Epicyclic oscillation modes of a Newtonian,non‐slender torus     

E. &#x;rmkov 《Astronomische Nachrichten》2005,326(9):835-837

All normal modes of oscillations of slender tori have been expressed analytically in the classic work by Blaes (1985). We adopt his approach in order to calculate the eigenfunctions and eigenfrequencies of a particular class of epicyclic modes for slightly non‐slender tori, and present results of our numerical simulation of torus epicyclic modes of oscillations, which will be compared with the analytical results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The onset of General Relativity: gravitationally redshifted emission lines     

A. Müller 《Astronomische Nachrichten》2006,327(10):1024-1027

We study and quantify gravitational redshift by means of relativistic ray tracing simulations of emission lines. The emitter model is based on thin, Keplerian rotating rings in the equatorial plane of a rotating black hole. Emission lines are characterised by a generalized fully relativistic Doppler factor or redshift associated with the line core. Two modes of gravitational redshift, shift and distortion, become stronger with the emitting region closer to the Kerr black hole. Shifts of the line cores reveal an effect at levels of 0.0015 to 60% at gravitational radii ranging from 10⁵ to 2. The corresponding Doppler factors range from 0.999985 to 0.4048. Line shape distortion by strong gravity, i.e. very skewed and asymmetric lines occur at radii smaller than roughly ten gravitational radii. Gravitational redshift decreases with distance to the black hole but remains finite due to the asymptotical flatness of black hole space–time. The onset of gravitational redshift can be tested observationally with sufficient spectral resolution. Assuming a resolving power of ∼100000, yielding a resolution of ≈0.1 Å for optical and near‐infrared broad emission lines, the gravitational redshift can be probed out to approximately 75000 gravitational radii. In general, gravitational redshift is an indicator of black hole mass and spin as well as for the inclination angle of the emitter, e.g. an accretion disk. We suggest to do multi‐wavelength observations because all redshifted features should point towards the same central mass. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

光照碾压混凝土大坝渗控分析     

荣冠  周创兵 《岩土力学》2006,27(Z2):429-434

基于光照水电站坝基水文地质条件及坝体渗透特性的研究,建立了大坝三维有限元模型,模型较详细地考虑了坝体大坝不防渗结构和排水系统及坝基地质和防排渗结构。分析研究了薄层单元、排水孔幕的模拟方法,采用合适的方法计算了同条件下的渗控情况。通过综合对比分析,对该坝的渗流规律及相应渗控措施进行了初步地探讨。  相似文献   

第四系深厚洪积物内成洞条件工程地质研究     

李院忠 《岩土力学》2006,27(Z2):601-606

经过对不同时期洪积物的成因、物质组成、结构、构造等的分析,以及对第一期洪积物内能否成洞的试验性模拟开挖、观察、分析,并在大量室内外物理力学性质试验的基础上,分析、量化出洪积物内成洞工程地质特性参数。在精心设计和施工下,深厚洪积物内开挖大跨度洞室顺利成功。  相似文献   

金沙峡电站闸坝区渗流场有限体积法数值模拟   总被引：2，自引：0，他引：2  

杨海英  陈刚  柴军瑞  张志昌 《岩土力学》2005,26(3):461-464

为实现泄冲闸、进水闸和土坝结合部位三维渗流场真实区域的数值模拟,采用有限体积法对含排水孔在内的闸坝区三维渗流场进行了网格划分。根据计算结果可知,闸基处防渗墙效果微弱,溢出点垂直坡降大于允许值,对工程不利,并提出了相应的改进措施。  相似文献   

单轴压缩下含孔脆性材料的力学行为研究   总被引：3，自引：1，他引：2  

段进超  唐春安  常旭  陈奇栓 《岩土力学》2006,27(8):1416-1420

运用材料破裂过程分析MFPA2D系统,在单轴压缩条件下对含单孔和双孔脆性材料破坏过程进行数值模拟。结果表明：原始的萌生裂纹不一定是最后形成宏观贯通破坏的主裂纹。岩石等脆性材料破坏的局部化特征,说明非均匀性是岩石类脆性材料发生局部破裂的根本原因。分析了孔的分布对材料强度以及破坏模式的影响,并给出破坏过程的应力-应变关系。指出了有的孔洞分布会增加应力的集中程度,而有的孔洞分布可以降低应力集中。数值模拟与试验结果具有较好的一致性。  相似文献   

阳泉矿区瓦斯抽放方式及优选原则   总被引：3，自引：1，他引：2  

张吉林  卫东  蔡锋光 《煤田地质与勘探》2001,29(4):17-19

针对阳泉矿区瓦斯赋存特点,通过对比分析各类瓦斯抽放方式指标,从而得出经济、技术可行的最优抽放方式;阳泉矿区单一煤层采用U+L型通风方式的工作面,大口径钻孔抽放方式是最佳选择和发展方向;15#煤层综放工作面采用U型通风方式和走向顶板岩巷抽放方式比较优越。   相似文献   

