一种计算补偿最小二乘正则化参数的最优化方法     

丁士俊  朱留洋  姜卫平 《大地测量与地球动力学》2015,35(1):115-117

在半参数模型补偿最小二乘估计中,如何有效地计算正则化参数是求解的关键。在建立一种新的补偿最小二乘模型的基础上,基于广义交叉核实与L曲线准则,采用最优化方法计算正则化参数。仿真计算表明,本文方法是一种计算正则化参数更为有效的方法。  相似文献   

近水平厚层高陡斜坡崩塌机制研究     

冯振  李滨  贺凯 《地质力学学报》2014,20(2):123-131

近水平厚层高陡斜坡岩层倾角小于10°,具有软硬相间或上硬下软的结构,常形成高陡斜坡或陡崖地形,主要以大型崩塌的形式发生破坏。在梳理国内外文献的基础上,从岩体破坏机制出发,对近水平厚层高陡斜坡崩塌的形成过程、破坏机制、失稳模式进行分析,总结归纳了6种地质力学模型,包括滑移-拉裂、塑流-拉裂、倾倒-拉裂、剪切-错断、剪切-滑移、劈裂-溃屈,并提出了相应的野外识别特征。   相似文献   

Effect of cross‐section interpolated bathymetry on 2D hydrodynamic model results in a large river          下载免费PDF全文

Jeff T. Conner  Daniele Tonina 《地球表面变化过程与地形》2014,39(4):463-475

Two‐dimensional (2D) hydrodynamic models have been increasingly used to quantify aquatic habitat and stream processes, such as sediment transport, streambed morphological evolution, and inundation extents. Because river topography has a strong influence on predicted hydraulic conditions, 2D models require accurate and detailed bathymetric data of the stream channel and surrounding floodplains. Besides collection of mass points to construct high‐resolution three‐dimensional surfaces, bathymetries may be interpolated from cross‐sections. However, limited information is available on the effects of cross‐section spacing and the derived interpolated bathymetry on 2D model results in large river systems. Here, we investigated the effects of cross‐section spacing on flow properties simulated with 2D modeling at low, medium and high discharges in two morphologically different reaches, a simple (almost featureless with low sinuosity) and a complex (presenting pools, riffles, runs, contractions and expansions) reach of the Snake River (Idaho, USA), the tenth largest river in the United States in terms of drainage area. We compared the results from 2D models developed with complete channel bathymetry acquired with multibeam sonar data and photogrammetry, with 2D model results that were developed using interpolated topography from uniformly distributed transects. Results indicate that cross‐sections spaced equal to or greater than 2 times the average channel width (W*) smooths the bathymetry and suppresses flow structures. Conversely, models generated with cross‐sections spaced at 0.5 and 1 W* have stream flow properties, sediment mobility and spatial habitat distribution similar to those of the complete bathymetry. Furthermore, differences in flow properties between interpolated and complete topography models generally increase with discharge and with channel complexity. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Links between wave forcing,offshore islands and a macro‐tidal headland‐bound bay beach          下载免费PDF全文

Tony Thomas  Michael R. Phillips  Allan T. Williams  Rhian E. Jenkins 《地球表面变化过程与地形》2014,39(2):143-155

Profiles were analysed in conjunction with wave climate to assess offshore island influences on an embayed beach at Tenby, Wales. Time series analyses showed medium and short‐term beach oscillation, with volume exchanges between zones lagging by up to six months. Dominant southerly and southwesterly waves caused sub and low tidal longshore drift from south towards north, while less frequent southeasterly waves generated counter drift. Modelled inshore breaking waves had less energy than offshore ones and the former behaved differently between the low and high tidal zones (spring tidal range of 7 · 5 m). Variations in wave direction from directly behind the islands resulted in reduced wave heights and statistical analyses agreed with wave model results. These were correlated to morphological change and it was concluded that offshore islands change wave dynamics and modify the morphology of embayed beaches in their lee. Consequently, this work provides significant new insights into offshore island influences, shoreline behaviour and especially tidal setting Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

在线监测环境下土木结构的模态识别研究   总被引：4，自引：0，他引：4  

淡丹辉  孙利民 《地震工程与工程振动》2004,24(3):82-88

建立在线监测环境下结构考虑时效的模态识别计算方案。采用基于各测点加速度响应互功率谱的频域多参考点模态识别法来实现结构模态参数的抽取,从而绕过了监测环境下激励监测的技术难题;并用频域的平均法使识别参数的拟合曲线平滑和发现参数的变化趋势。通过对美国结构健康监测研究小组公布的Benchmark问题的第一阶段解析模型模拟加速度响应数据的识别,表明本文采用的算法有较好的识别精度和识别速度,是一个可行的在线监测环境下的模态识别计算方案。  相似文献   

