Path Following of Underactuated Autonomous Surface Vessels With Surge Velocity Constraint and Asymmetric Saturation

Dear Editor, This letter is concerned with the path following of underactuated autonomous surface vessels(ASV) in the presence of surge velocity constraint and asymmetric saturation as well as unknown dynamics.To cope with velocity constraints both magnitude and rate and asymmetric saturation as well as unknown dynamics, an adaptive finitetime sliding mode control scheme(AFTSM) is designed.

Research on the navigational risk of liquefied natural gas carriers in an inland river based on entropy:A cloud evaluation model

Due to the flammability and explosive nature of liquefied natural gas(LNG),an extremely strict process is followed for the transporta-tion of LNG carriers in China.Particularly,no LNG carriers are operating in inland rivers within the country.Therefore,to ensure the future navigation safety of LNG carriers entering the Yangtze River,the risk sources of LNG carriers’navigation safety must be identi-fied and evaluated.Based on the Delphi and expert experience method,this paper analyses and discusses the navigation risk factors of LNG carriers in the lower reaches of the Yangtze River from four aspects(human,ship,environment and management),identifies 12 risk indicators affecting the navigation of LNG carriers and establishes a risk evaluation index system.Further,an entropy weight fuzzy model is utilized to reduce the influence of subjective judgement on the index weight as well as to conduct a segmented and overall evaluation of LNG navigation risks in the Baimaosha Channel.Finally,the cloud model is applied to validate the consistent feasibility of the entropy weight fuzzy model.The research results indicate that the method provides effective technical support for further study on the navigation security of LNG carriers in inland rivers.

DNS in evolution of vorticity and sign relationship in wake transition of a circular cylinder:(pure)mode A

In the present paper,the spatio-temporal evolution of vorticity in the first wake instability,i.e.,(pure)mode A,is investigated in order to understand the wake vortex dynamics and sign relationships among vorticity components.Direct numerical simulation(DNS)for the flow past a circular cylinder is performed,typically at a Reynolds number of 200,in the three-dimensional(3-D)wake transition.According to characteristics of time histories of fluid forces,three different stages are identified as the computational transition,the initial stage and fully developed wake.In the second initial stage,the original two-dimensional spanwise vortices become obviously three-dimensional associated with the streamwise or vertical vorticity intensified up to about 0.1.As a matter of fact,these additional vorticities,caused by the intrinsic 3-D instability,are already generated firstly on cylinder surfaces early in the computational transition,indicating that the three-dimensionality appeared early near the cylinder.The evolution of additional components of vorticity with features the same as mode A shows that(pure)mode A can be already formed in the late computational transition.Through careful analysis of the vorticity field on the front surface,in the shear layers and near wake at typical times,two sign laws are obtained.They illustrate intrinsic relationships among three vorticity components,irrelevant to the wavelength or Fourier mode and Reynolds number in(pure)mode A.Most importantly,the origin of streamwise vortices is found and explained by a new physical mechanism based on the theory of vortex-induced vortex.As a result,the whole process of formation and shedding vortices with these vorticities is firstly and completely illustrated.Other characteristics are presented in detail.

Design and Simulation of Single Hull Side Structure Based on Filling Sandwich

Ship collision accidents are catastrophic accidents, and as the main energy-absorbing structure, the anti-collision capacity of the side structure has an important influence on the crashworthiness of the ship. It is necessary to improve the crashworthiness of the ship by increasing energy absorption of the side structure, in such ways as adding a filling sandwich in a single hull. The aim of the present study is to discuss the crashworthiness of the side structure stressed under lateral dynamic loads through simulation with the finite element code MSC/Dytran. The collision force, the damage deformation, the critical collision speed as well as the energy absorption of a side structure improved with a filling sandwich are compared to the standard structure through numerical simulations. The results indicate that a sandwich panel structure is an advanced ship protection structure that can remarkably improve the ability of the side structure to withstand collisions; the effect of the tube-style sandwich panel structure has the best results. The outcome of this study provides a reference for the crashworthiness assessment of side structures and the crashworthiness optimization design of new side structures.

Synthesis and Characterization of CePO_4 Nanorods via Solvothermal Process

One-dimensional cerium phosphate(CePO4) nanorods were successfully synthesized by a facile and simple solvothermal method at 150 ℃ for 12 h, using Ce(NO3)3·6H2O and NaH2PO4·2H2O as the starting materials. Phase and morphologie of the as-synthesized CePO4 products, characterized by XRD, FESEM, and TEM, were proved to be perfect and uniform hexagonal CePO4 nanorods with aspect ratio of more than 100. The photoluminescence(PL) spectrometer was used to investigate the optical properties of the assynthesized hexagonal CePO4 nanorods.

