Methods for ultimate limit state assessment of ships and ship-shaped offshore structures: Part I—Unstiffened plates

The present paper is Part I of a series of three papers prepared by the authors on the methods useful for ultimate limit state assessment of marine structures, that have been developed in the literature during the last few decades. It is considered that such methods are now mature enough to enter day-by-day design and strength assessment practice. The aims of the three papers are to conduct some benchmark studies of such methods on ultimate limit state assessment of (unstiffened) plates, stiffened panels, and hull girders of ships and ship-shaped offshore structures, using some candidate methods such as ANSYS nonlinear finite element analysis (FEA), DNV PULS, ALPS/ULSAP, ALPS/HULL, and IACS common structural rules (CSR) methods. As an illustrative example, an AFRAMAX-class hypothetical double hull oil tanker structure designed by CSR method is studied. In the present paper (Part I), the ultimate limit state assessment of unstiffened plates under combined biaxial compression and lateral pressure loads is emphasized using ANSYS, DNV PULS, and ALPS/ULSAP methods, and their resulting computations are compared. Part II will deal with methods for the ultimate limit state assessment of stiffened panels under combined biaxial compression and lateral pressure using ANSYS, DNV PULS, and ALPS/ULSAP methods, and Part III will treat methods for the progressive collapse analysis of the hull structure using ANSYS, ALPS/HULL, and IACS CSR methods.     

Detecting the intertidal morphologic change using satellite data

Previous research has suggested that competitive bottlenecks may exist for the Mediterranean grey mullets (Osteichthyes, Mugilidae) at the fry stage with the exotic Cyprinus carpio (Osteichthyes, Cyprinidae) playing a central role. As a consequence, the structure of grey mullet assemblages at later stages is thought to reflect previous competition as well as differences in osmoregulatory skills. This paper tests that hypothesis by examining four predictions about the relative abundance of five grey mullet species in 42 Western Mediterranean estuary sites from three areas (Aiguamolls de l'Empordà, Ebro Delta and Minorca) differing in the salinity level and occurrence of C. carpio. Field data confirmed the predictions as: (1) Liza aurata and Mugil cephalus were scarce everywhere and never dominated the assemblage; (2) Liza saliens dominated the assemblage where the salinity level was higher than 13; (3) Liza ramado always dominated the assemblage where the salinity level was lower than 13 and C. carpio was present; and (4) Chelon labrosus dominated the assemblage only where the salinity level was lower than 13 and C. carpio was absent. The catch per unit effort of C. labrosus of any size was smaller in the presence of C. carpio than where it had not been introduced, which is in agreement with the juvenile competitive bottleneck hypothesis. Discriminant analysis confirmed that the assemblage structure was linked to the salinity level and the occurrence of C. carpio for both early juveniles and late juveniles as well as adults. The data reported here reveal that the structure of grey mullet assemblages inhabiting Mediterranean estuaries is determined by salinity and competitive interactions at the fry stage.     

北京奥运赛期温、湿、风、云、雨的气候信息分析

分析北京城近郊区奥运会赛场临近的气象台站(南郊观象台、朝阳站、海淀站、丰台站、石景山站)1995～2004年10年8月的气温、相对湿度、风向风速、低云量、降水量等5个气象要素的气候变化,结果表明:1)19～22日有2次阴雨天气过程,气温下降幅度较大;2)5个台站的主导风向是S-SE,逐日平均风速的峰值出现在16时(北京时间),其值为2.0～3.1m.s-1;3)白天各雨量等级合计≥35%的频率出现5天;4)奥运会开幕时间(2008年8月8日20时),晴天到少云的频率占90%,阴天为10%,无雨为80%。这种气候特点为奥运会组委会、参赛运动员和观众提供了赛场环境5个气象要素的日变化规律。同时,对于奥运会的短期气象服务也有一定的参考价值。     

陡倾层状岩质边坡动力响应大型振动台模型试验研究

结合 5·12 汶川地震诱发的大量次生地质灾害,设计并完成了比例为1 :100的边坡大型振动台模型试验,讨论了相似关系和模型的设计、传感器的布置、模型的建造过程,编制了动荷载加载制度。试验结果表明,边坡对输入动荷载具有放大作用,沿坡面向上,PGA放大系数呈上升趋势,并具有一定的节律性,其节律性变化规律受坡体岩性、结构面组合和动荷载振动方向的影响; 动荷载X向振动时的坡面峰值重力加速度(PGA)放大系数明显大于Z向振动时的坡面PGA放大系数,说明坡体在X向振动时的动力响应更为强烈; 坡体内PGA放大系数在铅直向上呈线性放大,在水平向上表现为节律性变化。试验结果有助于了解陡倾层状岩质边坡在不同动荷载作用下的响应规律,对研究其变形失稳机制和抗震结构设计提供了依据。     

基于正常轮廓更新的自适应异常检测方法

根据网络系统发生正常改变的基本特征,提出了确定网络系统正常改变的“三条件”计算方法,其计算结果可作为更新正常轮廓的依据。对正常轮廓的更新问题进行了深入探讨,提出了自适应异常检测的实现机制。并以网络流量分析为例,验证了在异常检测中应用这一方法的可行性。     

