水下潜器改进S面控制及控制系统仿真

S surface controllers have been proven to provide effective motion control for an autonomous underwater vehicle (AUV). However, it is difficult to adjust their control parameters manually. Choosing the optimum parameters for the controller of a particular AUV is a significant challenge. To automate the process, a modified particle swarm optimization (MPSO) algorithm was proposed. It was based on immune theory, and used a nonlinear regression strategy for inertia weight to optimize AUV control parameters. A semi-physical simulation system for the AUV was developed as a platform to verify the proposed control method, and its structure was considered. The simulation results indicated that the semi-physical simulation platform was helpful, the optimization algorithm has good local and global searching abilities, and the method can be reliably used for an AUV.     

FLUXMANCHE radiotracers measurements: A contribution to the dynamics of the English Channel and North Sea

From 1986 to 1992, ¹²⁵Sb released by the nuclear fuel reprocessing plant at La Hague has been used to study the transfer of waters from mid-Channel areas towards the Straits of Dover. Since 1940, these investigations have formed part of the MAST 53 FLUXMANCHE programme and have involved repeated measurements on a Straits of Dover transect. A discussion of the results is presented here which takes into account new information provided by a hydrodynamic model developed in the framework of FLUXMANCHE; it combines knowledge of the monthly fluxes of water trough the Straits of Dover and week-by-week simulation of the ¹²⁵Sb activities of waters flowing in this aera. It is proposed that soluble radionuclides introduced into the central Channel are transferred towards the Straits of Dover over a time which varies from four to seven months depending on the route taken.     

Multiple USV cooperative algorithm method for hunting intelligent escaped targets北大核心CSCD

[目的]针对无人艇协同围捕过程中逃跑目标具备智能性,现有无人艇策略难以围捕成功的问题,提出一种基于双层切换策略的多无人艇协同围捕算法。[方法]第1层围捕策略采用改进势点法,以无人艇与势点的总直线距离最小为优化目标,采用匈牙利算法为无人艇动态分配势点,并采用人工势场法实现无人艇的协同避碰;第2层围捕策略利用了阿波罗尼奥斯圆的性质,在两艘无人艇前往逃跑目标的目标点进行拦截,剩余无人艇运动方向保持与逃跑目标相同,以不断缩紧包围区域;为应对逃跑目标不同的逃跑方式,第1层围捕策略和第2层围捕策略可互相转化。[结果]仿真实验表明,该算法相较于顺序分配势点算法和极角分配势点算法,围捕时间更少或持平,证明了该算法的有效性和先进性。[结论]该多无人艇协同双层围捕算法,对具备典型智能性的逃跑目标具有围捕效果。     

层间水对水下双层结构撞击历程的影响分析

双层壳体结构是潜艇等大型水下结构的重要结构形式,潜艇结构的水下碰撞是潜艇的主要事故形式,然而,针对双层壳体的潜艇结构水下碰撞问题的研究工作目前却极为有限.文中首先提出潜艇碰撞问题,并对其碰撞特征进行分析,然后针对潜艇水下碰撞环境下,层间水对碰撞历程的影响和双层结构的碰撞特点进行了理论分析,在数值仿真计算的基础上,着重讨论了双层板结构在碰撞过程中,层间水对撞击速度、碰撞力以及双层板吸能特性的影响,分析结果显示,层间水对双层壳板撞击历程的影响主要体现在两方面:一是接触初始阶段,耐压壳板将由于层间水的存在,与非耐压壳板组成抗冲击弹簧体系参与抗冲击作用,吸收冲击能量,这对于双层壳板的防撞性能是有利的;二是非耐压壳板穿透后,层间水的影响主要体现为水对耐压壳板的粘附作用,耐压壳板的抗撞能力显著下降.     

Assessment of sea surface temperature observational networks in the Baltic Sea and North Sea

The satellite and in situ Sea Surface Temperature (SST) observational networks in the Baltic Sea and North Sea are evaluated based on the quality of the gridded SST products generated from the networks. A multi-indicator approach is applied in the assessment. It includes evaluation of data quality, effective data coverage, field reconstruction error and model nowcast error. The results show that the best available full-coverage SST product is generated by assimilating the SST observations to obtain a yearly mean model bias of 0.07 °C and RMSE of 0.64 °C. The effective data coverage rate is 31% by using AVHRR (Advanced Very High Resolution Radiometer) data from NOAA (National Ocean and Atmosphere Administration) satellites 12, 14 and 16. The data redundancy increases rapidly with the number of infrared sensors. Using either NOAA satellite 12 or all 3 satellites makes a small difference with regard to derived effective coverage and the ocean model nowcast error. The influence of using the in situ SST observations in the SST field reconstruction is negligibly small. Instead, the major role of in situ SST observations is in calibrating the satellite observations. To study the relative importance of data quality and data coverage, an assessment is done for two satellite products: one product is based entirely on NOAA 12 data and has larger coverage but lower quality. The other product is a subset of the SAF products (derived from NOAA 14 and 16) and has lower coverage but higher quality. Based on current monitoring, modelling and assimilation technology, the results suggest that the data quality is an important factor in further improving the quality of the gridded SST products. Recommendations are made for possible further improvements of the existing SST observational networks.     