Syntheses, Structures and Properties of Two Mn(Ⅱ) Clusters Based on 1,10-Phenanthroline-2,9-dicarbaldehyde Dioxime Ligand

Two novel clusters [MnⅢ3（μ3-O）（phendox）3]X·13H2O(X = Cl（1）, Br（2]） have been obtained from the solvothermal reactions of 1,10-phenanthroline-2,9-dicarbaldehyde dioxime（H2phendox） with MnCl2·4H2O or anhydrous MnBr2, and their structures were characterized by elemental analysis, FT-IR, XRD, TGA, MS and single-crystal X-ray diffraction. It crystallizes in trigonal, space group P31/c. X-ray analysis reveals that the neighbouring [Mn3（μ3-O）（phendox）3]+ cores are linked by C–H···Cl hydrogen bonds and form an infinite supramolecular chain along the c-axis. Neighbouring chains are packed with each other by off-set p-p interactions of the aromatic rings on phenox2-. A 3D supramolecular architecture in a honeycomb topology is formed with 1D hexagonal channel in the dimensions of 13? × 13? along the c-axis. The gas adsorption studies show that compound 1·13H2O is stable upon the removal of guest molecules and the desolvated compound absorbed considerable amount of CO2.

Vulnerability assessment of crop production to climate change across Northwest China during 1995–2014

Crop production vulnerability to climate change in Northwest China depends upon multiple socio-ecological factors.Knowledge regarding the specific indicators and methods suitable for assessing crop production vulnerability is limited that address spatiotemporal variations across large and diverse zones.We propose an integrated assessment framework to quantify the vulnerability of crop production derived from crop yield sensitivity,exposure,and adaptive consequences across 338 counties in Northwest China during 1995–2014.Maps on these indices were generated using climatic and socioeconomic data with spatial mapping method.Different clusters of crop production vulnerability were then identified by a k-means cluster method to assess the heterogeneity of vulnerability at a regional scale.Results show that the vulnerability of crop production in 338 counties varies significantly in both geographical and socioeconomic aspects,specifically,vulnerability indicators are generally higher in Minhe,Menyuan,Hualong,and Ledu,and Xayar had the lowest value of vulnerability.This indicates that adaptation strategies for regional crop production need to focus on several levels,from the improvement of adaptive ability to crop yield fluctuation by promoting irrigation agriculture and optimizing limited water resources in typical arid areas,to agriculture-related financial policies incentivizing the capital investment and technology upgrade of crop production on traditional farming regions.This study provides convincing evidence that the factors related to socioeconomic policies are particularly alarming when a crop’s risk is compared to precipitation fluctuations.We recommend these findings be used to facilitate regional agriculture planning to reduce crop production vulnerability and ensure sustainable food security in specific regions.

Application of Risk Index to Risk-Based Decision-Making in Vessel Traffic Service System

The applications of risk index to risk estimation, risk acceptability, and cost-benefit analysis for planning vessel traffic service (VTS) system were analyzed. An example of Wuhan Port shows that its application is easily implemented and can be helpful in a comprehensive and scientific decision-making. Especially aiming to the difficult problems with respect to risk prediction, risk acceptability and cost-benefit assessment, this article put forward some new solutions based on risk-index, such as the trendline estimation, ALARP (as low as reasonably practicable) matrix and weighted cost-benefit analysis, with a fairly good operability and comparability.

Assessment and Countermeasures for Offshore Wind Farm Risks Based on a Dynamic Bayesian Network

Wind power is a kind of clean energy promising significant social and environmental benefits, and in The Peoples Republic of China, the government supports and encourages the development of wind power as one element in a shift to renewable energy. In recent years however, maritime safety issues have arisen during offshore wind power construction and attendant production processes associated with the rapid promotion and development of offshore wind farms. Therefore, it is necessary to carry out risk assessment for phases in the life cycle of offshore wind farms. This paper reports on a risk assessment model based on a Dynamic Bayesian network that performs offshore wind farms maritime risk assessment. The advantage of this approach is the way in which a Bayesian model expresses uncertainty. Furthermore, such models permit simulations and reenactment of accidents in a virtual environment. There were several goals in this research. Offshore wind power project risk identification and evaluation theories and methods were explored to identify the sources of risk during different phases of the offshore wind farm life cycle. Based on this foundation, a dynamic Bayesian network model with Genie was established, and evaluated, in terms of its effectiveness for analysis of risk during different phases of the offshore wind farm life cycle. Research results show that a dynamic Bayesian network method can perform risk assessments effectively and flexibly, responding to the actual context of offshore wind power construction. Historical data and almost real-time information are combined to analyze the risk of the construction of offshore wind power. Our results inform a discussion of security and risk mitigation measures that when implemented, could improve safety. This work has value as a reference and guide for the safe development of offshore wind power.

