Hasil untuk "Ocean engineering"

Ming Tong, Shenghua Fan, Jiu Jiang et al.

Recently, detectors based on deep learning have boosted the state-of-the-art of application on ship detection in synthetic aperture radar (SAR) images. However, constructing discriminative feature from scattering of background and distinguishing contour of ship precisely still present challenging subject to the inherent scattering mechanism of SAR. In this article, a dual-branch detection framework with perception of scattering characteristic and geometric contour is introduced to deal with the problem. First, a scattering characteristic perception branch is proposed to fit the scattering distribution of SAR ship through conditional diffusion model, which introduces learnable scattering feature. Second, a convex contour perception branch is designed as two-stage coarse-to-fine pipeline to delimit the irregular boundary of ship by learning scattering key points. Finally, a cross-token integration module following Bayesian framework is introduced to couple features of scattering and texture adaptively to learn construction of discriminative feature. Furthermore, comprehensive experiments on three authoritative SAR datasets for oriented ship detection demonstrate the effectiveness of proposed method.

Zeev Yampolsky, Itzik Klein

Autonomous underwater vehicles (AUVs) are underwater robotic platforms used in a variety of applications. An AUV’s navigation solution relies heavily on the fusion of inertial sensors and Doppler velocity logs (DVL), where the latter delivers accurate velocity updates. To ensure accurate navigation, a DVL calibration is undertaken before the mission begins to estimate its error terms. During calibration, the AUV follows a complex trajectory and employs nonlinear estimation filters to estimate error terms. In this paper, we introduce DCNet, a data-driven framework that utilizes a two-dimensional convolution kernel in an innovative way. Using DCNet and our proposed DVL error model, we offer a rapid calibration procedure. This can be applied to a trajectory with a nearly constant velocity. To train and test our proposed approach a dataset of 276 min long with real DVL recorded measurements was used. We demonstrated an average improvement of 70% in accuracy and 80% improvement in calibration time, compared to the baseline approach, with a low-performance DVL. As a result of those improvements, an AUV employing a low-cost DVL, can achieve higher accuracy, shorter calibration time, and apply a simple nearly constant velocity calibration trajectory. Our results also open up new applications for marine robotics utilizing low-cost, high-accurate DVLs.

Massimo Falchi, Patrick Cronin, Clement Courade et al.

The results of demonstration tests of a full-scale hydrokinetic turbine for river and tidal sites, are presented at the conclusion of the EU-funded CRIMSON project. The turbine features a 3-bladed crossflow, 9.0 m2 capture area rotor, representing one module of the ORPC RivGen(c) technology. A comprehensive matrix of operational trials was performed to characterize the turbine hydrodynamic performance and the efficiency of the power conversion system. An advanced blade structural monitoring equipment based on fiber-optics strain sensors was implemented and validated. The full-scale turbine tests were carried out at the hydrodynamics testing infrastructure at the Institute of Marine Engineering of the Italian National Research Council (CNR-INM). This facility, among the largest of its kind globally, provided fully controlled and repeatable conditions that allowed to deliver a high-quality dataset on system performance and realiability, contributing to develop new knowledge for the enhancement of hydrokinetic turbine technology.

Wangtun Yang, Yang Zhang, Heng Zhang et al.

This article presents an integrated approach for superpixel segmentation (SPS) and classification, leveraging a deep learning (DL) method tailored to high-resolution remote sensing imagery (RSI). The main contributions of this method include designing a SPS approach based on a convolution-based network architecture that directly predicts superpixels on a regular grid, while adding a classification branch that leverages SPS to classify individual superpixels. The proposed method introduces a dynamic adaptive quantization framework and bit mapping modules, enabling the model to flexibly adapt to various bit-width configurations. End-to-end training integrates SPS and classification tasks within the same deep neural network. Comprehensive experiments utilized RSI datasets across three typical scenes: urban, suburban, and agricultural-pastoral areas. Quantitative and qualitative results confirm the superiority for both SPS and semantic segmentation tasks, showing strong potential for scene understanding and land cover classification. Ablation studies further confirm the efficiency and necessity of various components in the model design. This work provides new ideas and technical support for achieving high-precision, fine-grained interpretation of remote sensing scenes.

