三角高程测量在高速公路控制测量中的应用研究     

刘浩  刘建国 《地理空间信息》2008,6(1):111-113

根据山区地形特点,针对高速公路高程控制测量中应用的几种三角高程测量方法,对其原理、测量方法、公式、误差来源和适应性,进行了比较和分析,在此基础上提出了在山区高速公路控制测量中保证三角高程测量精度的措施的建议。  相似文献   

Preservation of old U–Th–Pb ages in shielded monazite: example from the Beni Bousera Hercynian kinzigites (Morocco)     

Montel  Kornprobst  & Vielzeuf 《Journal of Metamorphic Geology》2000,18(3):335-342.

Four samples from the metamorphic aureole around the Beni Bousera ultramafic massif were studied in detail for U–Th–Pb electron microprobe dating on monazite. The samples include three meta-sedimentary granulites (kinzigites), collected at variable distance from the peridotites, and one kyanite-bearing leucosome in the kinzigite. Two types of monazite were identified in thin section, using SEM. The main population consists of interstitial grains, 20–70  μ m in size, while the second population consists of small grains (<20  μ m), included in garnet. A total of 64 U–Th–Pb electron microprobe measurements on 53 monazite crystals were undertaken. Most crystals have a Pb content lower than the Pb detection limit, indicating that they crystallized, or were reset, during a young event, probably Cainozoic in age. Few crystals, all entirely included in garnet, have Hercynian age, the best estimate of which is 284±27 Ma. This is a direct demonstration of the shielding effect of garnet for the U–Th–Pb system in monazite. The grains in inclusion in garnet are not reset by the post-Hercynian events, despite the high temperature reached at this time (>850 °C). Thus, the monazite closure temperature depends on its textural position in the host rock. The data also show that a Hercynian event occurred in the Beni Bousera granulitic metapelites, which equates with a high- P , high- T  event. The emplacement of the peridotite in the Cainozoic may be linked a low- P , high- T  event, followed by a low- P , low- T  retrogression. These two events reset the U–Th–Pb system in almost all monazite grains, except for the few crystals shielded by garnet.  相似文献   

Influence of thermal stratification on the surfacing and clustering of floaters in free surface turbulence     

《Advances in water resources》2014

The dispersion of floaters, small organic particles lighter than water, on the free surface of an open turbulent channel flow subject to thermal stratification is studied by Direct Numerical Simulation (DNS) of turbulence and Lagrangian Particle Tracking (LPT). Constant heat flux is maintained at the free surface of the channel, the bottom wall is adiabatic and the turbulent flow is driven by a pressure gradient. This archetypal flow setup mimics an environmentally plausible situation which can be found in terrestrial water bodies. The free surface turbulence characteristic of such flows has a strong influence on the distribution of the floaters: the objective of this work is to study the effect of different regimes of stable stratification on the surface distribution of floaters. The distribution of the floaters can possibly influence the transfer of chemical species across the water/atmosphere interface. Our results show that the modification of turbulence due to the thermal stratification strongly influences the settling velocity of floaters in the bulk of the flow. At the surface, stratification effects are also observed on the clustering of the floaters: the filamentary patterns of floaters observed in unstratified turbulence are progressively lost as thermal stratification increases, and the distribution of the floaters remains roughly two-dimensional.  相似文献   

EPSW电子测绘系统在三峡工程明渠截流中的应用   总被引：1，自引：1，他引：0  

柳长征 《地理空间信息》2004,2(2):36-38

在三峡工程明渠截流进程中,截流戗堤左右头平面位置是一个动态轨迹。采用Trimble激光全站仪配合清华山维EPSW98电子测绘系统实时监测戗堤口门水面宽,方便、快捷、可靠且测量精度高,并解决了采用人工施测可能造成的安全问题。还介绍了采用EPSW电子测绘系统在水下地形测量数据自动成图中的应用,大大提高了出图效率,减少了出错环节。  相似文献   

近地层能量闭合度对陆面过程模式影响   总被引：1，自引：0，他引：1       下载免费PDF全文

杨启东  左洪超  杨扬  陈继伟  李强  赵静 《地球物理学报》2012,55(9):2876-2888

大量近地层观测试验表明,利用涡动相关法观测的湍流通量小于近地层可利用能量,即近地层能量是不闭合的,这种不闭合度一般为20%甚至更高.而陆面过程模式是基于地气间能量平衡建立,并且模式中的湍流边界层参数化方案通常根据实际观测的湍流通量来确定,因此能量不闭合必将对陆面过程模式造成一定的影响.本文利用2007年春季SACOL站的近地层观测资料,依据能量守恒将能量不闭合中的残余能量通过波文比分配到观测的湍流通量中,即修正涡动相关法观测的湍流通量使得近地层能量达到平衡;之后分别利用观测和修正的湍流通量,建立了能量不闭合和闭合情形下的湍流参数化方案,借助陆面过程模式SHAW,通过数值模拟和对比分析方法考察近地层能量闭合度对陆面过程模式的影响.研究结果表明近地层能量闭合对陆面过程模式有显著的影响:在陆面过程数值模拟中,当应用近地层能量不闭合的湍流通量形成的湍流参数化方案时,陆面过程模式会明显高估地表长波辐射及土壤温度;但当应用修正湍流通量使得近地层能量达到闭合形成的湍流参数化方案后,在不改变任何地表土壤物理生化属性的情况下,陆面过程模式能较好地模拟地表长波辐射和土壤温度.  相似文献   