Research on Anti-collision Capability and Safety Supervision Measures of the Nanjing Yangtze River Bridge

With the vigorous development of inland river shipping economy,the trend of large ships passing Nanjing Yangtze River Bridge is obvious.The standard formula of ship collision force is selected by comparing the empirical calculation formulas.Four representative ship types are selected for calculation and analyzing of collision force.It is concluded that the anti-collision ability of the Nanjing Yangtze River Bridge does not meet the requirement of large ship collision force when the speed is more than 8-knots.From the perspective of active collision avoidance,this paper puts forward the navigation safety supervision countermeasures.A conceptual model of guided pulley anti-collision device is designed from the perspective of passive anti-collision.The research results provide references for safety supervision and anti-collision measures for the bridge.

Evaluation Method for Tunneling Stability of TBM Cutterhead

In the process of tunneling of tunnel boring machine (TBM), different geological conditions often correspond to different working conditions, and the randomness of geological conditions also causes the order of occurrence of each working condition to be different. Under the conversion of different working conditions, this makes the vibration of different types of cutterheads different. How to choose the appropriate type of cutterhead according to different geological conditions is very important for saving engineering cost and increasing cutterhead life. In view of the above situation, this paper proposes a stability evaluation method during the TBM tunneling process to select the appropriate cutterhead type. Firstly, the corresponding relationship between geology and working conditions is established according to different geological conditions, and the input loads corresponding to geological conditions are obtained. Then, it is substituted into the dynamic model of the cutterhead system, the vibration response boundaries of each degree of freedom are obtained by solving. And the average value of the maximum boundary amplitude of each degree of freedom is taken to represent the extreme vibration of the cutterhead under the corresponding working conditions. Finally, by comparing the fluctuation of the ultimate vibration amplitude of each type of cutterhead in the process of working condition conversion, the results are as follows: when the transition between homogeneous strata and composite strata is normal and there is no large turning and deviation correction, the vibration response of the two-part cutterhead is the smallest, and the two-part cutterhead is the best choice. Otherwise, the five-part cutterhead is the best choice, while the stability of the integrated cutterhead is the worst.

Neutrosophic Adaptive Clustering Optimization in Genetic Algorithm and Its Application in Cubic Assignment Problem

In optimization theory,the adaptive control of the optimization process is an important goal that people pursue.To solve this problem,this study introduces the idea of neutrosophic decision-making into classical heuristic algorithm,and proposes a novel neutrosophic adaptive clustering optimization thought,which is applied in a novel neutrosophic genetic algorithm(NGA),for example.The main feature of NGA is that the NGA treats the crossover effect as a neutrosophic fuzzy set,the variation ratio as a structural parameter,the crossover effect as a benefit parameter and the variation effect as a cost parameter,and then a neutrosophic fitness function value is created.Finally,a high order assignment problem in warehousemanagement is taken to illustrate the effectiveness of NGA.

A new interpolation method based on satellite physical character in using IGS precise ephemeris

Due to the deficiency of sliding Lagrange polynomial interpolation,the author proposes a new interpolation method,which considers the physical character of satellite movement in coordinate transformation and reasonable selection of interpolation function.Precision of the two methods is compared by a numerical example.The result shows that the new method is superior to the sliding Lagrange polynomial interpolation in interpolation and extrapolation,especially in extrapolation that is over short time spans.

护卫舰横摇稳定舵的H∞/H2控制器的设计和比较（英文）

Roll motion of ships can be distinguished in two parts:an unavoidable part due to their natural movement while turning and an unwanted and avoidable part that is due to encounter with waves and rough seas in general.For the attenuation of the unwanted part of roll motion,ways have been developed such as addition of controllable fins and changes in shape.This paper investigates the effectiveness of augmenting the rudder used for rejecting part of the unwanted roll,while maintaining steering and course changing ability.For this purpose,a controller is designed,which acts through intentional superposition of fast,compared with course change,movements of rudder,in order to attenuate the high-frequency roll effects from encountering rough seas.The results obtained by simulation to exogenous disturbance support the conclusion that the roll stabilization for displacement can be effective at least when displacement hull vessels are considered.Moreover,robust stability and performance is verified for the proposed control scheme over the entire operating range of interest.

