Ship trajectory prediction is a key requisite for maritime navigation early warning and safety, but accuracy and computation efficiency are major issues still to be resolved. The research presented ...in this paper introduces a deep learning framework and a Gate Recurrent Unit (GRU) model to predict vessel trajectories. First, series of trajectories are extracted from Automatic Identification System (AIS) ship data (i.e., longitude, latitude, speed, and course). Secondly, main trajectories are derived by applying the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm. Next, a trajectory information correction algorithm is applied based on a symmetric segmented-path distance to eliminate the influence of a large number of redundant data and to optimize incoming trajectories. A recurrent neural network is applied to predict real-time ship trajectories and is successively trained. Ground truth data from AIS raw data in the port of Zhangzhou, China were used to train and verify the validity of the proposed model. Further comparison was made with the Long Short-Term Memory (LSTM) network. The experiments showed that the ship’s trajectory prediction method can improve computational time efficiency even though the prediction accuracy is similar to that of LSTM.
lFloc aggregation (< 200 μm) results in a quick enrichment of AnAOB.lAggregated flocs alter the physio-morphology and microbial community in sludge.lFloc aggregates supply an initial carrier and ...anaerobic microenvironment for AnAOB.lAnAOB rapid enrichment further facilitates anammox granules maturation.
Rapid enrichment of anaerobic ammonia oxidation bacteria (AnAOB) is highly associated with the granulation process; however, the interactive mechanism remains unclear, especially for the initial granulation process. A single-stage partial nitritation-anammox (PN/A) bioreactor combined with granular/floc sludge was operated for 400 days. During the experimental period, the nitrogen removal rate increased from 0.60 to 1.21 kg N m−3d−1, and the nitrogen removal capability improved primarily during a transition period (days 200–250), which was accompanied by a particle size increase and AnAOB proliferation (4.9 ± 1.7 days). Moreover, as observed by the biomass physio-morphology, the size distribution, and the microbial community shift, small flocs (< 200 μm) aggregated due to the addition of excess sodium acetate. The emerging floc aggregates represented an early form of granules, providing the initial biological carrier and necessary anaerobic microenvironment for the growth of attached AnAOB, resulting in a high AnAOB growth-rate. These results are the first direct evidence that floc aggregates are essential to AnAOB enrichment, and that they can be affected by operational conditions. This study provides an in-depth understanding of the link between floc aggregations and AnAOB enrichment and broadens the feasibility of optimizing PN/A applications.
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•Mature macroporous carrier (Mac) biofilms possess larger oxygen loading area.•Mac-biofilms enrich anammox bacteria mainly via partial nitritation/anammox.•Larger anoxic layer avail ...enriching anammox bacteria inside microporous carrier.•Microporous carrier biofilms polish nitrogen mainly via a denitrification/anammox.•Microporous carrier biofilms are more stable with sparse microbial correlations.
In this study, two typical carrier types, microporous and macroporous carriers, were collected from a full-scale partial nitritation/anammox reactor for analysis and comparison of the biofilm structure characteristics, performance and removal nitrogen pathway. For microporous carriers, a thicker biofilm (>5 mm) was obtained with higher biomass and abundance of anammox bacteria as well as a higher nitrogen removal efficiency due to the integration of denitrifying and anammox bacteria. In addition, higher microbial community stability can be expected under varying environmental conditions. In comparison, macroporous carrier biofilm exhibited a lower thickness (0.4–2.3 mm) and lower microbial richness, with a strong network correlation among genera. Analysis showed that the mainly positive correlation between anammox bacteria and ammonium oxidizing bacteria, enhancing coupling partial nitritation and anammox. These findings help further our understanding of the mechanisms of anammox biofilm nitrogen removal and provide a baseline for optimization of the design of carrier structures.
This study developed an innovative process for the treatment of low-ammonium wastewater in a single-stage bioreactor over 250 days. Partial nitritation-anammox and partial denitritation-anammox ...(PN/A-PDN/A) processes were combined under aerobic/anoxic operation, and a high nitrogen removal efficiency (94.6%) was obtained at a nitrogen removal rate of 0.54 kg N m–3 d–1 and a chemical oxygen demand to total inorganic nitrogen (COD/TIN) ratio of 0.28. Mass balance analysis identified anammox as the dominant nitrogen removal pathway, achieving 88.3% nitrogen loss. The abundance of anammox bacteria and their bioactivity rapidly increased and were effectively maintained, as indicated by qPCR and bioactivity tests. The PN/A-PDN/A process provided two pathways of nitrite production for anammox, which favored the enrichment of anammox bacteria and stable processing. In addition, the enrichment of anammox bacteria was promoted by selective floc discharge since anammox bacteria are mainly located in granules (relative abundance of 29.64 ± 7.89%). Competitive organisms (including heterotrophic bacteria and nitrite oxidizing bacteria), enriched in flocs, were washed out. Overall, these findings confirmed anammox, sequentially combined with PN and PDN via aerobic/anoxic strategy, as a promising alternative for mainstream anammox.