Yongming Liu, Shilin Tang, Yuye Huang et al.

Landsat series data (Landsat-5 Thematic Mapper (TM), Landsat-7 Enhanced Thematic Mapper Plus (ETM+), Landsat-8 Operational Land Imager (OLI), and Landsat-9 OLI2) hold significant potential for detecting temporal changes of underwater terrain in optically shallow waters resulting from earthquakes, volcanic eruptions, waves, and human activities due to their extensive time series (nearly 40 years) and medium-spatial-resolution (30 m). However, different Landsat series images have different band sets and signal-to-noise ratios (SNRs) which may impact the consistency of the bathymetry inversion results of optimization-based bathymetry inversion models. Therefore, this study initially quantitatively evaluated the consistency of Landsat series data-derived bathymetry data over the South China Sea, which has a notable distribution of coral islands. The results of 12 images indicated that the root mean square error values of the estimated water depth are generally less than 4 m at Qilian Yu and less than 2 m at Dongsha Dao at depths shallower than 10 m. At depths greater than 10 m, OLI/OLI2 obtained higher accuracy in water depth inversion than did TM/ETM+. The inter-comparison results and temporal results of different geomorphic zones indicated that the Landsat series-derived water depth values in the reef flat and shallow lagoon, where water depth is shallower than 10 m, exhibit high consistency. However, because TM and ETM+ have lower SNRs, for deep lagoons and fore reefs where water depth is greater than 10 m and the substrate is dark, the OLI/OLI2- and TM/ETM+-derived water depth values substantially differ. Then, Landsat series data were applied to detect bathymetric changes in the Nanwei Dao. The temporal results of Nanwei Dao show that the depth of the new port has increased from approximately 2.00 to 10.00 m, whereas the new land in the northeast region has changed from a depth of approximately 7.50 m to land. To date, approximately 584252.74 ± 228884.43 m3 of sediment has been excavated in the port area of Nanwei Dao, with 1010657.21 ± 897737.97 m3 of land reclaimed from the water. Overall, the Landsat series data can be used to detect temporal changes in the underwater terrain of coral islands in the range of approximately 0 to 10 m over the South China Sea for nearly 40 years, and achieving reliable 40-year long-term monitoring of water depths exceeding 10 m remains challenging.

Jiajun Yao, Lulin Cen, Minyu Zheng et al.

Under global warming, persistent extreme heat events (PHEs) in China have increased significantly in both frequency and intensity, posing severe threats to agriculture and socioeconomic development. Combining observational analysis (1961–2019) and numerical simulations, this study investigates the distinct impacts of Northwest Pacific (NWP) and North Atlantic (NA) sea surface temperature (SST) anomalies on PHEs over China. Key findings include the following: (1) PHEs exhibit heterogeneous spatial distribution, with the Yangtze-Huai River Valley as the hotspot showing the highest frequency and intensity. A regime shift occurred post-2000, marked by a threefold increase in extreme indices (+3σ to +4σ). (2) Observational analyses reveal significant but independent correlations between PHEs and SST anomalies in the tropical NWP and mid-high latitude NA. (3) Numerical experiments demonstrate that NWP warming triggers a meridional dipole response (warming in southern China vs. cooling in the north) via the Pacific–Japan teleconnection pattern, characterized by an eastward-retreated and southward-shifted sub-tropical high (WPSH) coupled with an intensified South Asian High (SAH). In contrast, NA warming induces uniform warming across eastern China through a Eurasian Rossby wave train that modulates the WPSH northward. (4) Thermodynamically, NWP forcing dominates via asymmetric vertical motion and advection processes, while NA forcing primarily enhances large-scale subsidence and shortwave radiation. This study elucidates region-specific oceanic drivers of extreme heat, advancing mechanistic understanding for improved heatwave predictability.

