排序方式： 共有52条查询结果，搜索用时 31 毫秒
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海上自升式钻井平台以其造价低廉、便于移动和安装的优势被广泛应用于海洋地质勘察、风电安装和油气开采等领域,其基础类型多为桩靴基础。为了保证平台能在恶劣的海洋环境中安全作业,桩靴基础需要贯入海床以下一定深度以获得足够的承载力。然而,当桩靴基础在上硬下软土层中贯入时可能发生穿刺破坏导致平台损坏甚至倾覆。已有的桩靴穿刺破坏分析方法基于预设的地层参数预测穿刺荷载,由于无法考虑海床中地层及土性的不确定性,其准确性有待提高。将桩靴基础贯入过程中的监测数据与穿刺破坏机理相结合,通过66组离心机模型试验结果表征土体不确定性的影响,发展贝叶斯预测模型,实现了峰值阻力和穿刺深度的实时预测。基于规范推荐的荷载扩展分析法和冲剪系数分析法,建立了适用于规范法的概率模型,采用该模型对上砂下黏土层中桩靴基础的穿刺行为进行了预测,结果表明所提方法的预测精度随着监测数据的增加而提高,预测得到的峰值阻力误差在10%以内。 相似文献
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美意味着和谐,这一观点早在两千年前就有希腊哲学家提出来了.后来的艺术家、美学家和作家们就一直在诠释着这一思想.英国著名女作家简·奥斯汀就是其中的代表人物之一,她的小说中极为明显地体现了和谐之美.从几个方面论述了简·奥斯汀的这一写作特色. 相似文献
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A. Van Ardenne P. N. Wilkinson P. D. Patel J. G. Bij De Vaate 《Experimental Astronomy》2004,17(1-3):65-77
ASTRON has demonstrated the capabilities of a 4 m2, dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept”, EMBRACE, which will have an area of 625 m2, operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams. With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator. 相似文献
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Benjamin L. Branoff 《水文科学杂志》2020,65(8):1326-1343
ABSTRACT In this study, water level models are constructed to characterize mangrove flooding across urban gradients in Puerto Rico. The most urban sites exhibited 95% longer hydroperiods, 23% lower flood frequencies, and 110% lower depths than the least urban sites. Rainfall importance was explained more by geomorphology and tidal connectivity than by urbanization, but there was evidence for changes in tidal amplitudes along the urban gradient. Relationships between surface water chemical metrics and land cover contradicted previous studies by suggesting lower nutrients and biochemical oxygen demand with increasing urbanization. However, much of this changed with the exclusion of potential outlier sites, as well as under different statistical comparisons. These results reinforce the understanding that the most important drivers of urban mangrove hydrology and water quality in Puerto Rico are likely geomorphology and tidal connectivity, with some influence from surrounding land cover. Results should be considered alongside the reported errors stemming from digital elevation and rainfall response models. 相似文献
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为拓展养殖空间,发展开放海区鲍养殖产业,在福建兴化湾新开发海区进行了抗风浪养鲍新技术的研究,对开放海区与传统遮蔽养殖海区、延绳式PVC管养技术与传统筏架式筐养技术进行了分析比较.结果表明,经19个月的养殖,开放海区PVC管养组鲍的日均增质量以及成活率分别为(106.41±5.33)mg/d和82.75％,显著大于处在开放海区和遮蔽海区的2个筐养组(P＜0.05).冬春季为鲍的最佳生长时期,其日均增长表现为PVC管养组大于筐养组(P＜0.05);开放海区大于传统遮蔽养殖海区(P＜0.05).养殖器具的污损生物附着量则表现为所有筐养组均显著大于PVC管养组(P＜0.05).夏秋季采用水下延绳式PVC管养模式还能有效地避免高温、污损生物和台风的侵袭与危害. 相似文献
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Francis Kamau Muthoni Frederick Baijukya Mateete Bekunda Haroon Sseguya Anthony Kimaro Tunrayo Alabi 《国际地球制图》2019,34(4):368-390
This paper generates an extrapolation suitability index (ESI) to guide scaling-out of improved maize varieties and inorganic fertilizers. The best-bet technology packages were selected based on yield gap data from trial sites in Tanzania. A modified extrapolation detection algorithm was used to generate maps on two types of dissimilarities between environmental conditions at the reference sites and the outlying projection domain. The two dissimilarity maps were intersected to generate ESI. Accounting for correlation structure among covariates improved estimate of risk of extrapolating technologies. The covariate that highly limited the suitability of specific technology package in each pixel was identified. The impact based spatial targeting index (IBSTI) identified zones that should be prioritized to maximize the potential impacts of scaling-out technology packages. The proposed indices will guide extension agencies in targeting technology packages to suitable environments with high potential impact to increase probability of adoption and reduce risk of failure. 相似文献
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Eakta Jain Susan K. Jacobson Pallavi Raiturkar Nia A. Morales Archana Nagarajan Beida Chen 《社会与自然资源》2019,32(10):1092-1098
AbstractWe used heart rate change as a tool to study how positive and negative wildlife conservation messaging impacts a viewer, and which types of animal images stimulate greatest reaction. We used scenes from five wildlife conservation videos available from environmental organization websites and YouTube, with positive and negative messaging. We found both very positive and very negative messaging in videos may be similarly effective in engaging viewers. A trend in greater changes in heart rate when insects, mammals, and birds appear on the screen suggests generally high human interest in these taxa, potentially due to avoidance and attraction responses. The number of scenes (N?=?54) in which various taxa appear reflects bias toward mammals (65%) and birds (17%) to capture viewers’ attention. Arousal is a primary step in engaging an audience to attend to a message. Physiological research offers innovative new techniques to evaluate public responses to communications about biodiversity conservation. 相似文献
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复杂土层中自升式平台桩靴安装穿刺预测 总被引：1，自引：1，他引：0
由于复杂海洋工程地质条件的普遍性,自升式平台在安装过程中穿刺事故频发,近年来涌现出大量针对自升式平台桩靴基础在复杂土层中穿刺预测方法的研究。为了方便工程设计人员的理解和使用,首先简单介绍这些研究中所采用的技术手段,总结现行规范ISO 19905-1建议的桩靴在复杂土层中贯入阻力的预测方法以及最新文献中提出的新的设计方法,并对规范方法和新方法的优缺点进行了评价。所总结的设计方法针对国内外常见的含穿刺风险的海洋地基形式,包括双层"砂—黏"、三层"硬—软—硬"黏性土、三层"软—硬—软"黏性土、三层"黏—砂—黏"地层以及四层"黏—砂—黏—硬层土"地层。通过对离心机模型试验的预测,对规范方法和新方法的预测精度进行了比较,对比结果显示新方法对桩靴穿刺破坏的预测更为合理精确。 相似文献
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在海洋工程中,移动钻井平台在作业结束后需要转场时,经常会遇到拔桩困难的问题,桩靴底部的吸附力是上拔力的重要组成部分,明确其产生机理及发展规律对于上拔力计算与缓解上拔困难问题有重要意义。通过室内模型试验研究了黏土中桩靴底部真空度对桩靴吸附力产生机理的影响,试验结果表明,桩靴底部真空度的变化对上拔力的影响显著,而桩靴贯入深度和上拔速率会对真空度产生影响。当真空度达到峰值时,桩靴底部吸附力与上拔力几乎同时达到峰值,因此可以通过减小桩靴底部真空度的措施来减小上拔力。根据试验结果,提出了运用真空吸盘理论来计算桩靴底部吸附力的计算公式。所述吸附力计算方法与试验结果进行对比,其误差较小,对工程实践具有一定的参考意义。 相似文献