近自由面非定常空化流动特征与稳定性机理研究

近自由面非定常空化流动是水面航行器提高航速的重要障碍,主要表现为自由面/空化区相互作用,影响空泡的非稳态特征,空化流动的兴波效应也值得关注。以往研究大多针对定常问题,非定常的算法及实验验证手段的报道很少。本研究建立了水/气/汽三相并包含空化相变效应的大涡模拟数值方法,基于小尺寸水下发射水箱完成了典型的验证实验。计算得到的非定常空泡形态演化与实验结果吻合良好,验证了计算方法的精度和可靠性。在此基础上,分析了空泡形态非稳态演化的特征与自由面/空化相互作用规律,讨论了自由面对空泡流动的约束效果和非稳态空泡的兴波效应。进一步改变不同的浸没深度,发现在航行体距离自由表面非常接近的情况下,会发生通气云状空泡和通气超空泡现象。在通气效应和回射流变薄两种因素的影响下,空泡在距离自由表面更近的条件下能够变得更稳定,自由面可能对空泡发展和稳定性产生整体的影响,值得未来进一步深入研究并探索工程应用的前景

横向来流内单孔气泡形成的理论与实验研究

水下气泡的运动是水下航行器减阻和化工领域中的基础问题。本研究针对横向来流条件下气泡形成的现象进行了研究,主要包括循环水槽实验和理论模型的建立与求解。首先用开有通气孔的平板模型在循环水槽中进行实验,并配合高速摄像设备记录气泡各时刻的形态。然后依据力平衡、运动学方程和量纲分析建立了气泡膨胀阶段和分离阶段的理论模型,利用四阶Runge-Kutta算法并结合初始条件进行数值求解,得到气泡在各个时刻的质心位置、倾斜角度和气泡尺寸大小。最后将数值计算结果与实验结果进行对比,结果表明两者具有良好的一致性,均方根误差为5.38%,进而证实了理论模型的可靠性

挡流条对轴对称航行体空化演化过程的影响研究

空泡的准周期性非稳态演化过程中,空泡的不断脱落和溃灭等会对航行体产生不利影响。本文讨论了一种在航行体前端附近设置挡流条来增加非稳态演化过程中空泡的稳定性的方式,并基于分离式霍普金森压杆发射实验研究了挡流条对空泡初生、发展、脱落及溃灭的全过程的影响。试验表明挡流条会改变空泡的演化过程,如使肩部空泡缩短,提前形成回射流,并在一定程度上增加非稳态演化过程中空泡的稳定性

Effects of open space on neighbourly social interaction : the case of Hong Kong

As a Global city, overall neighborly social interactions in Hong Kong are quite low. People living in community merely interact with each other and not sustain neighborliness. Social interactions in neighborhood level contribute the feelings of belonging and sense of community which are important factors to build up social capital. According to environment psychology, physical environment is a crucial mechanism to influence social interaction. Then open space as focal point of neighborhood environment may have important effects on neighborly social interaction. The goal of this dissertation is to examine the inter-connection of open space and social interaction and provide better open space planning strategies and design principles to boost neighborly social interaction. Firstly open space’s effect in social interaction is identified in theoretical framework. Then current open space planning and social interaction pattern of Hong Kong are reviewed in empirical background. Based on theoretical framework and empirical background, analysis of this study is launched with case studies of two public housing estate. The analysis is divided into two parts. First part is to confirm that open space with good quality could be act as catalyst to boost neighborly social interaction. Second part is to discover appropriate design of open space to stimulate social interaction. Then recommendations are provided, including strategies for establishing comprehensive open space planning and open space design guideline in terms of enhancing social interaction.published_or_final_versionUrban Planning and DesignMasterMaster of Science in Urban Plannin

毫米波MIMO系统中混合波束赋形算法

针对毫米波多输入多输出系统中的混合波束赋形问题,提出一种基于迭代更新思想的混合波束赋形算法,该算法通过提高模拟波束赋形矩阵与误差矩阵的相关性,获得了较优的系统性能。首先所提算法通过不断迭代更新得到误差矩阵,然后对误差矩阵进行奇异值分解得到左奇异值矩阵,并以此获得模拟波束赋形矢量,最后根据得到的模拟矢量更新模拟波束赋形矩阵。仿真结果表明,所提算法的性能优于传统的正交匹配追踪混合波束赋形算法,尤其当数据流数与射频链路数相等且数量较少时,所提算法的性能明显优于正交匹配追踪算法,且更近似于纯数字波束赋形的系统性能

Fair Value Manipulation to Avoid Loss and Earnings Decreases

【中文摘要】已有文献证明了上市公司在盈余管理动机下的公允价值操纵行为，在此基础上检验操纵公允价值盈余管理的结果表现和实现路径有助于丰富现有研究。以我国 2010~2016 年年报中披露公允价值分层信息的 A 股（A-Shares，人民币普通股票）非金融类上市公司为样本，研究发现：非金融类上市公司以公允价值计量的金融资产规模的扩张显著提升了公允价值操纵对盈余管理的影响程度，既有助于管理者达成盈余管理目标，同时又增大了管理者操纵公允价值的偏好程度；第一、第二层次公允价值均被作为操纵对象，管理者通过调节与第一层次公允价值相关的已实现损益和第二层次公允价值相关的未实现损益来实现规避亏损和盈余下滑的盈余管理目的。 【Abstract】Prior research shows that managers manipulate a firm's fair value informationso as to manage the firm’s earnings.We further studythe different practices that a firm uses to manipulate its fair value information in achieving its earnings management objectives.Using fair value hierarchy information disclosed by non-financial firms listed in the Chinese A-share market，we find that the expansion of fair-value-based financial assets of non-financial listed companies has significantly increased the role of fair value manipulation in earnings management. Specifically，the expansion of fair-value-based financial assets not only helps managers achieve their earnings management objectives，but also increases managers’ preference for manipulating the fair value of financial assets. We show that managers manipulate both levels 1 and 2 fair value in that they avoid lossesand declining earnings by adjusting realized gains and losses related to the level 1 fair value and byadjusting unrealized gains and losses related to the level 2 fair value.本文为2014 年度教育部人文社会科学研究一般项目“公允价值分层披露的经济后果研究”（14YJA630042）的阶段性成果