Mustafa Açıkkar, Baran Aydın

The present study proposes a deep learning model based on Long-Short Term Memory (LSTM) that uses gage measurements for prediction of landslide-driven maximum tsunami run-up. In an attempt to overcome the limitation of insufficient real-world data in the field, our methodology refers to analytical models to create a comprehensive dataset employing a time series recorded from an offshore gage as input and its corresponding maximum run-up at the shoreline as output, for different landslide scenarios with pre-determined parameters. The LSTM-based model is then trained using this dataset in order to predict the maximum run-up. The results, with mean values of 0.211 m, 0.149 m, 1.745% and 0.9988 for RMSE, MAE, MAPE and R2, respectively, indicate that our model is both accurate and precise. As the data-driven models such as the one proposed here are often utilized to identify relationships that may not be immediately apparent from the physical models alone, our interdisciplinary approach has the potential to foster the development of innovative solutions and methodologies for addressing complex natural hazards by enhancing early warning systems, preparedness and response to tsunamis.

Li Zhou, Runxin Xu, Jiayi Bian et al.

Collisions between ships and sea ice pose a significant threat to maritime safety, making it essential to detect sea ice and perform safety-oriented path planning for polar navigation. This paper utilizes an optimized You Only Look Once version 5 (YOLOv5) model, designated as YOLOv5-ICE, for the detection of sea ice in satellite imagery, with the resultant detection data being employed to input obstacle coordinates into a ship path planning system. The enhancements include the Squeeze-and-Excitation (SE) attention mechanism, improved spatial pyramid pooling, and the Flexible ReLU (FReLU) activation function. The improved YOLOv5-ICE shows enhanced performance, with its mAP increasing by 3.5% compared to the baseline YOLOv5 and also by 1.3% compared to YOLOv8. YOLOv5-ICE demonstrates robust performance in detecting small sea ice targets within large-scale satellite images and excels in high ice concentration regions. For path planning, the Any-Angle Path Planning on Grids algorithm is applied to simulate routes based on detected sea ice floes. The objective function incorporates the path length, number of ship turns, and sea ice risk value, enabling path planning under varying ice concentrations. By integrating detection and path planning, this work proposes a novel method to enhance navigational safety in polar regions.

Hannah I. Sinigaglio, Janusz Murakowski, Dennis W. Prather

For many years, microwave radiometers (MWRs) have contributed to the accuracy of atmospheric models, which are used for weather forecasting and climate-change monitoring. In this work, a new MWR architecture is proposed that utilizes the advantages of photonics to measure a wide swath of microwave spectrum from 50 to 70 GHz. An optical-fiber-based arrayed waveguide grating is used to optically process the spectral content from a V-band radio front end. The result is a radiometer that measures the microwave spectrum near the 60 GHz oxygen absorption peak. The instrument described in this work is shown to produce brightness temperature spectra that fit with expected trends for given weather conditions and has a noise equivalent delta temperature of 0.68 K for an integration time of 8.8 s. The microwave-photonic approach to radiometry offers the capability to measure wider spectral bands than accessible using conventional means, and to probe currently unobserved frequencies, within a reasonable form-factor. Further development of the approach outlined in this work will lead to a space-worthy MWR for improved spectral coverage of atmospheric measurements.

CHEN Nü, XU Wenhao, WU Biao, CHEN Xiaowen, HOU Dongwei

In order to investigate the evolution of pore structures in cementitious materials, a statistical model is proposed by taking the cement paste as a random dispersion system of two-phase medium. Simultaneously, the μic platform is employed to simulate the cement hydration. The results obtained from the simulation and the disperse models are compared with each other, and further analysis on calculation conditions and parameters of the disperse models are conducted. The pore size distribution obtained from polydisperse hard sphere model is very close to the simulation in completely dispersion condition. Taking into account the cross and agglomeration effects of hydrated products, the calculation results of the monodisperse concentric-shell model are more consistent to the simulations. Considering the flocculation of cement particles in initial state, the monodisperse hard model is closer to the simulation results. This paper offers a new insight from the viewpoints of mathematics and physics to understand and describe the pore structures of cementitious materials.

