确定海洋平台钢裂纹扩展曲线的快速方法

提出了一种确定海洋平台钢裂纹扩展曲线的快速方法。该方法可以综合利用以往的经验数据和当前试验数据确定表面疲劳裂纹扩展速率曲线。与传统的只能利用当前试验数据确定表面疲劳裂纹扩展速率曲线相比。其可利用信息量大幅度增加,所以在精度相同的情况下,可以节省大量试件;而且在试样数一定的情况下。又可大大提高预测精度。文中还给出了海洋平台钢试验对比实例。     

Laboratory study on cement admixed marine silt bricks

For the purpose of efficient utilization of sediments dredged from harbor, a new method was proposed in this study. Marine silt bricks were made by mixing sediments with cement and gypsum, placing it in a cubic mold with 240 mm in length, 115 mm in width, and 53 mm in height, and curing for certain days. To investigate the effects of cement and initial water content of soil on the mechanical behavior of marine silt bricks, unconfined compressive and flexural strength tests were carried out. Given the same curing time and cement content, the higher the initial water content, the lower the compressive and flexural strength. After 60 days of curing, the compressive strength of marine silt bricks with cement content = 20% and water content = LL (liquid limit) reached approximately 5 MPa. The flexural strength was relatively low. The flexural strength of marine silt bricks with 20% cement and water content = LL was around 1.5 MPa. The compressive and flexural strength decreased with the increase of water/cement ratio. As for the curing time, longer curing time had a positive impact on the compressive strength. The ratio of flexural to compressive strength varied slightly in the range of 0.4–0.5.     

Model tests on installation and extraction of suction caissons in dense sand

A series of model tests were performed on steel- and Perspex-made suction caissons in saturated dense marine sand to explore installation and extraction behaviors. The extractions of the caisson were conducted by applying monotonic loading or by pumping water into the caisson. Responses of suction caissons to pullout rates, aspect ratios, and extraction manners were examined. Test results show that a cone-shaped subsidence region occurs around the suction caisson during the suction-assisted installation. The pullout bearing capacity of the suction caisson in sand is dominated by the loading rate and the loading manner. For the suction caisson subjected to monotonic loading, the maximum bearing capacity is reached at the pullout rate of about 20.0?mm/s. The mobilized vertical displacement corresponding to the pullout capacity increases with increasing the pullout rate. The passive suction beneath the suction caisson lid reaches the maximum value when the pullout bearing capacity is mobilized. In addition, during the suction caisson extracted by pumping water into the caisson, the maximum pore water pressure in the caisson is obtained under the displacement of approximately 0.04 times the caisson diameter. The absolute values of the maximum pore water pressures for the suction caissons approximately equal those of the maximum vertical resistances at the monotonic pullout rate of 5 mm/s. When the vertical displacements of the suction caissons with the aspect ratio of 1.0 and 2.0 reach 0.92 and 1.77 times the caisson diameter, respectively, the seepage failure occurs around the caissons. Using a scaling method, the test results can be used to predict the time length required for the prototype suction caisson to be extracted from the seabed.     

Assessment of soil factors controlling ephemeral gully erosion on agricultural fields

