共查询到20条相似文献，搜索用时 15 毫秒
1.
The behavior of radial oscillations of coronal magnetic tubes is considered in a weakly nonlinear approximation. The nonlinear Schrödinger equation, the coefficients of which are found from the tube and radial mode parameters, has been obtained for the oscillation amplitude. The coefficients have been calculated for the fundamental radial mode, which is characterized by the absence of the cutoff in the region of low frequencies. It has been shown that the modulation instability condition is satisfied in a wide range of mode parameter values, which indicates that large-amplitude radial oscillations can exist in coronal loops. 相似文献
2.
一种测试动三轴试样泊松比的方法 总被引：1，自引：0，他引：1
利用非接触式位移传感器研制了一套测量动三轴试样径向变形的装置。针对试样两端透水石对试样径向变形的约束,推导了对实测径向变形的修正关系。利用径向与轴向变形测量装置,就可以依据实测动三轴试样的轴向与径向变形确定其泊松比。通过橡胶、饱和细砂、饱和软粘土试样固结不排水动三轴试验与结果分析,说明利用这里提出的方法可以比较客观地确定动三轴试样的泊松比。这里的研究结果还表明,固结后的饱和三轴土样在不排水条件下受振动应力作用时,当其轴向动应变从10-5增大至10-3时,泊松比的变化基本为一常数,且与固结压力的大小无关,将其取为接近0.5是合理的。 相似文献
3.
The evaluation of shear strains under multi-directional shaking is an important issue in interpreting dynamic soil behavior for both laboratory physical modeling and in situ monitoring. Shear strain components evaluated from Cartesian coordinates in undrained conditions have limitations to fully capture the coupled shear strain-pore pressure responses with an individual expression. In the present study, radial and rotational shear strain components derived from particle motions described with cylindrical polar coordinates are proposed. The proposed radial and rotational shear strains are verified with data from a bi-directional laminar shear box and a free field downhole array. Comparison results show that the proposed expressions of shear strain effectively capture the coupled strain-pore pressure responses in terms of the frequency content, amplitude variation, phase difference, and oscillation behavior. Comparison results reveal that the radial shear strain is the dominant shearing mode and the amplitude of the rotational shear strain is only 6.5–14.5% of the radial component. This provides quantitative data for the correction factor for multi-directional shaking and suggests that a simple shear system capable of inducing the radial shear strain on the vertical plane is a better approach than other shearing modes for physically modeling the behavior of soil subjected to undrained seismic loadings. 相似文献
4.
本文针对地层横波慢度径向分层模型,分析了地层横波慢度的径向非均匀性对弯曲波频散的影响.基于径向非均匀与均匀模型之间弯曲波频散的差异,结合微扰法和Backus-Gilbert(BG)理论建立了反演横波慢度径向分布的方程,求取了地层横波慢度的径向分布.在无噪声和参数误差时,反演结果较好地反映了实际地层横波慢度的径向分布,当井孔流体或井外地层纵波慢度的选取误差在10%内变化时,反演结果基本保持不变;存在信噪比(SNR)为20 dB(信号的功率为噪声的100倍)或10 dB(信号的功率为噪声的10倍)噪声时,反演结果没有发生明显的改变,其相对误差基本控制在10%以内,可见噪声对反演结果的影响不大.以上反演结果说明,本文采用的结合微扰法和BG理论的反演方法来估测地层横波慢度的径向分布时,具有很好的鲁棒性,可以被用于现场了解井壁周围的地层性质. 相似文献
5.
Mehdi Eshagh 《Journal of Geodynamics》2010,49(2):92-104
The gravity anomalies at sea level can be used to validate the satellite gravity gradiometry data. Validation of such a data is important prior to downward continuation because of amplification of the data errors through this process. In this paper the second-order radial derivative of the extended Stokes’ formula is employed and the emphasis is on least-squares modification of this formula to generate the second-order radial gradient at satellite level. Two methods in this respect are proposed: (a) modifying the second-order radial derivative of extended Stokes’ formula directly, and (b) modifying extended Stokes’ formula prior to taking the second-order radial derivative. Numerical studies show that the former method works well but the latter is very sensitive to the proper choice of the cap size of integration and degree of modification. 相似文献
6.
针对声波测井中采用的柱状薄圆管压电换能器,提出一种研究换能器响应的解析方法.该方法考虑了轴向与径向振动之间的耦合作用,导出置于耦合液体中压电换能器径向位移满足的微分方程和频域传递函数,比较分析了不同激励源作用下换能器的位移响应特性.利用波数域实轴积分法,计算了换能器在弹性地层井孔中激发的声场,研究了不同地层中的波形差异.与前人在假定声源强度的模型下只能求出波场的相对幅度不同,本文得出在一定激励电压作用下换能器在井孔中激发声场的幅度值.这为说明声波测井响应信号的强弱及仪器的声系设计提供了依据,对估计动电效应测井信号的强弱有参考意义. 相似文献
7.
