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991.
The parameters of Earth free core nutation (FCN) are two relatively significant geophysical parameters. Sasao et al. (1980) and Wahr and Bergen (1986) provided the theoretical estimation values of FCN parameters. Gwinn, Herring and Shapiro (1987) first obtained the observational values of FCN parameters by very long base Interference (VLBI) at Cambridge University. In the same year, Neuberg and Zürn in former West Germany and Hinderer in France began to retrieve FCN parameters by the observation of gravity tides and introduced the stacking method. The other scholars who researched into the same geophysical problems by applying the data of gravity tides basically followed the stacking method. The results they reached were similar to the observational result of FCN parameters given by Neuberg et al. in 1987. But the observational results of FCN parameters gained from gravity tides were not identical with those from VLBI, mainly because of the large difference of quality of FCN. So there was not an affirmative observational result of FCN parameters since then. In this paper, The authors firstly introduce the tri-frequency spectrum method with clearly geometrical and geophysical meaning for the resolution of FCN parameters, and the observational results of FCN parameters obtained from tide data at three superconducting gravity stations were accordant with those from VLBI, which will be relatively important to arriving at a certain observational result of FCN parameters. 相似文献
992.
Juan C. Carvajal Víctor M. Taboada-Urtuzustegui Miguel P. Romo 《Soil Dynamics and Earthquake Engineering》2002,22(4)
The installation of vertical downhole arrays in the field that record the soil behavior during earthquakes, has opened the opportunity of exploring another alternate method for assessing the soil dynamic properties by solving the inverse problem. This article proposes a methodology for solving this problem using spectral analysis of downhole arrays records. The one-dimensional shear wave propagation model was used, considering a homogeneous-viscoelastic medium. This methodology was applied at the site known as Central de Abasto Oficinas (CAO), which is located in the lake zone of the Mexico City. The results indicate that even relatively low frequencies have a noticeable effect on dynamic soil properties. Shear modulus increases and damping ratio lessens when the frequency rises. 相似文献
993.
A simple procedure for identifying hysteretic properties of seismically isolated bridges from full‐scale quick‐release tests is presented in this paper. An analytical solution for the quick‐release response of a SDOF system with a bilinear spring is derived. Based on the solution, some characteristics of such systems are obtained. A time domain optimization method is employed to identify the hysteretic properties of the lead–rubber bearings installed in seismically isolated bridges. The total damping effects of the isolation system are expressed as a combination of the rate‐independent (hysteretic) damping and the linear viscous damping. The Menegotto–Pinto (MP) model and bilinear model are used to represent the force–displacement relation of the lead–rubber bearings. In both the longitudinal and transverse directions the bridges have been idealized as single degree of freedom (SDOF) systems. Time histories recorded from the field quick‐release tests on two bridges are used for the examples presented herein. The hysteretic loops of the isolators obtained from laboratory tests are compared with those obtained using the optimization method, and they agree well. In conclusion, the procedure shown in this paper can be used to identify the essential in situ hysteretic characteristics of isolation bearings from quick‐release field testing. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
994.
碳酸盐岩既可作为烃源岩,也可作为储集岩存在。因此,除直接发现液态石油和气苗外,在野外和室内碳酸盐岩含油的识别都较困难。确定碳酸盐岩中含有的烃类是原生的,还是它处运移充填而来的,这在勘探实践中具有不同的指导意义,本文阐述了用岩石热解分析技术判别碳酸盐岩中烃源的方法。提出了碳酸盐岩含油判别指数P、岩石热解烃最高温度Tmax和岩石中游离烃S1含量等判别碳酸盐岩是否含运移烃的指标。用此方法研究了西藏措勤盆地碳酸盐岩含油显示,发现强龙松纳背斜在1805剖面下白垩统郎山组1段(K1l^1)碳酸盐岩曾有油气运移过程存在。同时用其它方法证明了岩石热解技术对碳酸盐岩含运移烃的识别是可靠的。 相似文献
995.
