基于分区间泛化Kriging近似模型的船舶局部结构形状优化     

张干锋  王德禹 《海洋工程》2018,36(6):46-57

为提高Kriging近似模型在船舶结构性能多维度响应预测方面的适用性,对常规Kriging近似模型进行分区间泛化改进:一是对设计样本点的各个维度(分量)进行划区,并在每一个分区间内采用最优拉丁超立方(OLhd)取样;二是引入比例系数w1组合高斯与指数型相关函数提高模型对数据的泛化能力,从而在每个划分的区间内建立泛化的Kriging近似模型。通过SCH测试函数,验证了构造的分区间泛化Kriging模型有效性。结合参数化建模和改进Kriging近似模型对某过渡肘板和舱口角隅边界进行形状优化,优化第一阶段由改进的近似模型通过多岛遗传算法得到全局初步的最优解,第二阶段在初步解的基础上缩小优化变量范围,由少量的FEM计算即可在小范围内搜寻到精确的最优设计变量。结果表明:分区间泛化Kriging近似模型在预测多维度响应时较常规Kriging模型预测精度更高;分阶段的形状优化流程在保证极小误差和缩小计算成本的情况下能够得到理想的应力分布和重量优化结果,有助于船舶结构的轻量化研究。  相似文献   

基于等角比例投影的球面三角四叉树剖分模型   总被引：4，自引：1，他引：3  

袁文 《遥感学报》2009,13(1):103-111

将人不可及的观测统称为遥感,使地面传感器成为遥感的一部分.提出遥感科学与技术的基本内容,包括传感器研制、遥感数据获取、数据处理、信息提取和应用5个部分.其理论基础是辐射传输过程模拟与反演,贯穿于各个组成部分.数据的可视化及传输发布存在于从数据获取到应用的各个环节.遥感科学与技术正处于快速发展时期,各个方面都有前沿问题.辐射传输理论中的尺度和多角度问题,地形对辐射和图像几何影响及相应的多源多时相数据的匹配问题,遥感信息提取中自动化和目视解译的结合以及信息提取新策略问题,遥感与基于过程模拟的气候一水文-生态模式相结合的四维数据同化技术等是当前遥感科学与技术发展中的重要学科前沿.四维数据同化技术是突破遥感瞬时信息获取、实现图像与机理模型有机结合、改善自身数据产品质量和促进地学大范围模拟准确性的重要发展方向,能增强遥感对全球变化科学的贡献.  相似文献   

基于Voronoi图的人口普查区的划分技术研究   总被引：1，自引：0，他引：1  

冯亮  刘德钦  马维军 《测绘科学》2009,34(2)

人口普查区的划分是进行人口普查的先期工作。本文探讨了利用Voronoi图的良好空间拓扑属性进行人口普查区划分的方法。文章从多边形数据出发,利用间接法实现Voronoi图的生成,然后根据普查区划分的人口阀值,通过相邻Voronoi图之间的操作,最终实现人口普查区的划分。可为人口普查提供有效的服务,并间接地为人口空间化提供了一种有效的表现形式。  相似文献   

一种基于信息网格的空间数据分解算法     

胡斌  刘鹏  陈正阳 《地理信息世界》2007,5(4):40-44

针对空间数据库数据海量且分布的特点,为了能从这些空间数据中更加有效的收集信息和发现知识,介绍了基于信息网格的空间数据挖掘计算模型,在分析空间数据划分一般原则和方法的基础上,针对该计算模型给出了一个数据划分的初步算法,并通过模拟实验对算法的时间性能进行了评价与分析。  相似文献   

基于机器学习的格点气温预报订正方法     

方鸿斌  王珊珊  王晓玲  谭江红  鲁礼炳 《气象》2024,50(1):103-114

使用2017年9月至2021年3月国家级业务化运行的智能网格实况分析产品和欧洲中期天气预报中心全球模式(EC)产品,根据湖北省的地理分布特征构建6个分区,采用基于LightGBM机器学习算法建立的气温预报方法,生成湖北省0.05°×0.05°格点气温预报产品。利用2021年4—9月的预报产品和格点实况资料进行检验,结果表明:基于机器学习的气温预报方法(MLT)取得了较好的预报效果,其在0～72 h时效内优于中央气象台下发的气温精细化指导预报(SCMOC)和EC产品;MLT在山区的误差较平原大,但山区的订正幅度大于平原,日最高气温的订正幅度大于日最低气温的订正幅度;4—9月MLT、SCMOC、EC产品的平均绝对误差(MAE)日变化都呈现了白天偏高、夜间偏低、午后凸起的单峰特征,MLT的MAE值较SCMOC和EC产品的更低,并且在转折性天气中仍具有优势;站点检验与格点检验结论一致,基于格点建模的气温预报产品对站点预报同样得到了订正。机器学习在格点气温的模式订正方面可以作为一个行之有效的手段。  相似文献   

