles and steel suction caissons are widely used in ocean engineering, in which the mechanical behaviors of the interface between soils and foundations determine their bearing capacities. A series of saturated sand–steel interface drained shear tests are conducted to reveal the effects of the grain size distribution, surface texture and normal confinement conditions on interfacial shear behaviors. The research shows that due to the differences in the shear mode of sand particles and the dissipation of the pore water pressure, the shear stress-displacement curve under a constant normal load (CNL) experiences an obvious strain-softening phenomenon, whereas the maximum shear stress increases with the increase of the normal stress increment under a variable normal load (VNL). For the smooth and convex surfaces, the interfacial friction angle increases linearly with the increase of Cu. For the groove surfaces, the interfacial friction angle decreases with the increase of Cu. The shear efficiency of the saturated sand-steel plate interface is greatly influenced by water, and the presence of the water film weakens the friction between sand particles and steel plates, thus, the maximum efficiency cannot be developed on interfaces.

Xi Liu, Mouyan Jiang, Mouyan Jiang et al.

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that play important roles in several biological processes, including the regulation of body color. Leopard coral grouper (Plectropomus leopardus) is a valuable marine aquaculture fish; however, at present, there are no published reports on its early body color development. The skin color of P. leopardus undergoes a transition from transparent to red from 26 days post-hatching (dph) to 30 dph. In this study, we performed miRNA sequencing on 26 dph (Transparent, PT) and 30 dph (Red, PR) skin samples of P. leopardus to explore the molecular mechanism underlying red color formation. A total of 44.31 M and 37.55 M clean tags were obtained from PT and PR group, respectively. Among these tags, 981 miRNAs were identified, including 493 known and 488 novel miRNAs. A total of 106 differentially expressed miRNAs (DEMs) were identified in PT vs. PR, with 43 up-regulated and 63 down-regulated miRNAs in the PR group, compared to the PT group (|fold change| > 2 and p-value < 0.05). A miRNA-mRNA network based on 18 candidate miRNAs and 53 target genes related to pigmentation, and KEGG enrichment analysis of the target genes of all DEMs, revealed that miRNAs involved in the formation of red skin color were mainly related to: 1) the inhibition of melanin synthesis (miR-141-z, miR-206-z, miR-206-y, miR-27-z, miR-137-y, miR-204-x, miR-204-y, miR-211-x, miR-211-z); 2) chromatophore development (miR-206-z, miR-206-y, miR-499-y, miR-1-z, miR-2188-x, miR-423-x); and 3) carotenoid metabolism (miR-204-x, miR-204-y, miR-499-y). This study demonstrates the potential role of miRNAs in red color formation and lays the foundation for the molecular mechanism of body color polymorphism in P. leopardus.

Haili Ma, Haili Ma, Xiaotong Xiao et al.

Continental marginal seas are key systems in the global carbon cycle. Carbon stocks represent the ability to store carbon, thus quantifying the carbon stocks in marine sediments would help to better understand their importance in the carbon cycle. In this study, 17 sediment cores in the mud areas of the South Yellow Sea and the East China Sea were measured for total organic carbon (TOC) and its stable isotope (δ13C), and dry bulk density; and from which the carbon stocks and carbon stock accumulation rate as well as marine/terrestrial carbon stocks/carbon stock accumulation rate were calculated. The carbon stocks in the mud area of the South Yellow Sea showed a decreasing trend during 1855 to 1950 caused by the relocation of the Yellow River Estuary in 1855, but increased after 1950s due to increased sediment input via the enhancement of South Shandong Coastal Current. In the Min-Zhe belt of the East China Sea, carbon stocks showed an overall high marine proportion due to the phytoplankton bloom induced by high nutrient level, but the decreased carbon stocks in recent decades were mainly caused by the construction of reservoirs in the Yangtze River that reduced sediment transports. The average carbon stocks in 1 m sediments from the South Yellow Sea (45.2 t ha-1) and Min-Zhe belt (52.8 t ha-1) were low compared to that of global marine sediments (66.6 t ha-1), while the carbon stock accumulation rate showed much higher values (0.1 t ha-1 yr-1 in South Yellow Sea and 0.31 t ha-1 yr-1 in the Min-Zhe belt) because of higher sedimentation rates. Although carbon stocks of Chinese marginal seas were also lower than that of the tidal flats (70.7 t ha-1) and wetland (123.6 t ha-1) in China, their much larger area could store 0.75 Pg C in marine sediments. Our temporal records suggest that anthropogenic activities have reduced carbon stocks in the marginal seas since 1950, causing carbon to re-enter the atmosphere to impact climate changes.

Kristina D. A. Mojica, Corina P. D. Brussaard

The field of aquatic viral ecology has continued to evolve rapidly over the last three decades [...]

