An Improved A-Star Algorithm Considering Water Current, Traffic Separation and Berthing for Vessel Path Planning

A traditional A-Star (A*) algorithm generates an optimal path by minimizing the path cost. For a vessel, factors of path length, obstacle collision risk, traffic separation rule and manoeuvrability restriction should be all taken into account for path planning. Meanwhile, the water current also plays an important role in voyaging and berthing for vessels. In consideration of these defects of the traditional A-Star algorithm when it is used for vessel path planning, an improved A-Star algorithm has been proposed. To be specific, the risk models of obstacles (bridge pier, moored or anchored ship, port, shore, etc.) considering currents, traffic separation, berthing, manoeuvrability restriction have been built firstly. Then, the normal path generation and the berthing path generation with the proposed improved A-Star algorithm have been represented, respectively. Moreover, the problem of combining the normal path and the berthing path has been also solved. To verify the effectiveness of the proposed A-Star path planning methods, four cases have been studied in simulation and real scenarios. The results of experiments show that the proposed A-Star path planning methods can deal with the problems denoted in this article well, and realize the trade-off between the path length and the navigation safety

Ship heading control based on backstepping and Least squares support vector machine

In this paper, a least squares support machine (LS-SVM) and backstepping process based method is proposed to control a ship’s heading. In the method, the control object is set up the response model, which could consider the delay of the ship’s steering gear. Firstly, a feedback controller is designed by backstepping, and a feedforward inverse controller is trained by LS-SVM. Then the backstepping method and LS-SVM inverse model are combined to form a new controller by adapting their output weights. Finally, simulations using only the backstepping method are compared with different interferences to verify the effectiveness of the combined controller proposed in this paper

Improved buoyancy-driver hybrid ventilation system for multiple-heat-source industrial buildings

An industrial building may have several heat sources which together create a high-temperature working environment that puts the health of workers at risk. Ventilation is an effective way to remove heat, but improperly designed systems may fail to create a healthy thermal environment. The performance of buoyancy-driven hybrid ventilation in a multi-heat-source industrial plant was investigated in this study. The effects of the height of the inlet above the floor and exhaust velocity on the hybrid ventilation performance were studied; properly increasing the above-floor inlet height appears to improve the thermal environment while excessive mechanical exhaust velocity leads to increased energy consumption with a negative impact on ventilation efficiency. The optimum parameters of the improved ventilation system were determined and compared against existing ventilation systems. In summer, the improved ventilation system shows an average temperature of 34.61 °C, which is 3.40 °C lower than the existing system. The allowed exposure time (AET) is 52 min, which is 18 min longer than the existing system. In winter, the improved ventilation system shows an average temperature of 18.68 °C, which meets the design requirements for industrial buildings. The improved ventilation system can provide thermally comfortable conditions in both summer and winter

Field and Wind Tunnel Experiments of Wind Field Simulation in the Neutral Atmospheric Boundary Layer

To investigate the pollutant dispersion of a nuclear power plant, a field tracing experiment was carried out in neutral stratification weather with the main wind direction SSW. On this basis, a wind speed profile and turbulence intensity profile consistent with the site were created in the wind tunnel. Meanwhile, how to generate a wind field of neutral stratification in a wind tunnel was studied in detail. Finally, a 1:1000 nuclear power area model was made to conduct tracing experiments in the wind tunnel. The results show that when the horizontal and vertical distances of the spire are 300 mm and 500 mm, and the horizontal and vertical distances of the rough element are 250 mm and 500 mm. A wind speed profile with a wind profile index of 0.321 was generated in the wind tunnel (0.334 in the field test), and the wind tunnel tracer experiment had the same diffusion trend as the field, which verified the accuracy of the flow field

Field and Wind Tunnel Experiments of Wind Field Simulation in the Neutral Atmospheric Boundary Layer

To investigate the pollutant dispersion of a nuclear power plant, a field tracing experiment was carried out in neutral stratification weather with the main wind direction SSW. On this basis, a wind speed profile and turbulence intensity profile consistent with the site were created in the wind tunnel. Meanwhile, how to generate a wind field of neutral stratification in a wind tunnel was studied in detail. Finally, a 1:1000 nuclear power area model was made to conduct tracing experiments in the wind tunnel. The results show that when the horizontal and vertical distances of the spire are 300 mm and 500 mm, and the horizontal and vertical distances of the rough element are 250 mm and 500 mm. A wind speed profile with a wind profile index of 0.321 was generated in the wind tunnel (0.334 in the field test), and the wind tunnel tracer experiment had the same diffusion trend as the field, which verified the accuracy of the flow field