云南地区地处青藏高原东南缘,一直是地球科学研究的热点地区.目前,一些热点问题,如云南地区是否存在中下地壳低速流及其空间分布,仍有一定的争议.通过建立云南地区精细的地壳上地幔速度与各向异性结构,可为深入认识上述问题提供重要信息.本文利用天然地震波形记录,采用双台法提取了12~60 s周期的Rayleigh和Love波相速度频散,并进一步反演获得了云南地区10~100 km的三维地壳上地幔SV和SH波速度及径向各向异性结构.结果表明：S波速度与径向各向异性结构在横向和垂向均存在显著变化.在20~30 km深度,存在两个低速条带,且条带内呈现出正径向各向异性（VSH>VSV）特征,暗示了中下地壳低速物质的水平向运动.在80~100 km深度,云南西南和东南部显示为低速异常和正径向各向异性特征,暗示了软流圈物质的水平流动.在云南北部的丽江、攀枝花和昭通地区,岩石圈地幔中则存在明显的负径向各向异性（VSH<VSV）,可能反映了地幔物质的上涌痕迹.历史强震多发生在地壳低速区域或高低速过渡带,且地震附近的径向各向异性为负或者较弱.一些地震震源下方存在低速层,地壳低速层可能会促进强震发生. 相似文献
8.
Vladimir Priklonsky Anvar Shukurov Dmitry Sokoloff Andrew Soward 《地球物理与天体物理流体动力学》2013,107(1-2):97-114
Abstract We reconsider thin-disc global asymptotics for kinematic, axisymmetric mean-field dynamos with vacuum boundary conditions. Non-local terms arising from a small but finite radial field component at the disc surface are consistently taken into account for quadrupole modes. As in earlier approaches, the solution splits into a local part describing the field distribution along the vertical direction and a radial part describing the radial (global) variation of the eigenfunction. However, the radial part of the eigenfunction is now governed by an integro-differential equation whose kernel has a weak (logarithmic) singularity. The integral term arises from non-local interactions of magnetic fields at different radii through vacuum outside the disc. The non-local interaction can have a stronger effect on the solution than the local radial diffusion in a thin disc, however the effect of the integral term is still qualitatively similar to magnetic diffusion. 相似文献
9.
A standard pair of equations is used to describe the behaviour of a single monoenergetic particle (proton or electron) population on a geomagnetic flux tube drifting in the magnetosphere. When particle losses from the drifting flux tube into the ionosphere are neglected, this behaviour is adiabatic in a thermodynamic sense. For a population of particles with an isotropic pitch-angle distribution, the generalization of that system of equations is obtained by adding radial and azimuthal spatial diffusion terms. The magnetic field is taken to be dipolar in the inner magnetosphere. The potential electric field is assumed to consist of magnetospheric convection and corotation components. Experimental data are used to estimate the radial equatorial profiles of the plasma sheet pressure. Assuming that the local time and L-shell variations are separable and supposing steady-state conditions, the expressions for the diffusion tensor components are evaluated. The influence of spatial diffusion on the radial and azimuthal profiles of the plasma pressure in the inner plasma sheet is also discussed. 相似文献
10.
套管外地层受异常地应力、油气开采的影响,在径向上表现出非均质性;采用声波测井可以对该非均质性进行探测,利用偶极子横波测井数据可以对横波速度的径向分布进行反演.本文建立了套管井外地层横波速度径向分层参考模型,采用修正的微扰法计算了该模型的偶极弯曲波频散曲线,建立了横波速度径向分布反演目标函数,采用高斯牛顿法和快速模拟退火法对目标函数进行了求解,得到了套管井外地层横波速度的径向分布.分析了偶极弯曲波频段、套管横波速度对反演结果的影响,对比了高斯牛顿法和快速模拟退火法对反演过程的影响.分析对比结果表明,采用偶极弯曲波激发强度较高的频段与采用全频段的反演结果相近;套管的横波速度准确度越高,反演结果越准确;高斯牛顿法和快速模拟退火法计算精度相同,都可以得到高精度的横波速度径向分布;快速模拟退火法的计算效率略低于高斯牛顿法,但其收敛性对初始值依赖更小,实际处理中应选择快速模拟退火法. 相似文献
11.