Romain Hascoët

Seon-Jae Jeon, Dong-Wook Seo

Wireless power transfer (WPT) technology has been widely introduced and developed over the past few years. Nevertheless, the basic WPT configuration using one transmitting (Tx) coil and one receiving (Rx) coil still achieves very limited performance in terms of power transfer distance. To overcome this limitation, various multi-coil WPT systems using three or more coils have been studied. Among them, a multiple-input single-output (MISO) structure can provide the Rx with advanced freedom in an extensive lateral area. However, few studies have investigated how far multi-Tx coils can increase the transfer distance. In this paper, we analyze the transfer distance and lateral coverage based on the generalized critical coupling condition and system energy efficiency according to the number of additional Tx coils in the MISO WPT system. The results demonstrate that the MISO WPT system using planarly arranged Tx coils improves by barely 1% in the optimal transfer distance, which achieves the maximum output power condition in a single-Tx WPT system. To validate our analysis, the MISO WPT system with seven Tx coils and seven LCC inverters was implemented and its performance was assessed. The measured results agreed well with the theoretically calculated results.

Boce Chu, Jinyong Chen, Jie Chen et al.

Due to the different imaging mechanisms between optical and polarimetric synthetic aperture radar (PolSAR) images, determining how to effectively use such complementary information has become an interesting and challenging problem. Convolutional neural networks (CNNs) and other deep neural networks have achieved good experimental results in remote sensing land-cover semantic segmentation. However, the CNN convolution structure can extract only the features within the receptive field in the spatial dimension without focusing on the relationship between multiple channels; therefore, it is impossible to realize fusion and complementarity between multiple channels. In this article, we propose a novel spatial dense channel attention fusion network (SDCAFNet), which takes optical and PolSAR images as different inputs and completes feature fusion and semantic segmentation within a neural network. First, SDCAFNet uses a two-stream siamese CNN network to realize the preliminary feature coding of optical and PolSAR images. Then, a spatial dense channel attention module (SDCAM) is proposed. The channel activation values obtained at different positions are combined in the spatial dense matrix, which can describe the attention in the feature fusion process. Finally, we introduce the fused features into the symmetric skip-connection decoder composed of multiple symmetric decoder blocks to realize end-to-end land-cover semantic segmentation. Experimental results show that SDCAFNet can effectively learn the correlation between optical and PolSAR channels and has a better segmentation accuracy than other methods.

Jia-Jie Han, Ya Li, Hsiang-nan Li et al.

Abstract We reanalyze the $$\Lambda _b\rightarrow p$$ Λ b → p transition form factors in the perturbative QCD (PQCD) approach by including higher-twist light-cone distribution amplitudes (LCDAs) of a $$\Lambda _b$$ Λ b baryon and a proton. The previous PQCD evaluation performed decades ago with only the leading-twist $$\Lambda _b$$ Λ b baryon and proton LCDAs gave the form factors, which are two orders of magnitude smaller than indicated by experimental data. We find that the twist-4 $$\Lambda _b$$ Λ b baryon LCDAs and the twist-4 and -5 proton LCDAs contribute dominantly, and the enhanced form factors become consistent with those from lattice QCD and other nonperturbative methods. The estimated branching ratios of the semileptonic decays $$\Lambda _b\rightarrow p\ell {\bar{\nu }}_\ell $$ Λ b → p ℓ ν ¯ ℓ and the hadronic decay $$\Lambda _b\rightarrow p\pi $$ Λ b → p π are also close to the data. It implies that the b quark mass is not really heavy enough, and higher-power contributions play a crucial role, similar to the observation made in analyses of B meson transition form factors. With the formalism established in this work, we are ready to study various exclusive heavy baryon decays systematically in the PQCD approach.

Janusz T. Cieśliński, Slawomir Smolen, Dorota Sawicka

The results of experimental investigation of free convection heat transfer in a rectangular container are presented. The ability of the commonly accepted correlation equations to reproduce present experimental data was tested as well. It was assumed that the examined geometry fulfils the requirement of no-interaction between heated cylinder and bounded surfaces. In order to check this assumption recently published correlation equations that jointly describe the dependence of the average Nusselt number on Rayleigh number and confinement ratios were examined. As a heat source served electrically heated horizontal tube immersed in an ambient fluid. Experiments were performed with pure ethylene glycol (EG), distilled water (W), and a mixture of EG and water at 50%/50% by volume. A set of empirical correlation equations for the prediction of Nu numbers for Rayleigh number range 3.6 × 10⁴ < Ra < 9.2 × 10⁵ or 3.6 × 10⁵ < Ra_q < 14.8 × 10⁶ and Pr number range 4.5 ≤ Pr ≤ 160 has been developed. The proposed correlation equations are based on two characteristic lengths, i.e., cylinder diameter and boundary layer length.

