Cooperative hunting of multi-autonomous underwater vehicle (AUV) is an important research topic. Current studies concentrate on AUVs with the same speed abilities and mostly do not consider their ...speed differences. In fact, AUVs in a hunting group are often of different types and possess different maximum sailing speeds. For inhomogeneous multi-AUV, a novel time competition mechanism is proposed to construct an efficient dynamic hunting alliance. Hunting team with AUVs possessing higher speed abilities is more suitable for the vast underwater environment. In the pursuing stage, AUV needs to act fast enough to avoid the escape of evader. To achieve a quick and accurate pursuit, a combined path planning approach is presented, which combines a Glasius bio-inspired neural network model and a belief function. Simulation experiments demonstrate the feasibility and efficiency of the proposed algorithm in the cooperative hunting of inhomogeneous multi-AUV under dynamic underwater environment with intelligent evaders and multi-obstacle.
The call for green shipping is increasing, and the reduction of greenhouse gas emissions from ships becomes more and more important. Traditional ship energy efficiency monitoring is based on the noon ...reports, which are susceptible to human error and have a time delay. Many ship energy efficiency monitoring systems have been designed and developed, but they usually cannot send data to the shore in time. In order to identify abnormal fuel consumption in time, this paper realizes a big data collection system for ship energy efficiency monitoring based on the BeiDou System. The system installed on two sister container ships has already collected a lot of data. Big data analysis methods, such as principal component analysis (PCA) and correlation analysis, are applied in the system to realize data visualization and analysis. Using PCA, it turns out that the shaft power of the main engine is related to a certain ship speed, which is also affected by load and weather conditions, and is the biggest factor in determining fuel consumption. To realize the assessment of hull fouling and the optimization of ship trim, a useful physics-based analysis is proposed. The analysis shows that the fouling of ship body greatly increases its resistance. Our analysis method can also find the best trim under specific loading condition. All these points are important for reducing fuel consumption and improving ship efficiency.
•A case study from subtropic China indicates the in-situ provenance of peat brGDGTs.•Global comparison indicates the in-situ provenance of brGDGTs in most peatlands.•Possible different origins of ...brGDGTs in cold/alkaline and other peatlands.•In most peatlands, brGDGTs reliably record local environmental changes.
Sedimentary branched glycerol dialkyl glycerol tetraethers (brGDGTs) have been proposed as indicators of environmental change for more than a decade. However, the origin of brGDGTs in terrestrial sediments is a fundamental issue affecting their use in paleoenvironmental reconstruction. Although peat sediments are one of the best terrestrial archives for paleoclimatic studies, the origin of brGDGTs in peat sediments remains poorly constrained. Here, we report the results of a study of brGDGTs in peat surface sediments, peat core sediments, and in the surrounding surface soils of the Shiwangutian (SWGT) peatland in southern China. Comparison of the molecular distributions and absolute concentrations of the total brGDGTs extracted from these different sample types reveals the dominant in-situ origin of the brGDGTs in the SWGT peatland. We then compare the results from globally-distributed surface peat sediments and surface soils, which confirms the dominant in-situ provenance of brGDGTs at almost all of the studied peatlands. Furthermore, in specific environments, such as in peatlands in cold and alkaline environments, the origin of brGDGTs could be different to that in other environments. Our results provide fundamental evidence for the provenance of brGDGTs in peat sediments, with relevance for peat-brGDGTs-based paleoclimatic reconstructions.
Under the recent background of ‘Green Shipping’ and rising fuel prices, it is very important to reduce the fuel consumption rate of ships, which is directly affected by the performance of the main ...engine. A reasonable maintenance schedule can optimise the performance of the main engine. However, a traditional maintenance schedule is based on the navigation distance and time, ignoring many other factors, such as a harsh working environments and frequently changing operating conditions, which will lead to faster performance degradation. In this study, a real-time evaluation method combing big data of ship energy efficiency with physics-based analysis is proposed to judge the degradation of main engine performance and assist in determining the maintenance schedule. Firstly, based on the developed ship energy efficiency big data platform, the distribution statistics and comparison of different operating states are carried out. Gaussian mixture model (GMM) and Density-Based Spatial Clustering of Applications with Noise (DBSCAN) are used to cluster the data and the high-density data areas are obtained as the analysis points. Then, the data of the analysis points are polynomial fitted, by the least square method, to obtain the propulsion characteristics curves, load characteristic curves, and speed characteristic curves, which can be used to observe the performance degradation of the main engine. The results show that this method can effectively monitor the degradation degree of the main engine performance, and is of great significance to fuel efficiency improvements and greenhouse gas (GHG) emissions reduction.
With the rapid developments of marine resource exploitation, mounts of marine engineering equipment are settled on the ocean. When it is not possible to move the damaged equipment into a dry dock, ...welding operations must be performed in underwater environments. The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment. The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique. First, we elaborated recent advances and key issues of drainage nozzles all over the world. Next, we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials. Then, the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed. The differences between the convection, conduction, and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated. After that, several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed. Finally, suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided. The present review will not only enrich the knowledge in the underwater repair technology, but also provide important guidance for the potential applications of the technology on the marine engineering.
