Discrete modeling of strain accumulation in granular soils under low amplitude cyclic loading

An advanced understanding of the strain accumulation phenomenon in granular soils subjected to low amplitude cyclic loading with relatively high frequency is needed to enhance the ability to predict the settlement of granular soils induced by vibrations. In the current study, the discrete element method is used to study this phenomenon. A loose and a medium dense sample composed of a relatively large number of spheres are considered. A series of stress controlled cyclic triaxial tests with different excitation amplitudes and frequencies is performed on these samples at different static stress states. The response of these samples at the macroscopic and microscopic scales is analyzed. The sample density, the cyclic stress amplitude and the static stress state importantly affect strain accumulation. However, the cyclic excitation frequency has a small effect on strain accumulation. At the microscopic scale, frictional sliding occurring at a few contacts continuously dissipates energy and the fraction of these contacts varies periodically during cyclic loading. The coordination number of these samples increases slightly as strain accumulates. However, the anisotropy remains almost constant during low amplitude cyclic excitation. A qualitatively good agreement between numerical and experimental results is found.     

南黄海盆地“三明治”结构的页岩气保存条件探讨

为了促进南黄海盆地中-古生界页岩气勘探的早日突破,开展了美国福特沃斯盆地巴奈特页岩气藏、四川盆地页岩气藏以及贵州潜在页岩气藏保存条件的对比研究。结果显示,“三明治”结构的保存条件在页岩气成藏中至关重要,其中,“三明治”结构是指泥岩/页岩层与其顶、底板的灰岩/白云岩层构成的一种很好的储-盖组合。结合下扬子中-古生界发育特征以及南黄海崂山隆起所具有的古生代构造变形弱且隆起两侧边缘存在逆冲断层封堵等条件认为,南黄海盆地下寒武统和二叠系很可能存在“三明治”结构的页岩气保存条件,是南黄海页岩气获得突破的关键层段;而崂山隆起两侧边缘很可能是页岩气钻探的首选目标。     

云南孟连西7.3级、武定6.5级、丽江7.0级三次强震前地震波振幅比的时空演化特征

１９９５年７月１２日至１９９６年２月３日短短７个月,云南地区连续发生了孟连西中缅边境７．３级、武定５．５级、丽江７．０级３次强震,本文研究了近期这几次强震前５个地震台地震图垂直分量Ｓ、Ｐ波最大振幅比的时空演化特征,动态追踪了振幅比明显偏离平稳态的突变过程。发现主震前５—８年,７级大震震中１００ｋｍ范围出现振幅比高（低）值突变,６级强震震中１３０ｋｍ范围出现振幅比高值突变,当振幅比的突变在缓升（降）的背景上骤升（降）,或突变异常的地震次数明显增加,则中长期异常进入中短期阶段。在强震震中１３０ｋｍ范围内的地震台（近台）振幅比值高达１５．２以上,而远离强震震中２５０ｋｍ以外的地震台（远台）振幅比最大值仅为９．８,近台的突变幅度至少比远台大３０％。而强震成组发生前一年半时间内,位于强震震中１１０ｋｍ范围内的近台振幅比的突变幅度比远在２５０ｋｍ外远台大５５—７５％。对振幅比的突变和时空演化特征从非线性动力学模型和模拟实验结果进行了初步成因探讨。     

流化冰对于鲣鱼的保鲜效果研究

以远洋鲣鱼为研究对象,以传统淡水碎冰保鲜为对照,研究流化冰处理对鲣鱼的理化性质及微生物特性的影响。结果表明:(1)–4°C冷藏18d后,流化冰保鲜鱼肉pH值、TVB-N、TBA、a*值和菌落总数依次为5.57、10.2mgN/100g、2.87mg/100g、8.92和2.61lgCFU/g,而淡水碎冰保鲜鱼肉各指标已达6.05、20.3mgN/100g、6.60mg/100g、7.16和3.02lgCFU/g,故可知流化冰保鲜处理效果明显优于碎冰保鲜。(2)在25±1°C室温条件下,将冰与鱼放入保温箱内保鲜8h后,流化冰保鲜鱼肉的a*值、pH值、TVB-N、TBA、菌落总数和汁液流失率均显著低于空白和淡水碎冰保鲜处理组(P0.05)。流化冰保鲜可显著减缓鱼体的腐败进程、延长产品货架期,进而满足冰鲜水产品的远洋及长距离运输要求。     

基于局部回波幅值统计的海杂波背景下小目标检测

针对传统舰载雷达和岸基雷达很难检测出海杂波背景下小目标的现状,提出一种基于局部回波幅值统计的方法来检测海杂波背景下小目标.该算法基于数学统计思想:计算不同距离单元海杂波的幅值的最大值和标准偏差,分析发现距离单元含有小目标回波的最大幅值明显小于其它距离单元只含有海杂波回波的最大幅值,距离单元含有小目标回波的幅值的标准偏差明显大于距离单元只含有海杂波回波的幅值的标准偏差,因此可以在对小目标没有任何先验知识条件下,较准确地检测出海杂波背景下的小目标.实验证明,该算法是有效的.     

利用温度链对南海内波振幅的观测

内波的实测资料一般为走航或者浮标布站观测得到的一个关于时间和空间的大面资料,将此资料进行滤波后,进行简单的数值处理,即可得到内波的振幅。但是这种资料较少,布控站位难度较大,成本也较高,是一种不易获取的资料。本文利用的温度链资料是一种获取简单,成本也较低的实测资料。利用温度链资料基于内波带动水质点上下波动的物理过程,进行内波振幅的计算,将会有较大的适用性。     

鄂尔多斯盆地中生界低幅度构造岩性圈闭油气储层预测技术

鄂尔多斯盆地天环向斜中生界油气储层为低幅度构造背景下的砂岩岩性圈闭储层,与围岩波阻抗差小,常规的地震储层预测方法精度低。针对储层的地质地球物理特征,提出了地震地层分析与物性反演的储层预测技术方案,提高了储层预测精度。     

Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part I: Amplitudes

The Indian Ocean tsunami of December 26, 2004, not only affected the Bay of Bengal coast of India but also part of the Arabian Sea coast of India. In particular, the tsunami caused loss of life and heavy damage on some parts of the Kerala coast in southwest India. The tsunami traveled west, south of Sri Lanka, and some of the tsunami energy was diffracted around Sri Lanka and the southern tip of India and moved northward into the Arabian Sea. However, tsunami, being a long gravity wave with a wave length of a few hundred kilometers, has to take a wide turn. In that process, it missed the very southern part of the Kerala coast and did not achieve large amplitudes there. However, further north, the tsunami achieved amplitudes of upto 5 m and caused loss of life and significant damage. Here we identify the physical oceanographic processes that were responsible for selective amplification of the tsunami in certain locations.