Surface current mapping from HF/VHF coastal radars traditionally requires at least two distant sites. Vector velocities are
estimated by combining the radial velocity components measured by the radars. In many circumstances (e.g., failures, interferences,
logistics constraints), such a combination is not possible by lack of data from one station. Two methods are evaluated to
get information on surface circulation from a single site radar: the Vectorial Reconstruction Method (VRM) for current vector
mapping and the Vortex Identification Method (VIM) for detecting eddy-like structures. The VRM assumes a non-divergent horizontal
surface current, and the VIM analyzes radial velocities and their radial and orthoradial gradients. These two methods are
tested on modeled and measured data sets in the Northwestern Mediterranean Sea where both high-resolution ocean circulation
model and radar campaigns are available. The VRM performance is strongly limited by the divergence-free hypothesis which was
not satisfied in our real data. The VIM succeeded in detection of vortex in the Gulf of Lions and from an operating single
site radar located on the Provence coasts in summer. 相似文献
12.
The paper gives relationships for predicting reservoir circulation generated by radial and tangential jets. These relationships show the importance of the reservoir's aspect-ratio, and the Reynolds number of the jet.Details are also given of concentration-experiments using the conductivity and fluorimetric methods, and incorporating various inlet and outlet arrangements. Peripheral and radial dispersion-coefficients were obtained, and found to be of the same order of magnitude. These coefficients were dependent on the size of the model and on the local Reynolds numbers. The values of dispersion coefficients for reservoirs are similar to those for one-dimensional open channel flow. 相似文献
13.
Axial and Radial Permeability Evolutions of Compressed Sandstones: End Effects and Shear-band Induced Permeability Anisotropy 总被引：2，自引：0，他引：2
Jeremie Dautriat Nicolas Gland Jean Guelard Alexandre Dimanov Jean L. Raphanel 《Pure and Applied Geophysics》2009,166(5-7):1037-1061
The influence of hydrostatic and uniaxial stress states on the porosity and permeability of sandstones has been investigated. The experimental procedure uses a special triaxial cell which allows permeability measurements in the axial and radial directions. The core sleeve is equipped with two pressure samplers placed distant from the ends. They provide mid-length axial permeability measure as opposed to the overall permeability measure, which is based on the flow imposed through the pistons of the triaxial cell. The core sleeve is also equipped to perform flows in two directions transverse to the axis of the sample. Two independent measures of axial and complementary radial permeability are thus obtained. Both Fontainebleau sandstone specimens with a porosity of about 5.8% to 8% and low permeability ranging from 2.5 mD to 30 mD and Bentheimer sandstone with a porosity of 24% and a high permeability of 3D have been tested. The initial axial permeability values obtained by each method are in good agreement for the Fontainebleau sandstone. The Bentheimer sandstone samples present an axial mid-length permeability 1.6 times higher than the overall permeability. A similar discrepancy is also observed in the radial direction, also it relates essentially to the shape of flow lines induced by the radial flow. All the tested samples have shown a higher stress dependency of overall and radial permeability than mid-length permeability. The effect of compaction damage at the pistons/sample and radial ports/sample interfaces is discussed. The relevance of directional permeability measurements during continuous uniaxial compression loadings has been shown on the Bentheimer sandstone until the failure of the sample. We can efficiently measure the influence of brittle failure associated to dilatant regime on the permeability: It tends to increase in the failure propagation direction and to decrease strongly in the transverse direction. 相似文献
14.
Igor Bashmachnikov Tatyana Belonenko Pavel Kuibin Denis Volkov Victor Foux 《Ocean Dynamics》2018,68(12):1711-1725
Mean radial distributions of various dynamic characteristics of the permanently existing anticyclonic Lofoten vortex (LV) in the Norwegian Sea are obtained from an eddy-permitting regional hydrodynamic MIT general circulation model. It is shown that the model adequately reproduces the observed 3D thermohaline and dynamic structure of the vortex. The obtained radial distribution of the mean vertical velocity is found to form a complex structure: with the upward fluxes along the axis in and above the anticyclonically rotating LV core, compensated by the downward fluxes in the vortex skirt. These vertical motions maintain the vortex potential energy anomaly against dissipation. This secondary circulation is generated by the centrifugal force and, to a lesser extent, by the horizontal dispersion of the vortex energy, both intensified towards the sea surface. Below the vortex core, the maximum downward vertical velocity converges towards the vortex axis with depth. At these depth levels, the secondary circulation is forced by Ekman divergence in the bottom mixed layer. The theory of columnar vortices with helical structure, applied to the LV, relate the radial profiles of the vertical velocity with those of the horizontal circulation. The theoretically predicted the radial patterns of the mean vertical velocity in the LV were close to those, obtained from the primitive equation ocean model, when approximating the radial patterns of the azimuthal velocity with the Rayleigh profile. 相似文献
15.
16.
