Laboratory Measurements of Vortex- and Wake-Induced Vibrations of A Tandem Arrangement of Two Flexible Risers     

刘怀增  王飞  蒋国盛  郭海燕  李效民 《海洋工程》2016,(1):47-56

The dynamic response of two flexible model risers in tandem arrangement immersed in a stepped current was analyzed. The risers, with an external diameter of 20 mm and a total length of 6200 mm, had an aspect ratio of 310. They were hinged to the support structure at the center-to-center distances away 3?12 times the external diameter. The top 1200 mm was exposed to a uniform current at a speed which was up to 0.9 m/s (the Reynolds number was 18000) and the rest in still water. The dynamic responses, which were obtained through the Fiber Bragg Grating strain gauges mounted on the surface, were analyzed by studying the cross-flow amplitudes and modal weights. The cross-flow vibration were observed up to the third mode, and the modal transformation from the second mode to the third mode was clearly observed. The experiment confirmed that the typical vortex-induced vibration (VIV) had occurred on the up-stream riser. But for the down-stream riser, the main excitation mechanism was wake-induced vibration (WIV). The modal transformation of WIV was more complex than that of VIV, which might be helpful for other researchers to study the interference effect.  相似文献   

土工袋垫层抗液化性能振动台试验研究     

刘斯宏  李博文  鲁洋  沈超敏  方斌昕  杭丹 《岩土力学》2022,43(Z2):183-192

土工袋能够有效地约束袋内土体,具有良好的滤水保土作用,可以用于地基抗液化,但土工袋抗液化性能尚未有系统及深入的研究。开展了一系列小振动台试验,验证土工袋垫层的抗液化效果,研究了振动加速度、土工袋层数和排列方式对抗液化性能的影响。结果表明：土工袋具有良好的抗液化效果,袋内土体的超静孔压比小于同深度处周围的土体;土工袋垫层的排水性能是在土工袋本身具有良好透水性的基础上,孔隙水会沿着土工袋与土体的界面以及袋间的空隙排出;相较于不透水刚性垫层,振动过程中土工袋垫层表面基本保持水平,发挥出较好的变形协调性;土工袋层数增加及交错式排列对抗液化效果有利。  相似文献   

软甲纲(节肢动物门:甲壳动物亚门)系统发育线粒体基因组研究     

申欣  田美  阎斌伦  朱嘉濠 《海洋学报(英文版)》2015,34(2):84-92

Along with the sequencing technology development and continual enthusiasm of researchers on the mitochondrial genomes, the number of metazoan mitochondrial genomes reported has a tremendous growth in the past decades. Phylomitogenomics—reconstruction of phylogenetic relationships based on mitochondrial genomic data—is now possible across large animal groups. Crustaceans in the class Malacostraca display a high diversity of body forms and include large number of ecologically and commercially important species. In this study, comprehensive and systematic analyses of the phylogenetic relationships within Malacostraca were conducted based on 86 mitochondrial genomes available from Gen Bank. Among 86 malacostracan mitochondrial genomes, 54 species have identical major gene arrangement(excluding t RNAs) to pancrustacean ground pattern,including six species from Stomatopoda, three species from Amphipoda, two krill, seven species from Dendrobranchiata(Decapoda), and 36 species from Pleocyemata(Decapoda). However, the other 32 mitochondrial genomes reported exhibit major gene rearrangements. Phylogenies based on Bayesian analyses of nucleotide sequences of the protein-coding genes produced a robust tree with 100% posterior probability at almost all nodes. The results indicate that Amphipoda and Isopoda cluster together(Edriophthalma)(BPP=100).Phylomitogenomic analyses strong support that Euphausiacea is nested within Decapoda, and closely related to Dendrobranchiata, which is also consistent with the evidence from developmental biology. Yet the taxonomic sampling of mitochondrial genome from Malacostraca is very biased to the order Decapoda, with no complete mitochondrial genomes reported from 11 of the 16 orders. Future researches on sequencing the mitochondrial genomes from a wide variety of malacostracans are necessary to further elucidate the phylogeny of this important group of animals. With the increase in mitochondrial genomes available, phylomitogenomics will emerge as an important component in the Tree of Life researches.  相似文献   

Variation of the Sectional Drag Coefficient of a Group of Buildings with Packing Density   总被引：2，自引：2，他引：0  

