钻井中首波的共振与衰减   总被引：6，自引：2，他引：4  

董庆德  王克协 《地球物理学报》1991,34(2):228-239

本文从P波首波的严格割线积分出发,首次给出了揭示其共振与衰减特性的渐近展开式,通过数值计算,对这些公式进行了检验,证明它们与严格解符合的相当好.解析的和数值结果一致表明:首波具有共振特性,频谱是连续的;振幅随源距z按1/z规律衰减;各共振峰幅度随岩石泊松比v的增大按[v/（1-v）]²规律增大.时域计算表明,所谓“滤波效应”正是首波共振激发特性的反映,传播过程中不频散.  相似文献   

Secular resonances in the primitive solar nebula     

Anne Lemaitre  Pierre Dubru 《Celestial Mechanics and Dynamical Astronomy》1991,52(1):57-78

We present here a very simple model that could explain the relatively high eccentricities and inclinations observed in the minor planet belt. This model is based upon the sweeping of the secular resonances ₆ and ₁₆ through the belt due to the gravitational effect of the dissipation of a primitive solar nebula. The sweeping of the ₁₆ secular resonance (responsible for the high inclinations) is very sensitive to the density profile of the nebula. For the model to work we need a density profile proportional to ^–k with between 1.0 and 1.5.  相似文献   

Technical Note Characteristics of ground vibrations and structural response to surface and underground blasting     

Pijush Pal Roy 《Geotechnical and Geological Engineering》1998,16(2):151-166

The author considers the structural response of various types of surface structures along with their resonance characteristics as well as magnification and attenuation problems. Experimental data from 20 different mines in India, are compiled and analysed to develop simple general equations for use in field conditions. Interpretation of low frequency waves and their active role in enhancing damage probability of structures is also discussed. Particular situations are examined where low and high dominant band frequencies could obtain. It is suggested that a response analysis be undertaken before establishing damage threshold values of any type of structure. © Rapid Science Ltd. 1998  相似文献   

颈椎病的CT,CTM,MRI扫描诊断165例分析     

阮彦  徐建民 《CT理论与应用研究》1995,4(3):17-18

本文回顾性的报告分析了１６５例颈椎病，ＣＴ５０例、ＣＴＭ１５例、ＭＲＩ１００例。ＭＲＩ比ＣＴ和ＣＴＭ更精确而且没有损害。但ＣＴ和ＣＴＭ则可补充ＭＲＩ对颈椎和韧带的观察不足。三种方法的结合使用，将对临床诊断和治疗起重要作用。  相似文献   

柱状扰动体引起圆柱谐振腔共振频率偏移的数值模拟   总被引：8，自引：1，他引：7       下载免费PDF全文

Harris J M  徐德龙  王秀明  宋延杰  丛健生  陈德华 《地球物理学报》2005,48(2):445-451

基于微扰理论,研究了内部存在一个同轴圆柱扰动体时圆柱谐振腔共振频率的偏移问题.其中,圆柱谐振腔的边侧面是刚性的,上下底面应力自由.经过推导,得出了圆柱扰动体存在时谐振腔的声势与共振频率的表达式.在此基础上,分析了谐振腔与圆柱扰动体各种参数对谐振腔共振频率的影响.数值模拟结果表明,谐振腔的共振频率受扰动体在谐振腔中的位置影响较大.圆柱谐振腔的共振频率在圆柱扰动体居中时是最大值,并且其共振频率对扰动体的声速敏感;当扰动体在谐振腔两端时,谐振腔共振频率是最小值,并且其对扰动体的密度敏感.最后,通过数值模拟结果和实验测量结果之间的对比,发现两者的基本变化趋势是吻合的.  相似文献   

基于地球-电离层空腔共振的地震电磁监测方法研究   总被引：1，自引：0，他引：1  

曹丙霞  乔晓林 《国际地震动态》2009,(7):22-26

多年来的观测研究表明,地震活动可能引发地球．电离层空腔共振异常。本文介绍了地球-电离层空腔共振的产生机理,主要的特征参数以及常用的观测方法等。总结了目前国际上对共振异常现象与地震活动关系的主要分析方法和研究结果。对地震活动引发地球-电离层空腔共振异常的下一步研究工作进行了探讨。  相似文献   

Dynamic properties of the Quaternary sedimentary rocks and their influence on seismic site effects. Case study in Bucharest City,Romania     

Andrei Bala  Bogdan Grecu  Viorica Ciugudean  Victor Raileanu 《Soil Dynamics and Earthquake Engineering》2009

Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildings with 6–9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure upon ground motion parameters. New seismic measurements are performed in Bucharest area aiming at defining better elastic and dynamic properties of the shallow sedimentary rocks. Down-hole seismic measurements were performed in a number of 10 cased boreholes drilled in the Bucharest City area. Processing and interpretation of the data lead to the conclusion that shallow sedimentary rocks can be considered weak in the area, down to 150–200 m depth. Seismic wave velocity values and bulk density values presented in the paper associated with local geology are useful primary data in the seismic microzonation of Bucharest City. They are used as 1D models to derive transfer functions and response spectra for the stack of sedimentary rocks in several parts of Bucharest area, leading to a better knowledge of the local site amplification and associated frequency spectra. In a recent study the H/V spectral ratio using Nakamura’s method was applied on the seismic noise measurements in 22 sites in Bucharest City in order to derive the fundamental period associated with these sites. The values confirm the previous results, showing a dominant resonance in the period range of 1.25–1.75 s. The fundamental periods obtained with Nakamura’s method are in good agreement with those computed on the basis of geological and geotechnical data in boreholes, which show an increase of the fundamental period in the Bucharest area from south to north, in the same direction as the increase of the thickness of the Quaternary deposits above the Fratesti layer which is considered the bedrock in the area.  相似文献   

Pore size distributions and hydraulic conductivities of rocks derived from Magnetic Resonance Sounding relaxation data using multi-exponential decay time inversion   总被引：3，自引：0，他引：3  

O. Mohnke  U. Yaramanci   《Journal of Applied Geophysics》2008,66(3-4):73

In hydrogeology there is a variety of empirical formulae available for determination of hydraulic conductivity of porous media, all based on the analysis of grain size distributions of aquifer materials. Sensitivity of NMR measurements to pore sizes makes it a good indicator of hydraulic conductivity. Analogous to laboratory NMR, Magnetic Resonance Sounding (MRS) relaxation data are of a multi-exponential (ME) nature due to the distribution of different pore sizes in an investigated rock layer. ME relaxation behaviour will also arise due to the superposition of NMR signals which originate from different layers. It has been shown, that both kinds of ME behaviour coexist in MRS and can principally be separated by ME inversion of the field data. Only a few publications exist that have proposed approaches to qualitatively and quantitatively estimate petrophysical parameters such as the hydraulic conductivity from MRS measurements, i.e. MRS porosity and decay times. The so far used relations for the estimation of hydraulic conductivity in hydrogeology and NMR experiments are compared and discussed with respect to their applicability in MRS. Taking into account results from a variety of laboratory NMR and MRS experiments mean rock specific calibration factors are introduced for a data-base-calibrated estimation of hydraulic conductivity when no on-site calibration of MRS is available. Field data have been analysed using conventional and ME inversion using such mean calibration values. The results for conventional and ME inversion agree with estimates obtained from well core analysis for shallow depths but are significantly improved using a ME inversion approach for greater depths.  相似文献   

Revelations from a single strong-motion record retrieved during the 27 June 1998 Adana (Turkey) earthquake     

M. elebi 《Soil Dynamics and Earthquake Engineering》2000,20(5-8):283-288

During the 27 June 1998 Adana (Turkey) earthquake, only one strong-motion record was retrieved in the region where the most damage occurred. This single record from the station in Ceyhan, approximately 15 km from the epicenter of that earthquake, exhibits characteristics that are related to the dominant frequencies of the ground and structures.

The purpose of this paper is to explain the causes of the damage as inferred from both field observations and the characteristics of a single strong-motion record retrieved from the immediate epicentral area. In the town of Ceyhan there was considerable but selective damage to a significant number of mid-rise (7–12 stories high) buildings. The strong-motion record exhibits dominant frequencies that are typically similar for the mid-rise building structures. This is further supported by spectral ratios derived using Nakamura's method [QR of RTRI, 30 (1989) 25] that facilitates computation of a spectral ratio from a single tri-axial record as the ratio of amplitude spectrum of horizontal component to that of the vertical component [R=H(f)/V(f)]. The correlation between the damage and the characteristics exhibited from the single strong-motion record is remarkable.

Although deficient construction practices played a significant role in the extent of damage to the mid-rise buildings, it is clear that site resonance also contributed to the detrimental fate of most of the mid-rise buildings. Therefore, even a single record can be useful to explain the effect of site resonance on building response and performance. Such information can be very useful for developing zonation criteria in similar alluvial valleys.  相似文献   

Resonances of low orders in the planetary system of HD37124     

Roman V. Baluev 《Celestial Mechanics and Dynamical Astronomy》2008,102(4):297-325

The full set of published radial velocity data (52 measurements from Keck + 58 ones from ELODIE + 17 ones from CORALIE) for the star HD37124 is analysed. Two families of dynamically stable high-eccentricity orbital solutions for the planetary system are found. In the first one, the outer planets c and d are trapped in the 2/1 mean-motion resonance. The second family of solutions corresponds to the 5/2 mean-motion resonance between these planets. In both families, the planets are locked in (or close to) an apsidal corotation resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation (with the difference between the longitudes of periastra Δω ~ 60°), whereas in the case of the 5/2 MMR it is a symmetric antialigned one (Δω = 180°). It remains also possible that the two outer planets are not trapped in an orbital resonance. Then their orbital eccentricities should be relatively small (less than, say, 0.15) and the ratio of their orbital periods is unlikely to exceed 2.3 − 2.5.  相似文献