地下水动态预测的探讨   总被引：1，自引：1，他引：0       下载免费PDF全文

王光生  杨建青  于钋  杨桂莲 《水文》2013,33(3):25-28

简要介绍地下水数学模型的原理和应用实例,着重介绍在河北省大清河地下水系统的大沙河-磁河冲洪积扇孔隙地下水区,尝试建立地下水埋深变幅预测的统计相关方法和神经网络模型取得的良好效果;同时对地下水预测中的降水补给、边界和初始条件等的处理进行讨论,对数学模型和统计相关模型优缺点进行比较。  相似文献   

堆载条件下单桩负摩阻力模型试验研究   总被引：8，自引：2，他引：6  

杨庆  孔纲强  郑鹏一  栾茂田 《岩土力学》2008,29(10):2805-2810

通过对粉土中混凝土单桩竖向静载荷的模型试验,分析了在桩周土堆载条件下,端承桩、摩擦端承桩在桩周土含水率变化时,桩侧摩阻力、桩端阻力的变化规律及不同土层的沉降、“中性点”位置和下拽力的变化。研究发现,摩擦端承桩“中性点”位置随桩周土含水率、堆载等级的变化而变化,在最优含水率附近,土层的下陷量较大,致桩体沉降量也大,故“中性点”的位置会有所上升;随着桩周土堆载的增大,桩周土对桩侧的下拽力也增大,桩体进一步下陷,使桩土相对位移反而减少,“中性点”有所上升。  相似文献   

负摩擦作用下PCC桩沉降计算   总被引：3，自引：0，他引：3  

刘汉龙  张晓健 《岩土力学》2007,28(7):1483-1486

从桩-土相互作用的机制出发,建立了均质地基中PCC桩负摩阻力传递的弹性微分方程。提出了基于有限差分法的一种桩身位移的迭代算法,计算结果表明,该计算方法收敛性好,且符合实际情况。根据中性点定义得出其位置在桩身中下部,与以往的研究结果相吻合。结果还表明,PCC桩比等截面的实心桩有较小的沉降。  相似文献   

不稳定边界层下地形重力内波   总被引：3，自引：0，他引：3  

刘辉志  张伯寅  桑建国  洪钟祥  胡非 《大气科学》2000,24(4):509-518

水槽实验及线性理论研究表明,当低层大气处于近中性或不稳定时,如果地形引起的动力扰动足够强,地形扰动可在上部稳定层结中激发出重力内波,波动反过来影响低层流场,引起动量输送。低层大气处于近中性或不稳定时,地形波同样对大气运动可产生波阻,这应引起模式工作者的重视。最后讨论了大气粘性对中性或不稳定层结下地形波的影响。  相似文献   

Comparison of scenario‐neutral approaches for estimation of climate change impacts on flood characteristics     

Luise Keller  Ole Rssler  Olivia Martius  Rolf Weingartner 《水文研究》2019,33(4):535-550

Scenario‐neutral assessments of climate change impact on floods analyse the sensitivity of a catchment to a range of changes in selected meteorological variables such as temperature and precipitation. The key challenges of the approach are the choice of the meteorological variables and statistics thereof and how to generate time series representing altered climatologies of the selected variables. Different methods have been proposed to achieve this, and it remains unclear if and to which extent they result in comparable flood change projections. Here, we compare projections of annual maximum floods (AMFs) derived from three different scenario‐neutral methods for a prealpine study catchment. The methods chosen use different types of meteorological data, namely, observations, regional climate model output, and weather generator data. The different time series account for projected changes in the seasonality of temperature and precipitation, in the occurrence statistics of precipitation, and of daily precipitation extremes. Resulting change in mean AMF peak magnitudes and volumes differs in sign between the methods (range of ?6% to +7% for flood peak magnitudes and ?11% to +14% for flood volumes). Moreover, variability of projected peak magnitudes and flood volumes depends on method with one approach leading to a generally larger spread. The differences between the methods vary depending on whether peak magnitudes or flood volumes are considered and different relationships between peak magnitude and volume change result. These findings can be linked to differing flood regime changes among the three approaches. The study highlights that considering selected aspects of climate change only when performing scenario‐neutral studies may lead to differing representations of flood generating processes by the approaches and thus different quantifications of flood change. As each method comes with its own strengths and weaknesses, it is recommended to combine several scenario‐neutral approaches to obtain more robust results.  相似文献   

Selection of scale can reverse the importance of stochastic controls on community assembly     

Daehyun Kim 《自然地理学》2019,40(2):111-126

Reconciling the long-standing debate on the importance of niche-related and neutral factors on community assembly, recent research suggests that both deterministic and stochastic processes operate simultaneously along a continuum in many biogeographical systems. In particular, stochastic processes seem to lose importance under stressful conditions, which results in the increasing influence of deterministic counterparts. In this paper, I show that, at local scales, this stochasticity–stress relationship can be reversed along the environmental stress gradients within a salt marsh: stochasticity manifested under harshness. Here, low-lying, more stressful sites contained all of the plant species of the local pool (i.e. a greater chance of ecological drift), whereas high-elevation, less stressful sites exhibited reduced species richness due to competitive exclusion (i.e. a lower chance of ecological drift). I conclude that determining whether the importance of stochasticity in shaping community structure is greater under benign or harsh conditions depends on the scale of interest.  相似文献   

Review of Global Ocean Intermediate Water Masses: 1.Part A, the Neutral Density Surface (the ‘McDougall Surface’) as a Study Frame for Water-Mass Analysis     

Yuzhu You )  )  * ) The University of Sydney Institute of Marine Science 《中国海洋大学学报(英文版)》2006,(3)

1Preface Todescribeoceanicintermediatewatermasses,itis necessarytohaveawell definedstudyframeorsurfacebecauseofthefluctuationnatureofintermediatewa ters.Itiswellunderstoodthatoceanicwater mass mixingdoesnotalignwitheitheraconstantgeopoten tialdepthorapropertysurfacesuchastemperature,salinity,pressureanddensitysurfacesbutfollowsa neutraldensitysurface.Thisisbecauseawaterparcelmovesasmalldistanceisentropicallyandadiabaticallyontheneutraldensitysurfacewithoutdoingworka gainstabuoyantrestoringforc…  相似文献   

中立型随机发展系统的适定性     

徐道义 《南京气象学院学报》2017,9(4):400-405

针对中立型随机发展系统的温和解与轨道温和解,给出了其存在唯一性与渐近估计的充分条件,推广了经典的Pazy定理与一些近期文献的主要工作.  相似文献   

Age determination of Baltic herring from whole otoliths and from neutral red stained otolith cross sections   总被引：2，自引：1，他引：2  

Peltonen  Heikki; Raitaniemi  Jari; Parmanne  Raimo; Eklund  Jan; Nyberg  Kari; Halling  Folke 《ICES Journal of Marine Science》2002,59(2):323-332

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二阶亚线性中立型微分方程解的振动性     

姜福德 《中国海洋大学学报(自然科学版)》1995,(3)

本文在证明了二阶亚线性中立型微分方程的非振动解满足的基础上，给出了所有解振动的某些充分条件。  相似文献