Mengxiang Li, Guo Wang, Kun Liu et al.

The safety assessment of ship cargo securing systems is of significant importance in preventing casualties, vessel instability, and economic losses resulting from the failure of securing systems during transportation in adverse sea conditions. In this study, an independently designed cylindrical cargo securing scheme with supporting structures was adopted for investigation. Utilizing a sway device, three-degree-of-freedom coupled motion encountered during ship transportation was obtained, and data regarding changes in the support forces at the foundations and tension forces in the lashing ropes were collected. Subsequently, numerical simulations were conducted using the multibody dynamics software ADAMS 2020. The results obtained from the simulations were compared with the experimental data. The overall tendencies were accurately predicted in the numerical analysis. It was observed that the difference of the peak support forces between the numerical simulation results and the experimental data were within a 10% margin. In terms of the lashing ropes, the difference was limited, within 9%. These findings demonstrate that numerical simulation techniques can provide valuable insights for verifying the safety of practical cargo securing systems.

Zhang Wanchao, Zhu Yang, Liu Shuxu et al.

To obtain the mechanical energy of waves from arbitrary directions, the vibration absorbers of wave energy converters (WEC) are usually vertically axisymmetric. In such case, the wave-body interaction hydrodynamics is an essential research topic to obtain high-efficiency wave energy. In this paper, a semi-analytical method of decomposing the complex axisymmetric boundary into several ring-shaped stepped surfaces based upon the boundary approximation method (BAM) is introduced and examined. The hydrodynamic loads and parameters, such as the wave excitation forces, added mass and radiation damping of the vertical axisymmetric oscillating buoys, can then be achieved by using the new boundary discretisation method. The calculations of the wave forces and hydrodynamic coefficients show good convergence with the number of discretisation increases. Comparison between the constringent results and the results of the conventional method also verifies the feasibility of the method. Then, simulations and comparisons of the hydrodynamic forces, motions and wave power conversions of the buoys with series draught and displacement ratios in regular and irregular waves are conducted. The calculation results show that the geometrical shape has a great effect on the hydrodynamic and wave power conversion performance of the absorber. In regular waves, though the concave buoy has the lowest wave conversion efficiency, it has the largest frequency bandwidth for a given draught ratio, while in irregular waves, for a given draught ratio, the truncated cylindrical buoy has the best wave power conversion, and for a given displacement of the buoy, the concave buoy shows the best wave power conversion ability.

Alessandro Zambon, Lorenzo Moro, Jeffrey Brown et al.

Polar navigation entails challenges that affect the continuation of ship operations in severe ice conditions. Due to ice-propeller interaction, propulsion shafting segments are often at a high risk of failure. Efficient methods for shaft line design are hence needed to ensure the safety of ice-going vessels and propulsion reliability. To this end, full-scale measurements have proven essential to support the development of ship-design tools and updated safety regulations for ice-going vessels. This paper presents a unique integrated measurement system that employs measuring equipment to monitor Polar-Class vessel performance and shaft line dynamics during ice navigation. The system was installed on board the Canadian Coast Guard (CCG) icebreaker Henry Larsen. This experimental concept aims to monitor the shaft’s torque and thrust fluctuations during ice navigation to obtain information about the ship’s propulsion efficiency. In the paper, we describe the arrangement of the measurement system and the components it features. Finally, we present preliminary datasets acquired during two icebreaking expeditions. This work is framed into a broader research project, which includes the long-term objective to determine a correlation between sea ice conditions and the dynamic response of shaft lines.