粉尘爆炸及“杂混合物”对其特性的影响

在工业粉体加工、装卸、储运和处理的过程中,时有爆炸火灾的发生,因粉体静电,尤其是含不份较低的碳氢化合物粉体及绝缘性高的高分子化合物粉粒的静电引起的爆炸占有一定的比例。作者首先论述粉尘爆炸的特点及机理,接着论述“杂混合物”对粉尘爆炸特性的影响：介绍粉尘的爆炸特性,以试验数据描述“杂混合物”对爆炸极限、爆炸压力－强度的影响以及“杂混合物”中可燃气含量及其最低最小点火能量的关系。最后剖析ＬＤＰＥ粉粒在贮     

An overview of the abundance and role of protozooplankton in Antarctic waters

The classic view of the Antarctic pelagic system has suggested that food web dynamics are dominated by the diatom-krill food web link. Recent observations, however, have indicated that this is an oversimplification and that the antarctic food web has a complexity similar to that found in lower latitude systems. More specifically, small particulate feeding protozoans appear to have a much greater importance than was previously assumed.Only a few studies have been sufficiently extensive to characterize the Antarctic pelagic protozoan assemblage. These indicate that heterotrophic flagellates (dinoflagellates and other heterotrophic nanoplankton) and ciliates (mostly non-loricate oligotrichs) dominate the protozooplankton assemblages in surface waters. The combined biomass of protozooplankton has been reported to comprise from < 7 to > 75% of the total nano- and microplankton biomass depending on season and location. Protozoans are also found in sea ice communities where their abundances exceed those typically found in the plankton. Several protozoan species occupy both ice and water habitats, suggesting that seasonally melting sea ice may be the source of ice-edge protozooplankton assemblages.The feeding rates of protozooplankton in Antarctic waters are poorly documented. Consumption estimates based on clearance rates and some preliminary grazing experiments, however, indicate that the protozooplankton should be capable of utilizing a significant proportion of the daily primary and bacterioplankton production. Protozoans may contribute to vertical flux, but present evidence suggests that their contribution will be lower than from other sources.     

舰船装备健康状态评估及其应用研究

文章分析了装备健康状态评估的国内外研究现状,对装备健康状态及其与技术状态之间的关系进行了较为深入的探讨,明确了舰船装备健康状态与技术状态之间的区别和联系,以及利用健康状态和技术状态进行装备状态评估的优缺点。最后根据舰船装备的实际需求,将舰船健康状态的概念引入到舰船的使用和维修过程中,提出了健康状态在舰船使用、维修和训练方面的应用设想。     

Fuzzy sliding mode control method for vertical motion of autonomous underwater gliders北大核心CSCD

［Objective］This paper proposes a fuzzy sliding mode controller based on T-S fuzzy logic for the vertical plane motion control of an autonomous underwater glider (AUG) with limited actuator capability. ［Methods］In the fuzzy sliding mode controller, the fuzzy switching rate is used to replace the switching rate in the fixed time controller to effectively suppress buffeting. The fuzzy switching rate is obtained by fitting the switching rate of the fixed time controller with T-S fuzzy rules. Based on the limited capabilities of AUG actuators, a saturation auxiliary system is designed to improve the actuator saturation effect. Finally, the performance of the system is verified by Lyapunov stability analysis and numerical simulation. ［Results］The results show that the AUG under the fuzzy sliding mode controller and the saturation auxiliary system can converge in finite time. The effectiveness of the fuzzy sliding mode controller and the saturation auxiliary system are verified by numerical simulation. ［Conclusions］By making comparisons with the fixed-time controller, it is verified that the two controllers have similar control performance, and the buffeting of the fuzzy sliding mode controller is lesser. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Influence of slip boundary on flow separation and drag of flow past bluff body at high Reynolds numbers北大核心CSCD

［Objectives］Flow separation increases the drag and noise of underwater vehicles, and influences the controllability of their control surfaces. Therefore, the influence of slip caused by superhydrophobic surfaces on drag reduction and flow separation is studied. ［Methods］A partial slip boundary condition is developed, and the flow around a circular cylinder and foil with a slip boundary at high Reynolds numbers are numerically simulated. ［Results］The results show that the when the slip length increases, the flow around the cylinder goes through three stages: the turbulent Kármán vortex street, laminar Kármán vortex street and non-separation Stokes flow. The drag coefficient increases first and then decreases, and the vortex shedding frequency increases. For flow around a foil, the separation position moves downstream until the separation region disappears when the slip length increases, and the drag coefficient decreases while the lift coefficient increases. ［Conclusions］The results of this study show that for flow past bluff body at high Reynolds number, the slip boundary can control flow separation and reduce drag effectively, providing technical support for the application of superhydrophobic surfaces for the flow control of underwater vehicle appendages. © 2022 Journal of Clinical Hepatology. All rights reserved.