The statistical observation localized equivalent-weights particle filter in a simple nonlinear model     

Yuxin Zhao  Shuo Yang  Renfeng Jia  Di Zhou  Xiong Deng  Chang Liu  Xinrong Wu 《海洋学报(英文版)》2022,41(2):80-90

This paper presents an improved approach based on the equivalent-weights particle filter(EWPF) that uses the proposal density to effectively improve the traditional particle filter. The proposed approach uses historical data to calculate statistical observations instead of the future observations used in the EWPF’s proposal density and draws on the localization scheme used in the localized PF(LPF) to construct the localized EWPF. The new approach is called the statistical observation localized E...  相似文献   

一类三次超越多项式零点的分布及其在时滞生物系统的应用     

阮士贵  魏俊杰  肖冬梅 《南京气象学院学报》2017,9(4):381-390

本文讨论了一类三次超越多项式零点的分布,给出了零点分布在左半复平面、穿过虚轴和进入右半复平面的充分条件.作为应用,考虑了带时滞的三种群食物链模型、带时滞的睾酮分泌模型、带时滞的HIV体内感染动力学模型、带时滞的葡萄糖-胰岛素模型、带时滞的肿瘤-免疫系统作用模型的稳定性和分支问题.  相似文献   

Evaluation of groundwater potential and eco-geological environment quality in Sanjiang Plain of Heilongjiang Province          下载免费PDF全文

WU Ting-wen  WANG Li-huan  YANG Xiang-kui 《地下水科学与工程》2017,5(2):193-201

Sanjiang Plain of Heilongjiang Province has become an important commodity grain base in our country after the construction of more than a century. Groundwater is the main water source for industrial and agricultural production and daily life in the area. With the large-scale development and construction in this area, there are a series of ecological and environmental geological problems, such as the reduction of groundwater resources, which seriously restricts the sustainable development of local agriculture and society as well as economy. Based on the characteristics of three-dimensional flowof groundwater in Sanjiang Plain, this paper adopts the simulation software Visual MODFLOW to evaluate groundwater exploitation potential. The results show that overall there is a certain exploitation potential of Sanjiang Plain groundwater but it is unevenly distributed, and overdraft phenomenon exists in seven farms such as Baoquanling and Chuangye. Based on analytic hierarchy process, the evaluation result of eco-geological environment quality in Sanjiang Plain shows that 94.5% of the region features good geological environment quality, medium stability and medium bearing capacity. The study can provide geological evidence for optimal allocation of water resources, land planning and regulation, and the high and stable yield of the commodity grain base in Sanjiang Plain.  相似文献   

船舶在平整冰区行进过程的离散元分析          下载免费PDF全文

狄少丞  季顺迎  薛彦卓 《海洋工程》2017,35(3):59-69

船舶在冰区航行中,冰荷载是船舶结构设计和安全航行的重要影响因素。采用具有黏结破碎特征的离散单元法对船舶在平整冰区的航行过程进行了数值分析。在船舶破冰过程的离散元模拟中,平整冰由球形颗粒黏结而成,同时考虑了海水浮力和拖曳力对海冰单元的作用,颗粒间的黏结作用可在海冰与船体的相互作用过程中发生破碎;船体由三角形单元构造,分析了在海水浮力、推进器推力及海冰共同作用下船体的六自由度运动特性。通过船体与海冰相互作用的离散元分析,确定了船舶在破冰过程中海冰作用在船体上的冰荷载,探讨了船舶推进器推力和海冰厚度对冰荷载的影响,并与Lindqvist船体冰阻力经验公式进行了对比。  相似文献   

Quadratic Dissipation Effect on the Moonpool Resonance     

LIU Heng-xu  CHEN Hai-long  ZHANG Liang  ZHANG Wan-chao  LIU Ming 《海洋工程》2017,(6):665-673

This paper adopted a semi-analytical method based on eigenfunction matching to solve the problem of sharp resonance of cylindrical structures with a moonpool that has a restricted entrance. To eliminate the sharp resonance and to measure the viscous effect, a quadratic dissipation is introduced by assuming an additional dissipative disk at the moonpool entrance. The fluid domain is divided into five cylindrical subdomains, and the velocity potential in each subdomain is obtained by meeting the Laplace equation as well as the boundary conditions. The free-surface elevation at the center of the moonpool, along with the pressure and velocity at the restricted entrance for first-order wave are evaluated. By choosing appropriate dissipation coefficients, the free-surface elevation calculated at the center of the moonpool is in coincidence with the measurements in model tests both at the peak period and amplitude at resonance. It is shown that the sharp resonance in the potential flow theory can be eliminated and the viscous effect can be estimated with a simple method in some provided hydrodynamic models.  相似文献   

Remote sensing of surface currents with single shipborne high-frequency surface wave radar     

Zhongbao Wang  Junhao Xie  Zhenyuan Ji  Taifan Quan 《Ocean Dynamics》2016,66(1):27-39

