Parametric Resonance Analyses for Spar Platform in Irregular Waves

The parametric instability of a spar platform in irregular waves is analyzed. Parametric resonance is a phenomenon that may occur when a mechanical system parameter varies over time. When it occurs, a spar platform will have excessive pitch motion and may capsize. Therefore, avoiding parametric resonance is an important design requirement. The traditional methodology includes only a prediction of the Mathieu stability with harmonic excitation in regular waves. However, real sea conditions are irregular, and it has been observed that parametric resonance also occurs in non-harmonic excitations. Thus, it is imperative to predict the parametric resonance of a spar platform in irregular waves. A Hill equation is derived in this work, which can be used to analyze the parametric resonance under multi-frequency excitations. The derived Hill equation for predicting the instability of a spar can include non-harmonic excitation and random phases. The stability charts for multi-frequency excitation in irregular waves are given and compared with that for single frequency excitation in regular waves. Simulations of the pitch dynamic responses are carried out to check the stability. Three-dimensional stability charts with various damping coefficients for irregular waves are also investigated. The results show that the stability property in irregular waves has notable differences compared with that in case of regular waves. In addition, using the Hill equation to obtain the stability chart is an effective method to predict the parametric instability of spar platforms. Moreover, some suggestions for designing spar platforms to avoid parametric resonance are presented, such as increasing the damping coefficient, using an appropriate RAO and increasing the metacentric height.     

一种基于Partial EIV模型的圆曲线拟合解法

针对圆曲线拟合问题,以圆曲线的参数方程为基础建立圆曲线拟合的EIV模型,根据系数矩阵的特点将模型转化为更合理的Partial EIV模型,通过公式变形为最小二乘形式,采用两步迭代法求解模型参数,保证系数矩阵中相同元素的改正数一致,常数元素的改正数为零。算例数据结果表明,所提算法的可行性、拟合精度相对较优。     

江南古陆南缘四堡群同位素地质年代学研究

四堡群浅变质火山-沉积岩系主要出露于桂九万大山地区，是华南最古老的地层单元之一。对坛地区罗布山枕状玄武岩中细粒原生锆石进行单颗粒锆石蒸节-沉积法年龄测定，两组锆石样品获得207Pb/206Pb年龄分别为1374±20（2σ）Ma和1863±7（2σ）Ma。对宝坛地区基性和超基性火山岩进行了Sm-Nd同位素研究，获等时线年龄为1782±820（2σ）Ma，与锆石单颗粒207Pb/206Pb年龄一致，充分说明四堡群形成于中元古代早期。火山岩的εNd（t）为0.6，表明基性-超基性岩浆源自于亏损地幔。这套岩石的     

夕卡岩矿床研究的某些重要新进展

夕卡岩矿床是一种具有重要工业意义的矿床类型，是世界上富铁矿，钨、锡、铋、铅锌，金和金云母，透辉石，硅灰石等金属和非金属矿产的重要来源。这类矿床不仅分布广泛，矿物组合特殊，而且包含有内生成矿作用许多复杂的成因信息。因此，一个多世纪以来国际上对夕卡岩矿床的研究长盛不衰，不断有所创新，文章回顾了近二十年来，在成矿的构造背景，矿床的多成因性，岩浆期和岩浆夕卡岩，碱交代与成矿，交代分带，含银铅锌锰质夕卡岩，含金夕卡岩和夕卡岩含矿性评价标志等方面新的研究进展。     

甘肃省M739铁矿床经济意义概略研究

通过运用静态评价方法对M739铁矿床经济上的合理性、盈利性,实施上的可能性、风险性进行概略研究,以期为矿床开发投资决策提供依据。     

风速随高度变化的曲线拟合

运用SPSS11.5统计软件包,对双水镇风速随高度变化规律分别作对数曲线、逆曲线、二次曲线、幂函数曲线、S曲线和指数曲线的参数估计.结果表明,在高度＜900 m的低空下,幂函数的曲线解释量R2最高、标准误差S.E最小,其拟合效果最好.     

