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371.
An experimental investigation was conducted on a flexible riser with and without various strake arrangements. The aim of the present work was to further improve the understanding of the response performance of the vortex-induced vibration (VIV) of a riser with helical strakes. Two current profiles, including uniform and linearly sheared flows, were simulated. The uniform current was simulated by towing the riser model in one direction using the towing carriage, and the linearly sheared current was simulated by fixing one end of the riser and using a driven cantilever to traverse a circular arc. Based on the modal superposition method, the displacement responses were obtained from the measured strain. Strakes with different heights and pitches were analysed, and response parameters such as the displacement response and fatigue damage were studied. The results of the bare model test show that the lock-in phenomenon displays multi-order characteristics, and the VIV displacement decreases with an increased order of the lock-in regime. The results of the straked model test indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the response performance depends closely on the geometry of the strake configuration. 相似文献
372.
Experimental Study on Response Performance of VIV of A Flexible Riser
with Helical Strakes 总被引:1,自引:1,他引:0
Laboratory tests were conducted on a flexible riser with and without helical strakes. The aim of the present work is to further understand the response performance of the vortex induced vibration (VIV) for a riser with helical strakes. The experiment was accomplished in the towing tank and the relative current was simulated by towing a flexible riser in one direction. Based on the modal analysis method, the displacement responses can be obtained by the measured strain. The strakes with different heights are analyzed here, and the response parameters like strain response and displacement response are studied. The experimental results show that the in-line (IL) response is as important as the cross-flow (CF) response, however, many industrial analysis methods usually ignore the IL response due to VIV. The results also indicate that the response characteristics of a bare riser can be quite distinct from that of a riser with helical strakes, and the response performance depends on the geometry on the helical strakes closely. The fatigue damage is further discussed and the results show that the fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. 相似文献
373.
通过研究深冲铀矿区γ能谱铀异常、氡浓度异常特征和激电异常特征,探索矿区范围岩体、断裂构造和蚀变带与物化探信息显示特征的关系。据此,结合矿区地质特征,总结物化探方法应用效果,矿致异常综合特征。 相似文献
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376.
为建立一种简易的FLAC3D建模方法,降低FLAC3D前处理时的建模难度,本文基于Python编程语言开发了建模文件生成程序。该程序以岩体各层位的高程信息为基础,采用Kriging插值生成离散网格点数据;并采用离散网格点自动生成建模所需要的网格数据文件;将该文件导入FLAC3D软件中,即可生成与真实钻孔数据和地层信息吻合的三维模型。程序提供了3种FLAC3D内置单元模型可供选择。该方法采用Kriging插值算法,可生成精确的三维地层模型数据。与FLAC3D软件自身的脚本建模语言相比,该方法简单快速。本文使用3类应用数据进行建模,验证提出的插值建模方法可以针对复杂的地形和地质信息生成精确的三维模型。研究成果为采用FLAC3D进行复杂地质区域数值模拟计算提供了一种简单、高效、准确的建模工具。 相似文献
377.
面向露天矿山生产对于矿车装载量核算的需求,本文提出了一种利用单线激光雷达扫描的矿车装载量自动核算方法。该方法首先采用固定式单线激光雷达对目标车辆进行俯视扫描,基于车辆形态特征分割出载荷物顶部点云;然后经时态校正,并与预先构建的车辆信息数据库进行匹配,重建出载荷物的三维表面模型;最后通过对载荷物表面模型的切片积分实现方量核算。以齐大山铁矿运输为例,对多台矿车装载量进行核算测试。结果表明,本文方法可在车辆正常行驶的情况下实时获取载荷物的表面三维点云,平均建模误差为2.54 cm,装载方量核算误差为1.17%。 相似文献
378.
At the current rate of global warming, the target of limiting it within 2 degrees by the end of the century seems more and more unrealistic. Policymakers, businesses and organizations leading international negotiations urge the scientific community to provide realistic and accurate assessments of the possible consequences of so called “high end” climate scenarios.This study illustrates a novel procedure to assess the future flood risk in Europe under high levels of warming. It combines ensemble projections of extreme streamflow for the current century based on EURO-CORDEX RCP 8.5 climate scenarios with recent advances in European flood hazard mapping. Further novelties include a threshold-based evaluation of extreme event magnitude and frequency, an alternative method to removing bias in climate projections, the latest pan-European exposure maps, and an improved flood vulnerability estimation.Estimates of population affected and direct flood damages indicate that by the end of the century the socio-economic impact of river floods in Europe is projected to increase by an average 220% due to climate change only. When coherent socio-economic development pathways are included in the assessment, central estimates of population annually affected by floods range between 500,000 and 640,000 in 2050, and between 540,000 and 950,000 in 2080, as compared to 216,000 in the current climate. A larger range is foreseen in the annual flood damage, currently of 5.3 B€, which is projected to rise at 20–40 B€ in 2050 and 30–100 B€ in 2080, depending on the future economic growth. 相似文献
379.