基于数据挖掘技术的白水河滑坡多场信息关联准则分析

为探究滑坡多场监测数据间的关联准则,采用数据挖掘技术中的两步聚类法与Apriori算法,开展滑坡多场信息关联准则研究。以三峡库区白水河滑坡为例,分析ZG93监测点于2003年6月—2016年12月期间的监测数据,选取影响滑坡变形的主要诱发因子,采用两步聚类法对不同的影响因子进行预聚类和聚类,将数值型变量转化为离散型变量后,应用Apriori算法进行处理,生成满足最小置信度的关联准则,建立白水河滑坡多场耦合作用模式下的影响因子与滑坡位移变形关联准则判据。研究表明,关联准则对于滑坡灾害的变形分析具有重要的意义,数据挖掘技术可较好地应用于三峡库区地质灾害位移预测预报中。     

黔北新仁地区上二叠统龙潭组煤质地球化学特征及聚煤规律

根据黔北新仁地区上二叠统龙潭组煤样的主量元素、微量元素、工业分析、硫分及灰分分析数据,评价了该地区晚二叠世煤的总体煤质特征;在此基础上重点探讨了煤中硫分和灰分与成煤环境的联系。结果表明,黔北新仁地区上二叠统龙潭组煤中SiO2、TiO2、K2O含量较高,其中SiO2是全国煤的6倍,TiO2是全国煤的7倍,K2O是全国煤的10倍;其余氧化物含量均是全国煤的1~4倍。新仁地区上二叠统龙潭组中煤的球粒陨石标准化稀土元素配分曲线除样品PM403-MY3、MY8以外,其他各煤样稀土元素分布模式相似,整体上呈左高右低的宽缓的“V”型曲线,（La/Yb）N为5.27~18.34,均值为8.91,表明轻重稀土元素分馏程度高的特征;δEu为0.38~1.52,均值为0.74,具有显著的负Eu异常。新仁地区煤炭资源具有高全水分、中-高灰分、低-中高挥发分、特低和低硫分、低固定碳、低磷分、特低氯等特征。此外,煤中灰分产率、煤灰成分指数以及灰成分三端元分析均揭示聚煤环境为从陆源区水浅、水动力较强而还原性较弱的环境,向远离陆源区水深、水动力较弱而还原性较强的环境变化,与全硫分分析的结论相一致。综合分析认为,新仁地区晚二叠世聚煤规律的主控地质因素为构造运动,与峨眉山玄武岩、古气候、沉积环境等因素有关。     

海南省琼中县花岗岩地区含水层电性特征及地下水赋存规律

海南省琼中县侵入岩分布广泛,历经白垩纪、侏罗纪、三叠纪、二叠纪侵入期,以花岗岩、花岗闪长岩为主。地质构造相对不发育,岩体完整性好,岩石结构致密,地下水富水性差异大,找水难度大。在地质调查、物探勘探、水文钻探相互验证的基础上,较系统地分析了花岗岩区断裂构造裂隙水、风化壳网状裂隙-孔隙水和接触带型基岩裂隙水3种地下水类型的赋存规律及含水层电性特征。研究结果表明,断裂构造裂隙水主要赋存于构造破碎带中,尤其是走向北西的张性或张扭性构造带中,一般富水性好,水量大;风化壳网状裂隙-孔隙水分布普遍,多赋存于沟谷或山间凹谷地貌的风化壳中,一般富水性差,水量小;接触带型基岩裂隙水主要赋存于花岗岩与沉积岩、花岗岩与变质岩、不同侵入期次花岗岩接触带上,富水性差异大。在视电阻率等值线断面上,花岗岩断裂构造裂隙水呈现为陡降低阻"条带"或"漏斗"状异常电性特征曲线;花岗岩风化壳网状裂隙-孔隙水呈现为"洼地"或"凹槽"状低阻电性特征;接触带型基岩裂隙水呈现为"层"或"带"状低阻电性特征曲线。     

湖南崇阳坪地区沙溪钨矿床地质特征及找矿前景分析

沙溪钨矿床是近年来在崇阳坪地区新发现的一个产于中华山岩体接触带内的矿床,其资源量有望达大型规模。本文通过大量的野外资料,在现有勘查成果的基础上,对矿床的地质特征、矿化富集规律、找矿标志及找矿前景进行了分析研究,初步认为矿区钨矿化具有分段富集的现象,富集部位与含脉密度增大、云英岩化增强等部位吻合,且从地表浅部向深部,在一定程度上表现出细脉变多、矿化加强的趋势,已发现矿体深部很有可能存在厚大的钨矿体,找矿前景较好。     

基于DFOS的边坡多场信息关联规则分析

采用分布式光纤传感技术(DFOS),可获得边坡多场分布信息,但如何对海量的多场信息进行相关分析,正确评价多场耦合作用下的边坡稳定性,仍是一项十分复杂的工作。本文首先介绍了数据挖掘中关联规则分析方法的基本原理,设计了边坡应变场、变形场、渗流场、温度场和环境参量等多场信息DFOS的获取方案,并以三峡库区马家沟边坡为例,对DFOS获得的边坡多场监测数据进行了关联规则分析,揭示了监测时间与库水位涨落、库水位涨落与坡体前缘地下水位间的关联性,并与实际监测数据进行了比较,证明了采用关联规则方法对DFOS边坡多场信息分析的有效性,从而为边坡稳定性评价和滑坡预测预警提供了科学依据。