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991.
In unsaturated soil modelling, collapse is viewed as an ordinary response, whereas swelling upon an increase of moisture is
considered as a special class of problems. However, an investigation based on fundamentals of plasticity indicates that the
two seemingly opposite responses are unified within the same ordinary elastoplasticity framework. In fact, similar to the
well-known contractive and dilative responses in the critical state framework, the collapsive and expansive responses of unsaturated
soils differ only in the sign of the dissipative hydrostatic stress. For a soil with a low applied net stress, the dissipative
mean normal stress during wetting is likely to be negative, and the plastic volumetric strain is kept negative (swelling)
as well, such that the dissipation is always positive, complying with the second law of thermodynamics. When the applied net
stress is high, the dissipative mean normal stress may turn to be positive, resulting in a positive plastic volumetric strain
(collapse). This paper explains the concept of this ‘ordinary’ modelling framework, and uses a bounding surface triaxial model
to demonstrate the concept. The numerical results are compared with experimental observations reported in the literature. 相似文献
992.
Formula of incipient velocity for flooded vehicles 总被引:3,自引:3,他引:0
With the climate change caused by global warming, the occurrence probability of urban flooding due to flash floods has increased
gradually. Flush floods propagate rapidly, which can lead to significant hazard to human life and property. Flood hazard to
vehicles has become more noticeable and frequent in recent years. Therefore, it is important to investigate the behaviour
of vehicles on flooded streets or roads. In the current study, a formula has been derived to predict the incipient velocity
of flooded vehicles according to the mechanical condition of sliding equilibrium. A series of flume experiments were conducted
using three types of scaled die-cast model vehicles, with two scales being tested for each type of vehicle. The experimental
data obtained for the small-scale model vehicles were used to determine the two parameters in the derived formula, and the
prediction accuracy of this formula was validated using the experimental data obtained for the large-scale model vehicles.
Finally, the corresponding incipient velocities under various incoming depths were computed using this formula for these three
prototype vehicles. It is found that for a specified vehicle, the value of incipient velocity reaches its minimum as the incoming
flow depth approaches the height of the vehicle, and the smaller and lighter vehicle like Mini Cooper is the easiest to start
sliding in floodwaters. The results can be used as a preliminary assessment to define the hazard to vehicles parking on flooded
streets or roads. 相似文献
993.
欧泊是一种具有特殊光学效应的宝石,其变幻莫测的色彩令人着迷。但在国内珠宝市场上欧泊的销售份额很小,有关其有效营销方法研究方面的参考资料基本处于空白状态。借助2010年上海世博会的契机,结合笔者在澳大利亚馆销售欧泊产品4个月的经历,着重从多角度吸引顾客、留住顾客、销售攻心术、灵活引导及创新推广活动等方面分析了澳大利亚AODC公司的营销策略,从中总结出几点建议,旨在对国内珠宝营销有所启发。 相似文献
994.
995.
996.
A 1.5-layer reduced-gravity model forced by wind stress is used to study the bifurcations of the North Equatorial Current(NEC).The authors found that after removing the Ekman drift,the modelled circulations can serve well as a proxy of the SODA circulations on the σθ=25.0 kg m~-3 potential density surface based on available long-term reanalysis wind stress data.The modelled results show that the location of the western boundary bifurcation of the NEC depends on both zonal averaged and local zero wind stress curl latitude.The effects of the anomalous wind stress curl added in different areas are also investigated and it is found that they can change the strength of the Mindanao Eddy(ME),and then influence the interior pathway. 相似文献
997.
998.
利用2008年夏季我国第3次北极科学考察资料,基于流式细胞技术,对白令海北部陆架区的微微型浮游植物丰度、细胞大小(碳含量)、色素浓度的分布特征进行了分析,并对该类群的环境适应性进行了研究。结果表明,微微型浮游植物中仅含聚球藻和真核藻,其丰度范围分别为0.14×106 2.69×106和0.23×106-12.49×106个/dm3。聚球藻的叶绿素a和藻红蛋白含量、微微型真核藻的叶绿素a含量与类群丰度以及微微型真核藻的类胡萝卜素含量与细胞大小间均存在同向变化趋势。两类藻偏向于喜温嗜淡型,更适合在寡营养环境中保持较高的丰度,但能在高营养盐浓度下形成相对较高的碳含量。越接近陆地,细胞越小,丰度越大,碳含量及FL2/FL3越低;所处层位越深、纬度越高,则细胞越大,碳含量及FL2/FL3越高。北极气温升高和径流量的增加有利于陆架区微微型浮游植物类群丰度的增加。 相似文献
999.
近年轴流转桨式机组水电站进水口事故闸门有两种布置方式,一门一机布置和多门一机布置.本文结合轴流转桨式机组特性,阐述防止机组飞逸的保护措施.然后通过两种布置方式的优缺点比较,建议采用一门一机的方式. 相似文献
1000.
随着城乡建设和市、区经济发展进程不断加快,莱芜市用地矛盾十分尖锐,仍然有粗放利用、破坏浪费土地资源的现象,特别是部分经营者圈而不用,造成土地的闲置浪费。总结了莱芜市国土资源局市区分局在节约集约用地方面取得的成效,分析了存在的问题,并提出了合理化建议。 相似文献