Jihong Ye, Yiyang Fang, Xinxiang Yang

The integrity of oil pipelines has received considerable attention. Pipeline leakage accidents cause environmental pollution and casualties. Analysis of accident data in recent years shows that the harbor oil pipeline is prone to natural disasters such as typhoons. The vulnerability analysis of the pipeline was conducted from three perspectives: typhoon grades, windward angles, and operating conditions. The analytic hierarchy is used to build the vulnerability evaluation index system. The vulnerability evaluation score of the pipeline can be calculated by the semi-quantitative method. The results show that the probability of pipeline vulnerability failure increases with the increase of typhoon level, while the change of wind angle has no obvious effect on the pipeline. The full load of the pipeline has a higher evaluation score than that of the empty load, which means the full load is safer. The vulnerability analysis of oil pipelines can effectively improve the safety of pipeline transportation under the influence of typhoons.

Zhixuan Tang, Jiangbing Qiu, Guixiang Wang et al.

Gymnodimine-A (GYM-A) is a fast-acting microalgal toxin and its production of certified materials requires an efficient harvesting technology from the large-scale cultures of toxigenic microalgae. In this study the recoveries of GYM-A were compared between several liquid-liquid extraction (LLE) treatments including solvents, ratios and stirring times to optimize the LLE technique for harvesting GYM-A from <i>Karenia selliformis</i> cultures, of which the dichloromethane was selected as the extractant and added to microalgal cultures at the ratio 55 mL L⁻¹ (5.5%, <i>v</i>/<i>v</i>). The recovery of GYM-A obtained by the LLE technique was also compared with filtration and centrifugation methods. The stability of GYM-A in culture media were also tested under different pH conditions. Results showed that both the conventional filter filtration and centrifugation methods led to fragmentation of microalgal cells and loss of GYM-A in the harvesting processes. A total of 5.1 µg of GYM-A were obtained from 2 L of <i>K. selliformis</i> cultures with a satisfactory recovery of 88%. Interestingly, GYM-A obviously degraded in the culture media with the initial pH 8.2 and the adjusted pH of 7.0 after 7 days, but there was no obvious degradation in the acidic medium at pH 5.0. Therefore, the LLE method developed here permits the collection of large-volume cultures of <i>K. selliformis</i> and the high-efficiency extraction of GYM-A. This work provides a simple and valuable technique for harvesting toxins from large-scale cultures of GYM-producing microalgae.

Bo Zhu, Weiping Huang, Xinglong Yao et al.

The rigid body swing is an important problem for steel catenary risers (SCRs). In addition to many other important issues, the transverse flow direction response is studied in this paper. By extending the load terms of the large deflection slender beam equation, the load of suspension point in the z direction, Morison and rigid body swing are superimposed on the beam equation. On the basis of the above work, a Cable3d subroutine is written to complete the task. Then the structural response is simulated and verified by the Lissajous phenomenon and spectral phase analysis. On the basis of verification, the response is analyzed from an angle of three-dimensional space and the influence coefficient is adopted to evaluate the effect of rigid body swing. The importance of loads is determined by spectral analysis. Phase curve and the change of vibration direction are analyzed by higher orders of frequency. The results show the verification of Lissajous and spectral phase analysis are feasible. The analysis of the spatial response shows the vibration direction of the 140th node is in the same direction as the rigid body swing vector, so the interaction is relatively of more intensity and the influence coefficient is relatively larger. This influence interval of rigid body swing displacement statistical analysis is &minus;0.02 to 0.02 and the effect is weak. The spectrum analysis indicates there is no resonance between the main load and the bending vibration, and the analysis also shows the main influence load of the transverse flow response in this paper is the top load in the z direction. According to phase analysis, the load has a high order effect on the spectral phase curve of the structure. This paper has drawn a conclusion that rigid body swing has limited effect on transverse flow response, however, it has a relatively strong impact on the middle region of the riser, so it plays an influential role on the safety of the riser to some extent. The key point for this paper is to provide qualitative standards for the verification of rigid body swing through Lissajous graphs, which are central factors to promote the development of rigid body swing. It is hoped that the above research can provide some reasonable suggestions for the transverse flow response simulation of the steel catenary riser.

