Facilitated by recent establishment of terrestrial networks and satellite constellations of Automatic Identification System (AIS) receivers, ship trajectories are becoming increasingly available and the size of recorded trajectories is getting larger. Large sets of trajectories create problems of storing, transmitting and processing data. Using appropriate methods, an accurate representation of the original trajectories can be obtained by compressing redundant information, while maintaining the main characteristic elements. In this paper, a new scheme and the implementation of the Douglas-Peucker (DP) algorithm are presented, which can simplify AIS trajectories by extracting characteristic points. As for the simplification threshold, the solo parameter of the DP algorithm, a new AIS-based minimum ship domain evaluation method is proposed and acts as criteria for simplification threshold determination. Finally, a validation is made to examine the effectiveness of the DP simplification algorithm and the rationality of the simplification threshold. The result indicates that the DP algorithm can simplify AIS trajectories effectively; the simplification threshold is scientific and reasonable.
Facilitated by the establishment of terrestrial networks and satellite constellations of Automatic Identification System (AIS) receivers, large quantities of spatial and temporal information that trace ships' paths have been collected. The exponential increase in the amount of AIS data has caused expensive and time-consuming transmission, calculation and storage problems. Using appropriate trajectory simplification methods in a timely manner to compress redundant information while minimising the loss of importation information is important. To minimise the simplification error, this paper proposes an online multi-dimensional simplification algorithm for AIS trajectory streaming data. The simplification algorithm takes into account position, direction and speed preservation. Finally, a comparison experiment with other algorithms is made to examine the effectiveness of this algorithm. The results indicate that the proposed online multi-dimensional simplification algorithm can effectively preserve a ship's motion state, including its position, speed and course.
In order to reduce the possibility of crew suffering from various injuries, quantitative marine individual risk model is adopted to improve the original Risk Matrix. Improved Risk Matrix quantizes the limit frequency and injurious consequences corresponding to the severity of the accident, thereby it reduces the ambiguity of Risk Matrix. Using the falling accident as example, this paper demonstrates the establishment of improved Risk Matrix for enterprise risk control.
The reacting flow fields of a bluff-body combustor and a newly devised cap burner were investigated. To understand the flame structure, methods based on particle image velocimetry (PIV) and chemiluminescence were adopted to detect the flow structure and local intensity of flame radiation, either individually or synchronically. In addition, the distribution of temperature was obtained by thermocouple measurement. In the study for a bluff-body burner, the flame pattern, with increasing central fuel-jet velocity at fixed annular air-flow velocity, was classified into three modes: recirculating flame, jet-dominated flame, and jet-like flame. The position of flame front was dependent on the flow field. When the velocity of fuel jet was increased, the recirculation zone became shrunk and in turn affected the formation of combustion region. The temperature profiles showed that the recirculation zone provided a heat source for downstream flow and the ignition was facilitated by the recirculating flow. In the study for the cap burner, the flammable limit indicated an expanded range of fuel jet velocity. This was due to the stabilization and induced near-premixing effects of the cap. The experimental results were compared with numerical simulations. The distributions of velocity, temperature, and specific radicals like CH and OH can thus be studied in depth. This reveals advantages of the cap device over the traditional burners and direction for further improvement of the structure that can significantly enhance the mixing process and combustion efficiency. NomenclatureD j = mass diffusivity P = pressure T = temperature U = flow velocity U j = central fuel jet velocity U a = annular air flow velocity = fluid density = surface tension of liquid = fluid viscosity
Abstract. As the mainstream wireless LAN technology, Wi-Fi can achieve fast data transfer. With the subway moving in a high speed, video data transmission between the metro and the ground is achieved through Wi-Fi technology. This paper aims at solving the Caton problem caused by switching packet loss in the process of playing real-time video on the train terminal, and proposes matrix-type packet loss compensation scheme. Finally, the feasibility of the scheme is verified by experiments.
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