A Visual Analysis Approach to Understand and Explore Quality Problems of AIS Data

Low quality automatic identification system (AIS) data often mislead analysts to a misunderstanding of ship behavior analysis and to making incorrect navigation risk assessments. It is therefore necessary to accurately understand and judge the quality problems in AIS data before a further analysis of ship behavior. Outliers were filtered in the existing methods of AIS quality analysis based only on mathematical models where AIS data related quality problems are not utilized and there is a lack of visual exploration. Thus, the human brain’s ability cannot be fully utilized to think visually and for reasoning. In this regard, a visual analytics (VA) approach called AIS Data Quality visualization (ADQvis) was designed and implemented here to support evaluations and explorations of AIS data quality. The system interface is overviewed and then the visualization model and corresponding human-computer interaction method are described in detail. Finally, case studies were carried out to demonstrate the effectiveness of our visual analytics approach for AIS quality problems

Model predictive ship collision avoidance based on Q-learning beetle swarm antenna search and neural networks

Real-time collision avoidance with full consideration of ship maneuverability, collision risks and International Regulations for Preventing Collisions at Sea (COLREGs) is difficult in multi-ship encounters. To deal with this problem, a novel method is proposed based on model predictive control (MPC), an improved Q-learning beetle swarm antenna search (I-Q-BSAS) algorithm and neural networks. The main idea of this method is to use a neural network to approximate an inverse model based on decisions made with MPC for collision avoidance. Firstly, the predictive collision avoidance strategy is established following the MPC concept incorporating an I-Q-BSAS algorithm to solve the optimization problem. Meanwhile, the relative collision motion states in typical encounters are collected for training an inverse neural network model, which is used as an approximated optimal policy of MPC. Moreover, to deal with uncertain dynamics, the obtained policy is reinforced by long-term retraining based on an aggregation of on-policy and off-policy data. Ship collision avoidance in multi-ship encounters can be achieved by weighting the outputs of the neural network model with respect to different target ships. Simulation experiments under several typical and multi-ship encounters are carried out using the KVLCC2 ship model to verify the effectiveness of the proposed method.Accepted Author ManuscriptTransport Engineering and Logistic

Interface engineering of Fe-Co3N/CoP composite with N-doped C by using soybean: Fabrication of efficient electrocatalysts for oxygen evolution reaction

Soybean can serve as an efficient carbon and nitrogen source for in-situ fabrication of efficient composite electrocatalysts with conductive nitrogen-doped carbon (N-C) material. In this study, the iron-doped cobalt nitride/phosphide (Fe-Co3N/CoP) nanosheet was composited with a conductive N-C material by using soybean as C and N source, as well as NH3 as additional nitrogen source. During the nitridation process of Fe-Co3N, N-C bond was formed as a newly generated Co(Fe)-N-C active sites. Therefore, it fabricates a good microscopic contact interface between the catalyst and carbon material for charge transfer. Besides, the introduction of Fe-CoP by partially phosphating Fe-Co3N further improved the OER activity due to the high catalytic activity of Co sites with high valence state. As a result, the obtained electrocatalyst exhibited overpotentials as low as 285 and 390 mV for supporting 10 and 100 mA/cm−2 current densities. This work indicates that the design of materials with good interfaces could be an effective approach for the preparation of electrocatalysts for water electrolysis

Dark Current Characteristic of p-i-n and nBn MWIR InAs/GaSb Superlattice Infrared Detectors

The theoretical dark current model of InAs/GaSb type II superlattice (T2SL) p-i-n and nBn photodetectors is presented. The nBn structure was designed to suppress generation-recombination (G-R), surface leakage and tunnel currents. 8 band k p model including the conduction and valence band mixing was applied to calculate the band structure and optical transition of InAs/GaSb T2SL. Theoretical calculations are performed for different doping level of p-i-n and nBn detectors. For p-i-n detector, dark current was studied for different p-contact layer doping and different absorber layer doping. For nBn detector, different contact doping concentration and absorb doping concentration was studied. At low temperature, dark current of p-i-n detector was dominant by generation-recombination and tunnel current, nBn structure can inhibit tunnel and generation-recombination current. At high temperature, the dark current of p-i-n detector and nBn detector have the same order of magnitude and are both dominated by diffusion current. Quantum efficiency and resistance-area product of p-i-n and nBn detectors were also calculated at 120 K, quantum efficiency of p-i-n detector is a bit larger than nBn detector, but dark current and resistance area product of nBn detector are better