G. Wei, G. Wei, X. Zhang et al.

<p>Evapotranspiration (ET) is a major component of the land surface process involved in energy fluxes and energy balance, especially in the hydrological cycle of agricultural ecosystems. While many models have been developed as powerful tools to simulate ET, there is no agreement on which model best describes the loss of water to the atmosphere. This study focuses on two aspects, evaluating the performance of four widely used ET models and identifying parameters, and the physical mechanisms that have significant impacts on the model performance. The four tested models are the Shuttleworth–Wallace (SW) model, Penman–Monteith (PM) model, Priestley–Taylor and Flint–Childs (PT–FC) model, and advection–aridity (AA) model. By incorporating the mathematically rigorous thermodynamic integration algorithm, the Bayesian model evidence (BME) approach is adopted to select the optimal model with half-hourly ET observations obtained at a spring maize field in an arid region. Our results reveal that the SW model has the best performance, and the extinction coefficient is not merely partitioning the total available energy into the canopy and surface but also including the energy imbalance correction. The extinction coefficient is well constrained in the SW model and poorly constrained in the PM model but not considered in PT–FC and AA models. This is one of the main reasons that the SW model outperforms the other models. Meanwhile, the good fitting of SW model to observations can counterbalance its higher complexity. In addition, the detailed analysis of the discrepancies between observations and model simulations during the crop growth season indicate that explicit treatment of energy imbalance and energy interaction will be the primary way of further improving ET model performance.</p>

Banfu Yan, Qiqi Zou, You Dong et al.

A lightweight composite bridge deck system composed of steel orthotropic deck stiffened with thin Ultra-High Performance Concrete (UHPC) layer has been proposed to eliminate fatigue cracks in orthotropic steel decks. The debonding between steel deck and UHPC layer may be introduced during construction and operation phases, which could cause adverse consequences, such as crack-induced water invasion and distinct reduction of the shear resistance. The piezoelectric lead zirconate titanate (PZT)-based technologies are used to detect interfacial debonding defects between the steel deck and the UHPC layer. Both impedance analysis and wave propagation method are employed to extract debonding features of the steel-UHPC composite slab with debonding defect in different sizes and thicknesses. Experimental tests are performed on two steel-UHPC composite slabs and a conventional steel-concrete composite deck. Additionally, an improved Particle Swarm Optimization (PSO)-k-means clustering algorithm is adopted to obtain debonding patterns based on the feature data set. The laboratory tests demonstrate that the proposed approach provides an effective way to detect interfacial debonding of steel-UHPC composite deck.

Rachel M. Wilson, Reny B. Tyson, James A. Nelson et al.

Two groups of common bottlenose dolphins (Tursiops truncatus) have been identified within St. George Sound, Florida, USA: high site-fidelity individuals (HSF) which are individuals sighted multiple times in the region (i.e., ≥2 months, ≥2 seasons, and ≥2 years), and low site-fidelity individuals (LSF), which are individuals sighted fewer than 2 months, in 2 different seasons among 2 different years. Our goal was to determine whether differences in foraging behaviors were correlated with differences in sighting frequency and overall usage of St. George Sound by the two groups. We used carbon, nitrogen, and sulfur stable isotopes and niche hypervolume metrics to model the foodweb of St. George Sound. Mixing model results indicated that croaker, mojarra, pigfish, pinfish, and silverperch were the most important prey items for dolphins. The hypervolume metrics demonstrate niche partitioning between HSFs and LSFs, with the HSFs relying more heavily on pinfish, pigfish, and mojarra, while the LSFs relied more on silverperch. Plankton, benthic diatoms, seagrass, and epiphytes all contributed to secondary production within St. George Sound. This diversity of source utilization by seagrass-associated consumers supported by a high rate of total production likely sustains high secondary productivity despite the potential for competition in this system. Zooplankton was the most important basal source to the system, followed by seagrass and benthic primary production (as indicated by a sanddollar proxy). The reliance of dolphins on seagrass-dependent prey indicates that alteration of seagrass habitat would significantly impact the dolphin community foraging in St. George Sound and suggests that preservation of seagrass habitat is an important component of an effective management strategy for dolphin populations in the region.