The soil factor is crucial in controlling and properly modeling the initiation and development of ephemeral gullies (EGs). Usually, EG initiation has been related to various soil properties (i.e. sealing, critical shear stress, moisture, texture, etc.); meanwhile, the total growth of each EG (erosion rate) has been linked with proper soil erodibility. But, despite the studies to determine the influence of soil erodibility on (ephemeral) gully erosion, a universal approach is still lacking. This is due to the complex relationship and interactions between soil properties and the erosive process. A feasible soil characterization of EG erosion prediction on a large scale should be based on simple, quick and inexpensive tests to perform. The objective of this study was to identify and assess the soil properties – easily and quickly to determine – which best reflect soil erodibility on EG erosion. Forty‐nine different physical–chemical soil properties that may participate in establishing soil erodibility were determined on agricultural soils affected by the formation of EGs in Spain and Italy. Experiments were conducted in the laboratory and in the field (in the vicinity of the erosion paths). Because of its importance in controlling EG erosion, five variables related to antecedent moisture prior to the event that generated the gullies and two properties related to landscape topography were obtained for each situation. The most relevant variables were detected using multivariate analysis. The results defined 13 key variables: water content before the initiation of EGs, organic matter content, cation exchange capacity, relative sealing index, two granulometric and organic matter indices, seal permeability, aggregates stability (three index), crust penetration resistance, shear strength and an erodibility index obtained from the Jet Test erosion apparatus. The latter is proposed as a useful technique to evaluate and predict soil loss caused by EG erosion. Copyright © 2018 John Wiley & Sons, Ltd.     

压缩感知技术在地震数据重建中的应用

地震资料室内处理过程要求野外采集的地震资料越多越好, 而地震数据远距离快速传输又要求野外地震数据量越少越好． 为解决这一矛盾, 将基于曲波变换与压缩感知的数据重建技术引入到地震资料处理中, 对实际的野外不完整数据进行压缩重建． 结果表明, 曲波变换相对于傅里叶变换在数据压缩采样方法中占有一定的优势． 但是, 在对实际资料进行处理时, 首先要对资料中的面波进行处理, 同时还要在一定曲波基元尺寸的情况下, 考虑缺失道数量的影响． 最终, 得到的重建数据图像纹理清晰、 连接自然, 从而验证了该方法的实用性和有效性．      

基于振动台试验的移动通信节点机房蓄电池组地震易损性分析

关键移动通信设备的地震易损性是城市移动通信系统地震灾害预测的基础。本文以移动通信系统节点机房中常用的蓄电池组作为研究对象,通过振动台试验来研究蓄电池组的抗震性能,并获得其地震易损性。试验过程中,首先采用FEMA P695建议的方法从美国PEER强震数据库中遴选出对蓄电池组较为危险的地震动记录作为试验激励,随后逐步增大各条地震动记录的幅值,基于振动台进行增量动力分析。试验后根据蓄电池组的地震损伤特征,定义了其损伤指标和损伤水平,并基于振动台试验数据分析获得了典型蓄电池组的地震易损性曲线。     

土-结构群相互作用体系地震响应振动台试验研究

设计并开展一系列土-结构群相互作用体系振动台试验,考虑结构数量、地震动类型与幅值等参数,研究土-结构群相互作用对结构及场地土响应的影响,并对模型土参数确定方法进行分析。研究结果表明,地表建筑物的存在并不总是减小自由场地面运动,但地面运动随着地表结构数量的增加而降低;土-结构群相互作用对位于结构群中心的结构响应影响最大,且会放大土体卓越频率附近的响应成分;不同评价指标之间具有不同的侧重点,但均可较好地评价结构群之间的相互作用;输入地震动的总能量越高,土-结构群相互作用越明显。     

基于时间序列的InSAR相干性量级估计

本文提出了一种适用于InSAR数据处理的自适应相干性量级估计方法,该方法能够满足复信号随机平稳的假设前提,并兼顾运算效率与估计精度.此方法生成的相干图具有很好的分布特征,避免了影像空间分辨率的损失.提出的算法分为两个步骤:(1)根据地物后向散射特性,对时间序列SAR影像进行聚类分析,选择具有同分布的样本,保证SAR影像质地平稳条件;(2)对干涉图进行条纹频率估计,采用极大似然(ML)条纹频率估计方法去除系统相位引起的复信号非平稳性,并根据Cramer-Rao边界条件改善条纹频率的估计精度.以美国南加州洛杉矶地区的ENVISAT ASAR数据集为例,本文将新方法与现有方法进行了量化分析.结果表明,较传统方法而言,基于时间序列的相干性估计方法能够得到更可靠、精度更高、空间特征更鲜明的干涉相干图.