Path planning for autonomous underwater vehicles (AUVs) is a key research focus in the marine domain, requiring consideration of the underwater environment's complexity and the efficiency of the ...planning algorithms. Firstly, a variety of strategies such as the memory function are integrated into the artificial jellyfish search algorithm (JS) to improve its convergence accuracy, and the improved artificial jellyfish search algorithm (IJS) is obtained. Secondly, this paper establishes a good objective function including the ocean current disturbance model, which helps the IJS algorithm better plan the paths to avoid obstacles and strong side currents. Furthermore, the optimal smoothed paths are obtained by using a cubic spline midpoint interpolation method. Finally, multiple simulation experiments are performed on the multi-obstacle ocean current model with realistic terrain data. The comparison results show that the IJS algorithm with a short running time has the optimal time cost and ocean current penalty cost for the planned path. In addition, the IJS algorithm is also shown to be adaptable in the field of multi-AUV movements.
Abstract
Energy band alignment theory has been widely used to understand interface charge transfer in semiconductor/semiconductor heterojunctions for solar conversion or storage, such as quantum-dot ...sensitized solar cells, perovskite solar cells and photo(electro)catalysis. However, abnormally high open-circuit voltage and charge separation efficiency in these applications cannot be explained by the classic theory. Here, we demonstrate a Faradaic junction theory with isoenergetic charge transfer at semiconductor/semiconductor interface. Such Faradaic junction involves coupled electron and ion transfer, which is substantively different from the classic band alignment theory only involving electron transfer. The Faradaic junction theory can be used to explain these abnormal results in previous studies. Moreover, the characteristic of zero energy loss of charge transfer in a Faradaic junction also can provide a possibility to design a solar conversion device with a large open-circuit voltage beyond the Shockley-Queisser limit by the band alignment theory.
Recent syntheses of marine paleoclimate records have revealed an overall long-term Holocene warming trend, especially in mean annual temperature (MAT), which is inconsistent with most terrestrial ...records on continental and global scales. We present a record of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from the Shiwangutian (SWGT) peatland in central-southern China. Comparative results from surface peat samples from the SWGT peatland and the surrounding surface soils demonstrate that the brGDGTs are primarily of in-situ origin, demonstrating their potential as a record of local environmental changes. Monthly observational results show no seasonal variations in the methylation index of 5-methyl brGDGTs (MBT'5MEwhich has been proposed as an indicator of local environmental temperature in peatlands) in the surface peat samples, suggesting that it is an indicator of MAT. Thus, we conclude that the long-term increasing trend in the brGDGTs-based MBT'5ME records of two parallel independently-dated peat cores from the SWGT peatland clearly demonstrate a long-term warming trend during the Holocene. Additionally, we found that the brGDGTs-based records from five peatlands along an environmental gradient from southeastern (SE) humid to northwestern (NW) arid China also show a long-term Holocene warming trend. However, this trend is the opposite to the long-term Holocene cooling trend indicated by brGDGTs records from two peatlands in northeastern (NE) China, highlighting the complexity of peat brGDGTs as a climatic indicator. We therefore appeal for more peat brGDGTs studies, which are important for understanding the climate history of the Holocene and its potential relationship with human activities.
•No seasonal bias in MBT'/MBT'5ME indices of the brGDGTs in SWGT surface peats.•Long-term Holocene warming trend in two absolutely dated SWGT peat cores.•Seven peat MBT' records from five peatlands at four locations were composited.•The four locations cover a transect from southeastern to northwestern China.•Long-term Holocene warming trend is indicated by the composite MATpeat record.
In this paper, we improve networks’ spectral efficiency (SE), extend networks’ lifetime, and maximize networks’ energy efficiency (EE) of two-way full-duplex (FD) relay networks. Firstly, to improve ...networks’ SE and to extend networks’ lifetime simultaneously, we design a two-way FD relay transmission strategy with simultaneous wireless information and power transfer and direct links (DLs). The designed transmission strategy can complete a bidirectional communication in only one time slot with the exists of DLs and the energy-constrained relay node. With the designed transmission strategy, we further give the characteristics of relay amplification factor, the analysis of the designed transmission strategy, and the EE analysis of traditional half-duplex two-way amplify-and-forward relaying. Secondly, to maximize networks’ EE, we present both the EE maximization problems and analyses of the designed transmission strategy with equal power allocation and optimal power allocation. To solve the EE maximization problems, we further propose the alternating optimal algorithm and give complexity analysis of the algorithm. Simulations show that our designed transmission strategy can improve the SE and EE of the networks.
Path planning is a prerequisite for autonomous underwater vehicles to perform tasks autonomously. Many shortest distance algorithms are applied, and ocean currents are ignored to plan a short path in ...distance, which is usually time and energy consuming. In fact, the favourable currents can be exploited while avoiding the opposite ocean flows. Based on the bioinspired neural network architecture, this paper proposes a novel dynamic neural network model to plan the time-saving path in ocean current environments. After that, the path is smoothed by the B-spline algorithm. Analysis of the model shows that it can find out the minimum time path. Many simulations have also been introduced to test the effectiveness of the proposed model, showing good results. The dynamic neural network model has no learning procedure and can run in parallel. It has the advantages of loose parameter restrictions and wide spreading of neural activities. In addition, it has also been proven to be suitable for strong ocean currents.
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