采用室内暴露试验方法,以单细胞凝胶电泳技术(SCGE)检测,研究了Cu、Pb不同浓度梯度与不同暴露时间联合染毒对泥鳅卵细胞DNA的损伤.结果表明,各Cu、Pb浓度组DNA平均迁移长度增加,与阴性对照组比较差异有显著性(P<0.05).此外,随着Cu、Pb染毒剂量的增加,各试验组DNA的平均迁移长度逐渐增加,在试验浓度梯度范围内(Cu 0.01mg/L+Pb 0.05mg/L、Cu 0.10mg/L+Pb 0.50mg/L、Cu 0.25mg/L+Pb 0.75mg/L),存在较为显著的剂量-效应关系(P<0.05),但未见明显的时间-效应关系(P>0.05).Cu、Pb可引起泥鳅卵细胞凋亡和DNA损伤,卵细胞的不同损伤水平可望作为较为理想的水环境基因毒性指标. 相似文献
380.
Saving lives in earthquakes: successes and failures in seismic protection since 1960 总被引:1,自引:1,他引:0
Robin Spence 《Bulletin of Earthquake Engineering》2007,5(2):139-251
This paper will look at what we have and have not achieved in reducing the risks to human life from earthquakes in the last
50 years. It will review how success has been achieved in a few parts of the world, and consider what needs to be done by
the scientific and engineering community globally to assist in the future task of bringing earthquake risks under control.
The first part of the talk will re-examine what we know about the casualties from earthquakes in the last 50 years. Almost
80% of about 1 million deaths turn out to have been caused by just ten great earthquakes, together affecting a tiny proportion
of the territory at risk from heavy ground shaking. The disparity between richer and poorer countries is also evident, not
only in fatality rates, but also in their rates of change. But the existing casualty database turns out to be a very poor
basis for observing such differences, not only because of the small number of lethal events, but also because of the very
limited data on causes of death, types and causes of injury. These have been examined in detail in only a few, recent events.
All that can be said with certainty is that a few wealthier earthquake-prone countries or regions have made impressive progress
in reducing the risk of death from earthquakes, while most of the rest of the world has achieved comparatively little, and
in some areas the problem has become much worse. The second part of the paper looks in more detail at what has been achieved
country-by-country. Based on a new expert-group survey of key individuals involved in earthquake risk mitigation, it will
examine what are perceived to be the successes and failures of risk mitigation in each country or group of countries. This
survey will be used to highlight the achievements of those countries which have successfully tackled their earthquake risk;
it will examine the processes of earthquake risk mitigation, from campaigning to retrofitting, and it will consider to what
extent the achievement is the result of affluence, scientific and technical activity, political advocacy, public awareness,
or the experience of destructive events. It will ask to what extent the approaches pioneered by the global leaders can be
adopted by the rest. The final section of the talk will argue that it can be useful to view earthquake protection activity
as a public health matter to be advanced in a manner similar to globally successful disease-control measures: it will be argued
that the key components of such programmes—building in protection; harnessing new technology and creating a safety culture—must
be the key components of earthquake protection strategies also. It will consider the contribution which the scientific and
engineering community can make to bringing down today’s unacceptably high global earthquake risk. It will be suggested that
this role is wider than commonly understood and needs to include:
Building-in protection
Harnessing new technologies
Creating a safety culture
Examples of some of these actions will be given. International collaboration is essential to ensure that the resources and
expertise available in the richer countries is shared with those most in need of help. And perhaps the most important single
task for the engineering community is work to counter the widespread fatalistic attitude that future earthquakes are bound
to be at least as destructive as those of the past. 相似文献
• | Improving and simplifying information available for designers and self-builders of homes and infrastructure. |
• | Devising and running “building for safety” programmes to support local builders. |
• | Developing and testing cost-effective techniques for new construction and retrofit. |
• | Involvement in raising public awareness. |
• | Political advocacy to support new legislation and other actions. |
• | Prioritising action on public buildings, especially schools and hospitals. |