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•Activated sludge reduction was obviously improved by adding nitrite of 0.2 g/gVSS.•Nitrite addition enhanced the disintegration of protein, especially in TB-EPS.•Nitrite lead to the ...decrease of microbial diversity, causing cell death and lysis.•Sludge reduction was associated with both TB-EPS degradation and cell lysis.
Extracellular nitrite has been used to improve the digestion of waste activated sludge (WAS). However, the underlying mechanism remains largely unknown. In this study, WAS was treated with 0.2 gNO2−-N/gVSS for 7 days and its performance was compared to that of aerobic and anaerobic treatments. The addition of nitrite had a distinct effect on the reduction of VSS/SS and the accumulation of soluble organics compared to the control reactors. As evident by the variations of extracellular polymeric substances (EPS), nitrite addition had a positive effect on decreasing protein. In particular, the decrease of protein mainly occurred in tightly bound EPS (TB-EPS), which caused sludge disintegration and enhanced sludge reduction. Additionally, the decrease of microbial diversity with nitrite addition was significant compared to the control reactors, accompany with a decrease of live/dead cells ratio and an increase of supernatant DNA concentration. This suggests that nitrite could cause cell death and lysis, resulting in sludge degradation. Thus, nitrite addition enhanced sludge treatment through the combined effect of TB-EPS disintegration and cell lysis. These findings will be useful for the optimization of sludge treatment process based on nitrite addition.
The successful implementation of Vessel Traffic Services (VTS) relies heavily on human decisions. With the increasing development of maritime traffic, there is an urgent need to provide a sound ...support for dynamic risk appraisals and decision support. This research introduces a cellular automata (CA) simulation-based modelling approach the objective of which is to analyze and evaluate real-time maritime traffic risks in port environments. The first component is the design of a CA model to monitor ships’ behavior and maritime fairway traffic. The second component is the refinement of the modelling approach by combining a cloud model with expert knowledge. The third component establishes a risk assessment model based on a fuzzy comprehensive evaluation. A typical scenario was experimentally implemented to validate the model’s efficiency and operationality.
This study investigates the sampled-data admissibility problem for a singular system. The objective of this paper is to design a sampled-data controller to ensure the admissibility of a singular ...system and to construct an appropriate Lyapunov–Krasovskii functional (LKF) to get less conservative results for the sampled-data singular system. To accomplish these objectives, the system is converted into a time-delay system by the input delay approach firstly, and both lower and upper bounds of the delay are considered. Secondly, by introducing a suitable LKF, the admissibility criteria are obtained. Then, when estimating the derivative of the LKF, a relaxation variable is introduced by the method of reciprocally convex inequality, and it is proved that the conservatism is reduced. Finally, two numerical examples are given to prove that the designed sampled-data controller can ensure the states of the systems under the influence of external interference.
This paper investigates the aperiodic sampled-data control for a chaotic system. Firstly, Takagi–Sugeno (T-S) fuzzy models for the chaotic systems are established. The lower and upper bounds of the ...sampling period are taken into consideration. Then, the criteria for mean square exponential stability analysis and aperiodic sampled-data controller synthesis are provided by means of linear matrix inequalities. And the real sampling patterns can be fully captured by constructing suitable Lyapunov functions. Finally, an illustrative example shows that the proposed method is effective to guarantee that the system’s states are stable with aperiodic sampled data.
Existing research on auto-berthing of ships has mainly focused on the design and implementation of controllers for automatic berthing. For the real automatic docking processes, not only do external ...environmental perturbations need to be taken into account but also motion paths, docking strategies and ship mechanical constraints, which are important influential factors to measure autonomous docking methods. Through a literature review of ship path planning and motion control for automatic berthing, it is found that many studies ignore the interference of the actual navigational environment, especially for ships sailing at slow speed when berthing, or do not consider the physical constraints of the steering gear and the main engine. In this paper, we propose a hybrid approach for autonomous berthing control systems based on a Linear Quadratic Regulator (LQR) and Covariance Matrix Adaptation Evolution Strategy (CMA-ES), which systematically addresses the problems involved in the berthing process, such as path planning, optimal control, adaptive berthing strategies, dynamic environmental perturbations and physically enforced structural constraints. The berthing control system based on the LQR and modified LQR-CMA-ES have been validated by simulation work. The simulation results show that the proposed method is able to achieve the automatic docking of the ship well and the system is robust and well adapted to environmental disturbances at slow speed when docking.
This study addresses the sliding mode control (SMC) issue for time-delay Markovian jump singular systems. Firstly, the T-S fuzzy mode is established for the system. Secondly, novel integral-type ...fuzzy sliding surfaces are constructed for accommodating the system’s model characteristics. Thirdly, free-weighting matrix technique combined with Lyapunov-Krasovskii functional are used for guaranteeing the admissibility and passivity of the system. Finally, the effectiveness of the proposed approach is verified by simulation result.
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