河南省桐柏县银洞坡金矿床地质地球化学特征   总被引：9，自引：3，他引：6  

简新玲 《地质与勘探》2004,40(2):41-45

银洞坡金矿是我国重要的变质碎屑岩型金矿之一,为丰富此类矿床的研究内容和服务领域,时该类型金矿成矿条件及地球化学特征的总结,具有重要意义.在时成矿地质背景,地球化学参数及地球化学异常特征分析研究的基础上,建立了地球化学找矿标志,以期为该类型金矿的普查评价起到借鉴作用.  相似文献   

Turbulent flow structures in alluvial channels with curved cross‐sections under conditions of downward seepage          下载免费PDF全文

Vishal Deshpande  Bimlesh Kumar 《地球表面变化过程与地形》2016,41(8):1073-1087

Experimental investigations have been done to analyze turbulent structures in curved sand bed channels with and without seepage. Measures of turbulent statistics such as time‐averaged near‐bed velocities, Reynolds stresses, thickness of roughness sublayer and shear velocities were found to increase with application of downward seepage. Turbulent kinetic energy and Reynolds normal stresses are increased in the streamwise direction under the action of downward seepage, causing bed particles to move rapidly. Analysis of bursting events shows that the relative contributions of all events (ejections, sweeps and interactions) increase throughout the boundary layer, and the thickness of the zone of dominance of sweep events, which are responsible for the bed material movement, increases in the case of downward seepage. The increased sediment transport rate due to downward seepage deforms the cross‐sectional geometry of the channel made of erodible boundaries, which is caused by an increase in flow turbulence and an associated decrease in turbulent kinetic energy dissipation and turbulent diffusion.  相似文献   

X射线断层扫描投影图像背景不一致的校准          下载免费PDF全文

白娟娟  杨玉双  王海鹏 《CT理论与应用研究》2016,25(6):661-670

在X射线断层扫描(X-ray CT)成像过程中,经常会出现射线源、样品和探测器三者之间的相对移动,导致采集的投影图像(Projection image)以及亮场图像(flat field image)的空间位置配准关系出现偏差。这直接影响了投影图像背景的正常扣除,以及后续的CT图像重建。本文利用互相关方法,求出各投影图像背景与探测器原始采集位置之间的不一致量。然后将投影图像和亮场图像作相应变换,最后扣除背景得到校准后的图像。由于该方法对图像灰度较为敏感,所以在对实际样品校准之前,本文先对该样品投影图像及亮场图像进行了照度归一化。实验结果表明,该方法能够有效校正由射线源、样品和探测器之间相对移动造成的CT投影图像背景不一致,获得较好的CT投影图像和重建切片。   相似文献   

层状含水页岩的抗拉强度特性试验研究     

腾俊洋  唐建新  张闯 《岩土力学》2018,39(4):1317-1326

为分析层理和水对页岩的抗拉强度特性的影响,现场选取龙马溪组黑色页岩制备成4种含水状态含层理页岩,沿与层理呈0°、30°、60°和90°夹角加载进行巴西劈裂圆盘试验,试验过程同步进行声发射测试,并采用离散元软件3DEC对试验结果进行数值模拟验证。结果表明,相比于含层理页岩,同时考虑含水和层理的页岩在巴西劈裂试验中有其独特的破坏模式和力学特性。含层理页岩的巴西劈裂破坏模式和抗拉强度均与层理角度和含水率有关,破坏模式主要受控于层理与荷载的加载方向,水虽不会影响其破坏模式但能够导致次生裂纹的形成。抗拉强度则表现出随层理角度的增加而先减小后增大,随含水率的增加而减小的趋势。并且,在页岩同时受水和层理损伤作用时,受层理损伤程度越大,水对其损伤程度也越高。通过对含层理不同含水率页岩的微观结构分析得到了上述变化规律的内在机制,即页岩层理面处的内部矿物颗粒遇水膨胀,产生膨胀力作用,使页岩内部结构变得松散、破碎,微裂纹逐渐增多、变宽,宏观表现为次生裂纹的增多,矿物颗粒间的黏结力也在水的作用下降低从而使页岩的抗拉强度下降。  相似文献   

粤东后江湾冲流带滩面高频振动及动力作用分析     

冯砚青  陈子燊  李志龙  李志强 《海洋科学进展》2005,23(2):174-182

利用涌浪影响下短时段内的冲流带滩面高频高程数据和碎波带波流资料,在奇异谱分析(SSA)的基础上,对比研究了不同形态滩面的冲淤变化趋势、趋势分布形状、冲淤变化周期和冲淤变化强度,以及同一条剖面不同桩点间各因素间的变化关系;用交叉谱方法探索了每分钟滩面高频冲淤变化与碎波带长重力波间的作用关系。分析结果表明,滩角韵律地形引起的冲流分流作用促进了滩脊向滩谷的泥沙转运,冲流带滩面存在明显的长重力波频段的周期性冲淤振动,滩面冲淤振动强度由滩面下部向上部递减,碎波带长重力波对滩面高频冲淤变化起重要作用。  相似文献