Extended Impact of Cold Air Invasions in East Asia in Response to a Warm South China Sea and Philippine Sea

During boreal winter,the invasion of cold air can lead to remarkable temperature drops in East Asia which can result in serious socioeconomic impacts.Here,we find that the intensity of strong synoptic cold days in the East China Sea and Indochina Peninsula are increasing.The enhanced synoptic cold days in these two regions are attributed to surface warming over the South China Sea and Philippine Sea(SCSPS).The oceanic forcing of the SCSPS on the synoptic cold days in the two regions is verified by numerical simulation.The warming of the SCSPS enhances the baroclinicity,which intensifies meridional wind and cold advection on synoptic timescales.This leads to a more extended region that is subject to the influence of cold invasion.

Surface settlements induced by twin tunneling in silty sand

Surface settlements caused by twin tunneling are a major interest in underground space engineering.Most prevailing studies have investigated the surface settlements observed over twin tunnels constructed in clay.Yet,less attention is given to the twin tunnels exca-vated in silty sand,which is the focus of this study.A comprehensive field monitoring scheme was designed in the Hangzhou metro line six project to measure the surface settlements during twin tunneling by adopting earth pressure balance shields.The influence of four shield operational parameters,namely,face pressure,tail grouting pressure,penetration rate,and pitching angle on the surface settle-ments due to twin tunneling are explored.In general,the total settlement profiles observed over twin tunnels follow an inverted bimodal shape.The post-settlement observed over the 1^(st)tunnel due to the 2^(nd)tunnel excavation is non-trivial when the twin tunnels are spaced closely.Low face pressure and tail grouting pressure can induce excessive peak surface settlements during twin tunneling in silty sand.

可压缩壁湍流物理与建模研究进展

对高速边界层转捩与湍流的理解、建模与控制不但具有广泛的学术兴趣,而且对高速飞行器的设计与节能有至关重要的意义,因为转捩和湍流会急剧增加壁面摩阻和热流.根据Morkovin假设,高速流动具有一些与不可压缩流动本质上相似的特征,但另一方面,由于存在热力学过程、激波、高焓效应等多物理场耦合,与不可压缩流动也有显著区别.本文综述了高速边界层转捩与湍流的物理和建模方面的最新研究进展,其中较大部分内容为湍流研究.为了物理过程描述的完整性,我们首先简要综述了高速流动转捩,主要关注气动加热原理和推迟转捩的被动控制策略.随后,我们总结了近期在湍流平均流向速度和温度的标度率方面的一些令人鼓舞的发现,这些标度率能够用于构建一系列新颖的壁面模型以提高模式精度.此外,作为湍流建模的基础之一,我们还总结了湍流结构方面的研究,尤其关注边界层对数区含能运动的标度率与建模.另外,我们综述了各种用于预测壁湍流的线性模型.尽管湍流通常被认为是高度非线性的,这些线性模型在过去二十年的研究中取得了较大的成功.最后,我们对综述进行总结,并简要展望未来研究.