The Partitioning of Tungsten bwtween Aqueous Fluids and Silicate Melts     

Xu Yongsheng  Zhang Benren  Han Yinwen 《中国地球化学学报》1993,12(2):128-136

An experimental study has been carried out to determine the partition coefficients of tungsten between aqueous fluids and granitic melts at 800 °C and 1.5 kb with natural granite as the starting material. The effects of the solutions on the partition coefficients of tungsten show a sequence of P > CO ₃ ²⁻ > B > H₂O. The effects are limited (generallyK _D < 0.3) and the tungsten shows a preferential trend toward the melt over the aqueous fluid. The value ofK _D increases with increasing concentration of phosphorus; theK _D increases first and then reduces with the concentration of CO ₃ ²⁻ when temperature decreases, theK _D between the solution of CO ₃ ²⁻ and the silicate melt increases, and that between the solution of B₄O ₇ ²⁻ and the silicate melt decreases. The partition coefficients of phosphorus and sodium between fluids and silicate melts have been calculated from the concentrations of the elements in the melts. TheK _D value for phosphorus is 0.38 and that for sodium is 0.56. Evidence shows that the elements tend to become richer and richer in the melts.  相似文献   

基于自适应四叉树分割的遥感图像压缩算法   总被引：4，自引：0，他引：4  

倪林 《遥感学报》2002,6(5):343-351

遥感图像具有不同于一般图像的特点,针对遥感图像对压缩算法的特殊要求,提出了自适应四叉树分割算法实现图像的分块,以各像块的均值近似表示该像块的灰度值,从而以尺量少的数值获得对原始图像的最佳逼近,再对辐近误差进行自适应分割和基于像块方差的自适应量化,最后对各分量进行Huffman编码.实验表明,本算法能表现出良好的实用性能,比JPEG算法更适用于遥感图像的压缩.  相似文献   

川滇强震的回归—马尔可夫链联合预测     

张启明 《四川地震》1993,(1):40-43

本文应用回归—马尔可夫链联合预测地震的方法,结合川、滇强震的特点,对川、滇强震进行了计算,并作了预测验证。结果表明,该方法对川、滇强震的预测效果较好。  相似文献   

Equilibrium Evaporation and the Convective Boundary Layer   总被引：2，自引：1，他引：1  

M. R. Raupach 《Boundary-Layer Meteorology》2000,96(1-2):107-142

A theory is developed for surface energy exchanges in well-mixed, partlyopen systems, embracing fully open and fully closed systems as limits.Conservation equations for entropy and water vapour are converted intoan exact rate equation for the potential saturation deficit D in a well-mixed, partly open region. The main contributions to changes in D arise from (1) the flux of D at the surface, dependent on a conductance g_q that is a weighted sum of the bulk aerodynamic and surface conductances; and (2) the exchange flux of D with the external environment by entrainment or advection, dependent on a conductance g_e that is identifiable with the entrainment velocity when the partly open region is a growing convective boundary layer (CBL). The system is fully open when g_e/g_q , and fully closed when g_e/g_q 0. The equations determine the steady state surface energy balance (SEB) in a partly open system, the associated steady-state deficit, and the settling time scale needed to reach the steady state. The general result for the steady-state SEB corresponds to the equations of conventional combination theory for the SEB of a vegetated surface, with the surface-layer deficit replaced by the external deficit and with g_q replaced by the series sum (g_q ^-1 + g_e ^-1)^-1. In the fully open limit D is entirely externally prescribed, while in the fully closed limit, D is internally determined and the SEB approaches thermodynamic equilibrium energy partition. In the case of the CBL, the conductances g_q and g_e are themselves functions of D through short-term feedbacks, induced by entrainment in the case of g_e and by both physiological and aerodynamic (thermal stability) processes in the case of g_q. The effects of these feedbacks are evaluated. It is found that a steady-state CBL is physically achievable only over surfaces with at least moderate moisture availability; that entrainment has a significant accelerating effect on equilibration; that the settling time scale is well approximated by h/(g_q + g_e), where h is the CBL depth; and that this scale is short enough to allow a steady state to evolve within a semi-diurnal time scale only when h is around 500 m or less.  相似文献   

Spatio-temporal changes in the abundance of the populations of the gastrotrich community in a shallow lake of tropical Africa     

Serge H. Zbaz Togouet  Thomas Njine  Norbert Kemka  Moise Nola  Samuel Foto Menbohan  Walter Koste  Claude Boutin  Rick Hochberg 《Limnologica》2007,37(4):311-322

Studies on the biodiversity and population dynamics of freshwater planktonic Gastrotricha have been carried out in conjunction with a physical–chemical analysis of the water in the Yaounde Municipal Lake (Cameroon, Central Africa) over a 14 months period (November 1996–December 1997). The results obtained allow to consider the Yaounde Municipal Lake as an eutrophic lake. It harbours eight species of Gastrotricha belonging to four genera (Chaetonotus, Dasydytes, Neogossea and Polymerurus) of the order Chaetonotida. This community was characterized by high abundances of populations, and was dominated by the genus Neogossea and Chaetonotusreaching up to 2000 ind. L⁻¹. Polymerurus was mostly abundant at the almost anoxic bottom layers. The highest abundances were found mostly during the rainy season, when there is an important sedimentation process of organic matter, and were influenced by several different environmental factors such as dissolved oxygen, temperature and pH of the water.

Finally this community which may play an important role in the water bodies, is a potential water quality indicator.  相似文献