Measuring solar irradiance profiles in the Arctic sea ice using fiber optic spectrometry via inclined holes     

Zexia Qiu  Hangzhou Wang  Tao Li  Hong Song  Yuanqian Wu  Tingting Yan  Ying Chen 《海洋学报(英文版)》2021,40(3):134-141

An irradiance profile measurement approach and profiling system were developed to measure the solar irradiance profile of the Arctic sea ice using fiber optic spectrometry. The approach involved using a miniature spectrometer to sense light signals collected and transmitted from a fiber probe. The fiber probe was small, and could thus move freely in inclined bore holes drilled in sea ice with its optical entrance pointing upward. The input-output relationship of the system was analyzed and built. Influence factors that determined the system output were analyzed. A correctional system output approach was proposed to correct the influence of these factors, and to obtain the solar irradiance profile based on the measurements outputted by this system. The overall performance of the system was examined in two ice floes in the Arctic during the 9 th Chinese National Arctic Research Expedition. The measured solar irradiance profiles were in good agreement with those obtained using other commercially available oceanographic radiometers. The derived apparent optical properties of sea ice were comparable to those of similar sea ice measured by other optical instruments.  相似文献   

Characterization of horseshoe vortex in a developing scour hole at a cylindrical bridge pier   总被引：1，自引：0，他引：1  

Dawei Guan  Yee-Meng Chiew  Maoxing Wei  Shih-Chun Hsieh 《国际泥沙研究》2019,34(2):118-124

Since local scour at bridge piers in rivers and estuaries is a major cause of bridge failure, estimation of the maximum local scour depth is of great importance to hydraulic and coastal engineers. Although numerous studies that focus on scour-depth prediction have been done and published, understanding of the flow and turbulence characteristics of the horseshoe vortex that drives the scour mechanism in a developing scour hole still is immature. This study aims to quantify the detailed turbulent flow field in a developing clear-water scour hole at a circular pier using Particle Image Velocimetry (PIV). The distributions of velocity fields, turbulence intensities, and Reynolds shear stresses of the horseshoe vortex that form in front of the pier at different scour stages (t=0, 0.5, 1, 12, 24, and 48 h) are presented in this paper. During scour development, the horseshoe vortex system was found to evolve from one initially small vortex to three vortices. The strength and size of the main vortex are found to increase with increasing scour depth. The regions of both the maximum turbulence intensity and Reynolds shear stress are found to form at a location upstream of the main vortex, where the large turbulent eddies have the highest possibility of occurrence. Results from this study not only provide new insight into the complex flow-sediment interaction at bridge piers, but also provide valuable experimental databases for advanced numerical simulations.  相似文献   

Reconstructing rates and patterns of colluvial soil redistribution in agrarian (hummocky) landscapes     

W.M. van der Meij  T. Reimann  V.K. Vornehm  A.J.A.M. Temme  J. Wallinga  R. van Beek  M. Sommer 《地球表面变化过程与地形》2019,44(12):2408-2422

Humans have triggered or accelerated erosion processes since prehistoric times through agricultural practices. Optically stimulated luminescence (OSL) is widely used to quantify phases and rates of the corresponding landscape change, by measuring the last moment of daylight exposure of sediments. However, natural and anthropogenic mixing processes, such as bioturbation and tillage, complicate the use of OSL as grains of different depositional ages become mixed, and grains become exposed to light even long after the depositional event of interest. Instead, OSL determines the stabilization age, indicating when sediments were buried below the active mixing zone. These stabilization ages can cause systematic underestimation when calculating deposition rates. Our focus is on colluvial deposition in a kettle hole in the Uckermark region, northeastern Germany. We took 32 samples from five locations in the colluvium filling the kettle hole to study both spatial and temporal patterns in colluviation. We combined OSL dating with advanced age modelling to determine the stabilization age of colluvial sediments. These ages were combined with an archaeological reconstruction of historical ploughing depths to derive the levels of the soil surface at the moment of stabilization; the deposition depths, which were then used to calculate unbiased deposition rates. We identified two phases of colluvial deposition. The oldest deposits (~5 ka) were located at the fringe of the kettle hole and accumulated relatively slowly, whereas the youngest deposits (<0.3 ka) rapidly filled the central kettle hole with rates of two orders of magnitude higher. We suggest that the latter phase is related to artificial drainage, facilitating accessibility in the central depression for agricultural practices. Our results show the need for numerical dating techniques that take archaeological and soil-geomorphological information into account to identify spatiotemporal patterns of landscape change, and to correctly interpret landscape dynamics in anthropogenically influenced hilly landscapes. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.  相似文献