Simulation Research on Operation of Union Purchase System in Navigation Simulator

Navigation is the only way to develop and utilize marine resources,while the promotion of seafarers1 quality is the basic force of navigation,so navigation simulator plays an important role in modern navigation education.The simulation research on the operation of the union purchase is important to improve the special operation training of the actual cargo handling of the union purchase.On the basis of the Cartesian coordinate system transformation algorithm,the algorithm model of the union purchase operation is constructed.On the basis of three-dimensional(3D)rendering engine technology of open scene graph(OSG),the algorithm model of finding the space coordinates of the cargo point is established.The model of catenary equation is used to optimize the scene appearance of the cargo wire.By combination of QT channel signal mechanism and OSG,the simulation interaction of the union purchase operating system is realized.By acquiring the 3D coordinate values of each point,we fit the trajectories of each point in the operation and compare the trajectories.The results show that the model has high interactivity and small error.The comparison of the states of the cargo wire before and after optimization shows that the optimized wire is more realistic and the high fidelity meets the needs of operational training and simulation systems.

三体船构型水动力性能试验研究

This paper presents experimental results on configuration hydrodynamics.Three models are used in the model tests,which are typical of hard,round,and soft chines.Although specific values are different,the influence patterns are similar in the three ship models.A set of different outrigger positions is investigated in calm water and regular waves.A variety of interesting phenomena are observed,among which the splash resistance is the dominant component for a trimaran at high speeds(with Froude number Fr>0.6).If two small outriggers are placed inside Kelvin’s wave systems of the main hull,a strong splash appears,resulting in a significant resistance increase.Moreover,short and long waves cannot be neglected,for they may excite the motions of much smaller outriggers.This condition leads to non-vanishing heaving at high-frequency and non-normalized pitches at low frequencies.Based on the tests,three spectra of optimum configurations for resistance,longitudinal motions,and transverse motions are presented.These results reveal the optimum configurations of a trimaran hull in terms of hydrodynamic performance,thus providing a very powerful tool for optimum design of trimaran ships.

Remote Sensing Monitoring Method Based on BDS-Based Maritime Joint Positioning Model

Complicated sea conditions have a serious impact on ship navigation safety and even maritime accidents.Accordingly,this paper proposes a remote sensing monitoring method based on the Beidou Navigation Satellite System(BDS)maritime joint positioning model.This method is mainly based on the BDS and multiple Global Navigation Satellite Systems(GNSS)to build a data fusion model,which can capture more steady positioning,navigation,and timing(PNT)data.Compared with the current Global Positioning System(GPS)and Global Navigation Satellite System(GLONASS)mandatory used by the International Maritime Organization(IMO),this model has the characteristics of more accurate positioning data and stronger stability.The static and dynamic measurement show that such a model works for maritime ships and maritime engineering.Combined with the Ship’s Automatic Identification System(AIS)and Geographic Information System(GIS),a BDS-based remote sensing monitoring method can cover the world,serve maritime ships and construct maritime engineering.

Hydraulic Characteristics of Multi-Stage Orifice Plate

Energy dissipater of multi-stage orifice plate, as a kind of effective energy dissipater with characteristics of high energy dissipation ratio and low cavitations risk, has become welcomed more and more by hydraulics researchers. The relationship between the contraction ratio of upper stage orifice plate and the lower one's under the principle of equal-cavitation characteristics, and the reasonable distance between upper stage orifice plate and the lower one under the condition of complying with this principle, are two important factors to be considered for multi-stage energy dissipater design. In the present paper, these two factors were analyzed by theoretical consideration and numerical simulations, and solving methods were put forward. The conclusion in this paper was proved to be reasonable by model experiment.

Safety Limitations of Large New-Built Seagoing Vessels Towed through Bridge Area

The safety limitation of large new-built seagoing vessel design and operation is investigated to ensure safety of the new vessels towed through bridge area. We analyze the maneuverability characteristics of a towing fleet, and develop a mathematical drift model of ship motion for the fleet. Based on this drift model and the hydro-meteorological conditions in bridge area, we propose a method to systematically ascertain the safety limitations of water stages, current, wind, speed and visibility. This method is conducive to the safety of both navigation and bridges when large towing fleets transit through bridges.

Estimation of buoy drifting based on adaptive parameter-varying time scale Kalman filter

To solve Kalman filter with dynamic time scale problem,an adaptive parameter-varying time scale kalman filter(APVTS-KF)is designed.An adaptive mechanism for choosing the covariance of state noise is designed.APVTS-KF is used to estimate the buoy drifting trajectory with different report intervals.Position drifting data of four buoys are used to test the proposed algorithm.The influence of report interval,drifting distance,adaptive factor and noise covariance are analysed and compared.The experimental results and error analysis show that APVTS-KF is better than other algorithms in trajectory estimation.Thus,Kalman filtering can be used for accurate trajectory estimation in the actual situation of buoy drifting with dynamic time intervals.