J. L. Santiago  O. Coceal  A. Martilli  S. E. Belcher 《Boundary-Layer Meteorology》2008,128(3):445-457

Reynolds-averaged Navier–Stokes (RANS) simulations of turbulent flow over groups of buildings with different packing densities are reported. The results for a selected packing density are compared with direct numerical simulations (DNS) previously validated against wind-tunnel data. The present study is focused on average properties of the flow, especially on the drag coefficients, and is a first attempt to provide information on these parameters (their values are not generally known) for a range of packing densities, for a given staggered arrangement of cubes using RANS methods. However, some of the limitations of RANS have come to light. Hence, it is recommended that such simulations are ‘calibrated’ against experimental or DNS data, as is done here.  相似文献   

软岩钻进用新型复合片钻头的研制与应用          下载免费PDF全文

杨春 《探矿工程》2010,37(12):74-76

为提高复合片在软岩钻进中的效率及寿命,提出了改变复合片切削齿形状,运用新的布齿方式和新的保径设计,设计制造的Φ76 mmPDC钻头在软岩钻进中取得了良好的效果。详细介绍了该软岩钻头的结构设计及现场应用效果。  相似文献   

隧洞工程弹性参数反演的可辨识性及量测优化布置探讨   总被引：1，自引：1，他引：0  

余远国  沈成武 《岩土力学》2010,31(11):3604-3612

探讨依据完备的量测信息开展弹性参数反演的可辨识性及量测的优化布置,对于指导岩土工程反演实践具有重要的实用价值。利用平面弹性复变函数方法和一般弹性理论,推导出任意形状隧洞的位移、应力解析表达式,基于隧洞围岩位移、应力的解析解,依据参数可辨识条件和量测优化布置的最灵敏原则,探讨了地下隧洞工程弹性反演参数的可辨识性及测点优化布置,并通过算例进行了验证。研究表明,依据完备的量测信息开展弹性反分析,只要测点布置方式适当、反演参数满足相应的限定条件,可同时惟一辨识出5个参数P、Q、M、E、μ。参数反演的可辨识性受隧洞形状复杂性的影响,随着隧洞复杂性的提高,参数可同时惟一辨识需满足的限制条件大为减少,对测点布置方式的要求也会降低。工程实践中,为避免量测数据的少量误差导致反演计算结果的大幅度波动,测点(线)应根据最灵敏原则优化选择各反演参数的灵敏系数最大的测点(线)组合进行量测布置。  相似文献   

尉氏县土地整理复垦开发规划     

余明全  陈常优 《地域研究与开发》1998,(Z1)

文章结合在尉氏县的实际工作,阐述了土地整理、复垦、开发的涵义、原则、目标和潜力;分析、制定了尉氏县土地整理、复垦、开发规划方案  相似文献   

论土地整理概念的科学界定   总被引：26，自引：3，他引：23  

姜爱林  姜志德 《地域研究与开发》1998,17(1):1-4

土地整理是土地利用的一种发展趋势,目前已成为社会关注的焦点。然而,从国内外的研究情况来看,土地整理的概念、内容都不尽一致。理论上的混乱无疑会给实际工作造成诸多的困扰。本文从分析比较国内外对土地整理的不同观念出发,并结合我国实际,科学地提出了土地整理的经济学概念及确定这一要概念必须遵循的规律。  相似文献   

HDTMA+柱撑离子空间几何尺寸与柱撑蒙脱石层间排列方式的研究   总被引：15，自引：6，他引：15  

朱建喜  何宏平  郭九皋  杨丹  谢先德 《矿物岩石》2003,23(4):1-4

用X射线衍射方法对不同柱撑浓度条件下制备的HDTMA^ 柱撑蒙脱石系列样品进行研究，结合有机离子的理论空间几何尺寸，提出有机柱撑离子在层间的不同排列展布方式。水平单层排列的HDTMA^ 离子可以有两种不同的排列方式并分别对应于柱撑产物的不同底面间距，水平双层排列虽然也可形成两种不同的排列方式，但是柱撑产物具有相同的底面间距，并用联锁嵌合结构解释了有机离子在水平双层和假三层排列模式下其实际总体高度要低于各单层高度数字之和。  相似文献   

沙尘暴问题的经济学分析     

李兴江  叶超 《地理与地理信息科学》2003,19(1):59-61

沙尘暴也是一个经济问题，引发沙尘暴的主要原因是人类不合理的经济活动，而其根本原因在于制度安排的不合理和低效率，该文从人口，博弈论，产品价格三方面进行了分析。  相似文献