重庆市多年大气混合层厚度变化特征及其对空气质量的影响分析   总被引：8，自引：0，他引：8       下载免费PDF全文

叶堤  王飞  陈德蓉 《气象与环境学报》2008,24(4):41-44

根据2000—2005年逐日4个时次的常规气象资料,采用国家标准GB/T 3840—91中规定的方法计算并分析了重庆主城区大气混合层厚度的频率分布、时间变化等基本特征;在此基础上,进一步以2005年为例分析了混合层厚度与空气污染指数的相关关系。结果表明:重庆市大气混合层厚度以0—800 m范围出现频率最高,多年平均值为428 m;混合层厚度的季节变化和日变化特征明显。与1980—1990年相比,2000—2005年期间年平均混合层厚度总体上有所增加。混合层厚度与空气污染指数的相关性分析显示,月平均混合层厚度和月平均API呈显著负相关(r=-0.72);分析表明,大气混合层厚度是影响城市空气质量的重要因素。  相似文献   

考虑初始损伤和残余强度的岩石变形过程模拟          下载免费PDF全文

温韬  唐辉明  马俊伟  张俊荣  范志强 《地球科学》2019,44(2):652-663

针对现有损伤模型的不足,提出同时反映岩石初始损伤和残余强度的岩石变形过程模拟方法.将岩石材料分为未损伤部分、损伤部分和微缺陷,未损伤部分和损伤部分共同承担岩石所受的应力.通过岩石材料几何条件及微观受力分析建立未损伤部分的应变分析.再考虑岩石的形变比能只与损伤部分材料相关,从而建立损伤部分的应变分析.然后探讨岩石损伤和耗散能的关系,提出了可以反映岩石初始损伤的损伤演化方程,基于各部分应变分析建立模拟岩石变形过程的损伤本构模型,同时给出模型各参数的确定方法.结果表明:损伤演化方程不仅表现了岩石的初始损伤特征,也可以完整地体现岩石变形破坏过程的5个阶段;与前人模型相比,提出的岩石变形模拟方法与试验曲线更加吻合,体现了岩石的变形全过程,特别是更加直观地反映了岩石的初始损伤和残余强度特征.综合体现了本文模型在模拟岩石变形全过程时的优势.  相似文献   

Mean flow and turbulence around experimental spur dike     

Jennifer G. Duan  Li He  Xudong Fu  Quangqian Wang 《Advances in water resources》2009

  相似文献   

委内瑞拉奥里诺科重油带J区块新老二维地震资料精细匹配处理及构造特征分析   总被引：1，自引：1，他引：0       下载免费PDF全文

韩国庆  穆龙新  姜建平 《地球物理学进展》2009,24(1):238-245

针对委内瑞拉奥里诺科重油带J区块新老二维地震资料存在的问题,应用精细匹配处理方法,即以精细频率匹配和精细振幅匹配和相位校正为主要手段,结合时间偏移处理以及去噪、混波处理等手段,普遍突出了有效反射信息,提高了不同年度地震剖面之间的闭合精度,大大提高了构造解释的准确性,虽然地震资料很少,但仍解释出了J区块的三层构造图,构造解释结果表明,J区块地层总体是一个北倾单斜,其上发育一些北东和近东西向的断层,油藏类型以岩性油藏为主,断层对油藏主要起复杂化作用,J区块这一构造特征与其所处的构造背景、基底形态和构造应力作用有关.  相似文献   

Calculation of primary and secondary flow and boundary shear stresses in a meandering channel     

Thorsten Stoesser  Nils Ruether  Nils Reidar Boe Olsen 《Advances in water resources》2010

Turbulent flow in a meandering channel is computed with two Computational Fluid Dynamics (CFD) codes solving the Navier–Stokes equations by employing different turbulence closure approaches. The first CFD code solves the steady Reynolds-Averaged Navier–Stokes equations (RANS) using an isotropic turbulence closure. The second code is based on the concept of Large Eddy Simulation (LES). LES resolves the large-scale turbulence structures in the flow and is known to outperform RANS models in flows in which large-scale structures dominate the statistics. The results obtained from the two codes are compared with experimental data from a physical model study. Both, LES and RANS simulation, predict the primary helical flow pattern in the meander as well as the occurrence of an outer-bank secondary cell. Computed primary as well as secondary flow velocities are in reasonably good agreement with experimental data. Evidence is given that the outer-bank secondary cell in a meander bend is the residual of the main secondary cell of the previous bend. However, the RANS code, regardless of the turbulence model employed, overpredicts the size and strength of the outer-bank secondary cell. Furthermore, only LES is able to uphold the outer-bank second secondary cell beyond the bend apex until the exit of the bend as turbulence anisotropy contributes to its persistence. The presence of multiple secondary cells has important consequences for the distribution of shear stresses along the wetted perimeter of the channel, and thereby the sediment transport in meandering channels. Consequently, even though LES is expected to compute the bed-shear stresses along the wetted perimeter of the channel with a higher degree of accuracy than the RANS model, comparisons between LES and RANS computed wall shear stresses agree well. These findings are useful for practitioners who need to rely on RANS model predictions of the flow in meandering channels at field scale.  相似文献