996.
在线路施工的补充测量控制中,对先期控制点老坐标的如何使用,关系到新坐标的网形精度和与老坐标的差异程度.介绍了对先期控制点坐标进行赋权参加平差的方法,并给出评定结果的指标.用实例分析验证了这种方法的有效性. 相似文献
997.
Integrated Sensible Heat Flux Measurements of a Two-Surface Composite Landscape using Scintillometry 总被引:1,自引:0,他引:1
J.-P. Lagouarde J.-M. Bonnefond Y. H. Kerr K. J. McAneney M. Irvine 《Boundary-Layer Meteorology》2002,105(1):5-35
The potential of the LAS (large aperture scintillometry) method for measuring sensible heat flux (H) directly integrated over a two-field composite surface is evaluated. We describe a field experiment performed within the Alpilles/ReSeDa project in the south-east of France over a composite surface made up of wheat and bare soil (451 and 216 m long respectively) using two 0.15-m diameter scintillometers mounted at heights of 2.05 and 4.54 m. When compared against reference values obtained by the eddy correlation technique, LAS-measured sensible heat flux reveals a systematic overestimation of about 10%. A simple model describing the integration of the scintillometer signal along the beam for a two-field composite surface is described. A simulation of the experiment confirms that the bias observed isrelated to non-linearities in the integration process in relation with thebell-shape sensitivity curve of the instrument to the structure parameter for the refractive index it measures. The model is used to test the sensitivity of the LAS-derived H values to the composition of the pathlength (ratio of both surfaces) and to the contrast in sensible heat flux and roughness length between the two fields. Sensitivity tests to the aggregation scheme for roughness length (two of them are tested) and to the measurement height are also presented. The composition of the surface in combination with the contrast in sensible heat flux (in direct relation with the contrast in latent heat flux) explains most of the bias, with possible deviations ranging from -50 up to 80 W m-2. A tentative semi-empirical method for correcting the bias is suggested, which only requires a crude estimate of the contrast in component sensible heat fluxes along the pathlength. 相似文献
998.
New evidence for a relation between wind stress and wave age from measurements during ASGAMAGE 总被引:7,自引:0,他引:7
Data from the 1996 ASGAMAGE experiment, performed in the southern North Sea at research platform Meetpost Noordwijk (MPN), are analysed for the parameters affecting the momentum flux. The stress turns out to be quadratically related to the 10-m wind speed and linearly to the wind speed at a wavelength related level. The Charnock parameter (dimensionless roughness length) shows a pronounced correlation with wave age. This implies, due to a coupling between wave age and the steepness of the waves, a connection between the stress and the steepness. We find that our North Sea results are consistent withopen ocean observations. For a given wind speed the mean stress at MPN turns out to be higher because the wave age there is in general lower. We define and give an expression for a drag coefficient at a wavelength related level that can be calculated straightforwardly from the wave age and then reduced to a standard level. 相似文献
999.
滑动屋盖摩擦控制系统对地震频谱和结构刚度的鲁棒性 总被引:1,自引:0,他引:1
地震功率谱密度函数的频率范围和结构刚度变化对滑动屋盖摩擦控制系统减震效果的影响分析表明 :控制系统减震效果对地震功率谱的频域宽窄不敏感 ,而对功率谱所覆盖的结构自振频率敏感 ;结构刚度发生± 15 %的变化对减震效果的影响不大。分析还表明 ,滑动屋盖摩擦控制系统对于结构非线性地震反应有显著的减震作用 相似文献
1000.
应用广东数字遥测地震台网的数字化的地震形资料,研究阳江地震前,地震波波形时间线性度、平均半周期和地震波波形空间线性度等地震波参数变化特征。结果表明,震前半年时间内,上述地震波参数不同程度地出现下降异常。利用线性偏振度自动检测的P、S波初至具有可靠的精度,为广泛利用地震波参数预报地震提供了方便。 相似文献