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随钻声波测井FDTD模拟及钻铤波传播特性研究   总被引：5，自引：4，他引：1       下载免费PDF全文

杨玉峰  关威  崔乃刚  胡恒山  郑晓波 《地球物理学报》2016,59(1):368-380

幅度大的钻铤波掩盖地层信号是困扰随钻声波测井技术的难题,认识钻铤波特性对于消除或有效降低钻铤波至关重要.记录岩石动电效应引起电磁场的随钻动电测井,被认为有望彻底解决钻铤波干扰问题.本文采用有限差分法,模拟不同钻铤、不同井孔结构的随钻声场,对比分析了单极源钻铤波的传播特性,阐明存在伴随钻铤波动电信号的原因.结果表明:钻铤声波在沿钻铤传播时向外部介质辐射能量,透过井壁进入地层的具有视钻铤波速度的声波,与地层纵横波一样可发生动电转化,因而可导致随钻动电测井时产生钻铤波速度的电磁信号.计算还表明,高频情况下,随钻声波测井钻铤波呈现两阶模式:具有低频截止频率的高阶钻铤波幅度较小,其速度略低于钻铤纵波速度;无截止频率的低阶钻铤波幅度较大,其波速在高频时甚至低于钻铤横波速度.这种频散特性和多阶模式特性,是径向多分层开波导结构的导波属性.  相似文献   

Effect of waves on cavitation and pressure pulses of a tanker with twin podded propulsion     

《Applied Ocean Research》2017

There is increasing interest in optimizing ships for the actual operating condition rather than just for calm water. In order to optimize the propeller designs for operations in waves, it is essential to study how the propeller performance is affected by operation in waves. The effect of various factors that influence the propeller is quantified in this paper using a 8000 dwt chemical tanker equipped with twin-podded propulsion as a case vessel. Propeller performance in waves in terms of cavitation, pressure pulses, and efficiency is compared with the performance in calm water. The influence of wake variation, ship motions, RPM fluctuations and speed loss is studied. Substantial increase in cavitation and pressure pulses due to wake variation in the presence of waves is found. It is found that the effect of other factors is relatively small and easier to take into account as compared to wake variation. Therefore, considering the wake variation at least in the critical wave condition (where the wavelength is close to ship length) in addition to calm water wake is recommended in order to ensure that the optimized propeller performs well both in calm water and in waves.  相似文献   

Analytical investigation of hydrodynamic performance of a dual pontoon WEC-type breakwater     

《Applied Ocean Research》2017

Based on the linear potential flow theory and matching eigen-function expansion technique, an analytical model is developed to investigate the hydrodynamics of two-dimensional dual-pontoon floating breakwaters that also work as oscillating buoy wave energy converters (referred to as the integrated system hereafter). The pontoons are constrained to heave motion independently and the linear power take-off damping is used to calculate the absorbed power. The proposed model is verified by using the energy conservation principle. The effects of the geometrical parameters on the hydrodynamic properties of the integrated system, including the reflection and transmission coefficients and CWR (capture width ratio, which is defined as the ratio of absorbed wave power to the incident wave power in the device width). It is found that the natural frequency of the heave motion and the spacing of the two pontoons are the critical factors affecting the performance of the integrated system. The comparison between the results of the dual-pontoon breakwater and those of the single-pontoon breakwater shows that the effective frequency range (for condition of transmission coefficient K_T < 0.5 and the total capture width ratio η_total > 20%) of the dual-pontoon system is broader than that of the single-pontoon system with the same total volume. For the two-pontoon system, the effective frequency range can be broadened by decreasing the draft of the front pontoon within certain range.  相似文献   

黑龙江省土壤湿度及其对气温和降水的敏感性分析   总被引：3，自引：0，他引：3       下载免费PDF全文

王丹  南瑞  韩俊杰  高永刚  李秀芬  孙彦坤 《气象与环境学报》2012,28(2):49-53

气温和降水量变化是影响土壤湿度变化的主要原因,研究土壤湿度对气温和降水的敏感性对区域农业生产、生态环境治理和经济可持续发展有重要意义。采用1984-2007年黑龙江省73个气象观测站的气温、降水数据和13个土壤湿度观测站土壤观测数据,利用EOF、相关分析等数理分析方法,对黑龙江省土壤湿度与气温、降水量之间的关系进行了研究。结果表明：1984-2007年黑龙江省土壤湿度变化在不同区域存在差异：除三江平原中西部地区外,大部分农区土壤湿度变化趋势一致,20世纪90年代中期以前基本偏湿,而90年代中期以后则为偏干,2001年偏干严重。土壤湿度对气候变化响应的敏感性也不同,松嫩平原（西南部除外）是土壤湿度对气温和降水变化敏感区域;松嫩平原西南部对气温敏感;伊春南部地区-哈尔滨东部-三江平原西部为降水敏感区;逊克、伊春北部、牡丹江和三江平原东部土壤湿度对气温和降水均不敏感。  相似文献