Xingwen Quan, Yanxi Li, Binbin He et al.

Foliage fuel load (FFL) is a critical factor affecting crown fire intensity and rate of spread. Satellite observations provide the potential for monitoring FFL dynamics across large areas. Previous studies commonly used empirical methods to estimate FFL, which potentially lacks reproducibility. This study applied Landsat 7 ETM&#x002B; and 8 OLI data for FFL retrieval using radiative transfer model (RTM) and machine learning method. To this end, the GeoSail, SAIL, and PROSPECT RTMs were first coupled together to model the near-realistic scenario of a two-layered forest structure. Second, available ecological information was applied to constrain the coupled RTM modeling phases in order to decrease the probability of generating unrealistic simulations. Third, the coupled RTMs were linked to three machine learning models&#x2014;random forest, support vector machine, and multilayer perceptron&#x2014;as well as the traditional lookup table. Finally, the performance of each method was validated by FFL measurements from Southwest China and Sweden. The resulting multilayer perceptron (<italic>R</italic>² &#x003D; 0.77, RMSE &#x003D; 0.13, and rRMSE &#x003D; 0.43) outperformed the other three methods. The evaluation of the applicability of the FFL estimates was conducted in a southwest China forest where two occurred in 2014 and 2020. The FFL dynamics from 2013 through 2020 showed that the fire was likely to occur when the FFL accumulated to a critical point (around 27 &#x00D7; 10⁶ kg), highlighting the relevance of remote sensing derived FFL estimates for understanding potential fire occurrence.

Jacob Arndt, Dalton Lunga

Remote sensing in combination with deep learning has become instrumental for efficiently and accurately classifying land-use and land-cover across large geographic areas. These technologies have also been successful in characterizing urban environments in terms of their structural units, structure types, or morphological regions. In these approaches, an urban area is partitioned into regions that exhibit homogeneous physical characteristics. However, existing approaches are typically limited to a single city, use inconsistent typologies, and lack scalability and generalization capacity. In this article, we propose an urban structural units categorization scheme and demonstrate its utility by applying it to 13 cities. Inspired by the lack of scalability and generalization capacity in urban structural units mapping, we extend the reach of deep learning and conduct a set of classification experiments in all 13 cities. These experiments offer insights into the strengths and limitations of deep neural networks for classifying urban structural units over diverse geographic regions and on heterogeneous collections of satellite imagery. The efficacy of the proposed deep learning approach is compared to a baseline method of multiscale image features and support vector machines. Our validation on five cities shows that better performance is achieved with deep neural networks. Additionally, we evaluate the impact of input size, model depth, and spatial pyramid pooling to assess the generalization capacity of deep neural networks.

Qiang Wang, Boran Zhang, Pengyao Yu et al.

The bow-flared section may be simplified in the prediction of slamming loads and whipping responses of ships. However, the difference of hydrodynamic characteristics between the water entry of the simplified sections and that of the original section has not been well documented. In this study, the water entry of several different bow-flared sections was numerically investigated using the computational fluid dynamics method based on Reynolds-averaged Navier–Stokes equations. The motion of the grid around the section was realized using the overset mesh method. Reasonable grid size and time step were determined through convergence studies. The application of the numerical method in the water entry of bow-flared sections was validated by comparing the present predictions with previous numerical and experimental results. Through a comparative study on the water entry of one original section and three simplified sections, the influences of simplification of the bow-flared section on hydrodynamic characteristics, free surface evolution, pressure field, and impact force were investigated and are discussed here.

M. Ismail, M.S. Yahya, N.A. Sazelee et al.

The catalytic effect of K2SiF6 on MgH2 was first timely studied. The MgH2 + 5 wt.% K2SiF6 was prepared via the ball milling technique. The catalyst had lessened the initial decomposition temperature by 134 °C and 48 °C as compared to both pristine and milled MgH2 samples, respectively. In 2 minutes, 4.5 wt.% of hydrogen was absorbed (250 °C) by the doped composite, which was 0.8 wt.% higher than the milled MgH2. Meanwhile, for the desorption kinetics (320 °C, 1 atm), the amount of desorbed hydrogen was increased by 2.4 wt.% and 2.3 wt.% for the first 10 and 20 minutes. Besides, contracting volume and Johnson-Mehl-Avrami models were used to analyse the kinetics sorptions. The decomposition activation energy calculated based on Kissinger equation was 114 kJ/mol. As for the active species, Mg2Si, MgF2 and KH were formed during the heating process. These active species are speculated to be responsible for the improvement of the hydrogenation properties of the composite.