利用2006-2010年的CloudSat热带气旋过境数据集资料,定量分析了大西洋地区飓风的云、降水和热力结构在不同演变阶段内的分布特征,结果表明:雷达反射率的发生概率以5 km高度为"拐点"呈现不同的分布特点,且成熟阶段的回波强度明显大于发展和消亡阶段.各径向环内深对流云发生概率始终最大,积云和雨层云始终最小.冰水含量的最大值位于内核区且沿径向不断减小,有效粒子半径和分布宽度参数随高度减小而粒子数浓度却增大.温度距平在距离中心200 km以内随飓风演变不断增大,而200 km以外始终较小.各阶段8 km以下存在湿心区,而其上方正好对应暖心区.内核区发展阶段存在近饱和区而成熟和消亡阶段存在向外倾斜的未饱和区.各阶段不同径向环内4 km以上主要为稳定层结而4 km以下的层结特性各异,且假相当位温沿径向逐渐减小. 相似文献
17.
本文首先指出经典粘性理论应适用于扇形边界低速风,接着论证了常用太阳风粘性数学表式的不正确性,导出了螺旋磁场中径向球对称强磁化等离子体流动的各种经典粘性表式,并证明了这些公式的合理性;最后讨论了常用太阳风经典粘性表式出错原因,估计了具有正确粘性公式的扇形边界低速太阳风粘性模式应有的结果。 相似文献
18.
S. Abhilash A. K. Sahai K. Mohankumar John P. George Someshwar Das 《Pure and Applied Geophysics》2012,169(11):2047-2070
In this paper the impact of Doppler weather radar (DWR) reflectivity and radial velocity observations for the short range forecasting of a tropical storm and associated rainfall event have been examined. Doppler radar observations of a tropical storm case that occurred during 29–30 October 2006 from SHARDWR (13.6° N, 80.2° E) are assimilated in the WRF 3DVAR system. The observation operator for radar reflectivity and radial velocity is included within latest version of WRF 3DVAR system. Keeping all model physics the same, three experiments were conducted at a horizontal resolution of 30?km. In the control experiment (CTRL), NCEP Final Analysis (FNL) interpolated to the model grid was used as the initial condition for 48-h free forecast. In the second experiment (NODWR), 6-h assimilation cycles have been carried out using all conventional (radiosonde and surface data) and non-conventional (satellite) observations from the Global Telecommunication System (GTS). The third experiment (DWR) is the same as the second, except Doppler radar radial velocity and reflectivity observations are also used in the assimilation cycle. Continuous 6-h assimilation cycle employed in the WRF-3DVAR system shows positive impact on the rainfall forecast. Assimilation of DWR data creates several small scale features near the storm centre. Additional sensitivity experiments were conducted to study the individual impact of reflectivity and radial velocity in the assimilation cycle. Radar data assimilation with reflectivity alone produced large analysis response on both thermodynamical and dynamical fields. However, radial velocity assimilation impacted only on dynamical fields. Analysis increments with radar reflectivity and radial velocity produce adjustments in both dynamical and thermodynamical fields. Verification of QPF skill shows that radar data assimilation has a considerable impact on the short range precipitation forecast. Improvement of the QPF skill with radar data assimilation is more clearly seen in the heavy rainfall (for thresholds >7?mm) event than light rainfall (for thresholds of 1 and 3?mm). The spatial pattern of rainfall is well simulated by the DWR experiment and is comparable to TRMM observations. 相似文献
19.
Mapping crustal S—wave velocity structure with SV—component receiver function method 总被引：1，自引：0，他引：1
In this article,we analyze the characters of SV-component receiver function of teleseismic body waves and its advantages in mapping the S-wave velocity structure of crust in detail.Similar to radial receiver function,SV-component receiver function can be obtained by directly deconvolving the P-component from the SV-component of teleseismic recordings.Our analyses indicate that the change of amplitude of SV-component receiver function against the change of epicentral distance is less than that of radial receiver function.Moreover,the waveform of SV-component receiver function is simpler than the radial receiver function and gives prominence to the PS converted phases that are the most sensitive to the shear wave velocity structure in the inversion.The synthetic tests show that the convergence of SV-component receiver function inversion is faster than tnat of the radial receiver function inversion.As an example,we investigate the S-wave velocity structure beneath HIA sta-tion by using the SV-component receiver function inversion method. 相似文献
20.
为研究过套管电阻率测井仪器的径向探测特性,本文给出了反映地层径向介质变化的几何因子.利用过套管电阻率测井的传输线方程实现了电阻率测井几何因子的数值计算,针对Schlumberger公司的CHFR测井仪和俄罗斯的ЭКОС-31-7测井仪分别计算了几何因子响应曲线,通过曲线分析发现：两种测井仪对低侵剖面（有低阻流体侵入）均有较大的探测半径,但随侵入流体电阻的增大（高侵剖面）仪器的径向探测半径在减小,本文的研究为地层电阻率测井解释和仪器径向探测特性分析提供了理论依据. 相似文献