中国海洋生物研究70年

随着中国“海洋强国”战略的提出,加快建设海洋类学科的发展成为历史必然,海洋生物是海洋不可分割的一部分,海洋环境和生物相互依存,相互作用,海洋生物研究重要性日益凸显。为纪念中国科学家在海洋生物领域的突出贡献,本文回顾了建国以来中国海洋生物相关的重要研究进展,梳理了中国科学家在海洋生物领域的突出贡献,系统总结并讨论了未来研究方向,抛砖引玉,希望籍此助推中国海洋生物研究的新高潮。     

Geographic perspectives on urban sustainability: past,current, and future research trajectories

ABSTRACT

The 21st century has been called the “century of the city” and compounded concerns that current development pathways were not sustainable. Calls for scholarship on urban sustainability among geographers cites strengths in the human-environment and urban subfields that positioned the discipline to make unique contributions to critical research needs. This special issue reflects on the contributions that geographers have made to urban sustainability scholarship. We observe that that integration across human-environment and urban subfields reflects broader bifurcations between social theory and spatial science traditions in geography. Piggy-backing on the rise of sustainability science, the emergence of urbanization science compels geographers to reflect upon the ways in which we are positioned to make unique contributions to those fields. We argue that those contributions should embrace systems thinking, empirically connect social constructs to biophysical patterns and processes, and use the city as a laboratory to generate new theories.     

Equilibrium,Thermodynamic, and Kinetic Studies on Lead (II) Biosorption from Aqueous Solution by Saccharomyces cerevisiae Biomass

This paper presents a biosorption procedure for the preconcentration of Pb²⁺ ions using Saccharomyces cerevisiae biomass. The influence of several factors including pH, biomass dosage, contact time, and temperature on biosorption efficiency were optimized. At optimum value of all the equilibrium, thermodynamic, and kinetic parameters of Pb²⁺ ion biosorption was investigated by testing the Langmuir and Freundlich models and first and second order kinetic models were applied. The biosorption capacity of S. cerevisiae biomass was determined 89.6 mg/g, while the retained Pb²⁺ ions by S. cerevisiae were reversibly eluted using 5 mol/L HNO₃. Due to the high stability of S. cerevisiae the applied biomass can be used successively ten times with a slightly decrease (about 20%) in the recovery of Pb²⁺ ions. The calculated thermodynamic parameters, ΔG°, ΔH°, and ΔS° showed that the biosorption of Pb²⁺ ion onto S. cerevisiae biomass was feasible, spontaneous, and endothermic under examined conditions. The results of kinetic analysis showed that the biosorption processes of Pb²⁺ ions onto S. cerevisiae biomass followed pseudo second order kinetics.     

Development of a portable field rainfall simulator for use in hillside vineyard runoff and erosion studies

An inexpensive, mobile field rainfall simulator and runoff plot frame were developed for use on hillside vineyards. The simulator framework and components were lightweight, readily available and easily manageable such that they can be handled by one person during transport, set–up and operation. The vineyard rainfall simulator was simpler than many of the machines in recent use for similar studies, yet offered equal or improved performance for small‐plot studies. The system developed consistent sized 2·58 mm raindrops at intensities ranging from 20 to 90 mm/h. The average distribution uniformity coefficient at an intensity of 60 mm/h was 91·7%, with a deviation of only 2·2%. This coefficient was similar to the range reported for a more complex rotating disk simulator, and was notably greater than that obtained for other similar devices. The system water capacity of 40 l allowed for 1‐h storm durations at 60 mm/h, usually sufficient time for commencement of erosion and runoff. The runoff plot frame was designed to be quickly installed, and to discourage sediment deposition in the routing of runoff to collect containers. Copyright © 2000 John Wiley & Sons, Ltd.