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61.
World-wide synthetic tide parameters for gravity and vertical and horizontal displacements 总被引:3,自引:0,他引:3
The response of the Earth’s crust to the direct effect of lunisolar gravitational forcing is known as the body tide. The body tide is superimposed by surface-loading forces due to the pressure of the periodically varying ocean tide acting on the Earth, called ocean tide loading (OTL). Both body tide and OTL can be decomposed into components of the same frequency known as tidal parameters. However, OTL is more complicated than body tides because of the dynamic effects of the ocean. Estimating OTL requires a model of the ocean tides and knowledge of the elastic properties of the solid Earth. Thus, synthetic tide parameters (amplitude factors and phase leads) have been developed here on a world-wide grid for gravity and positional displacements. The body tide contributions were added to the oceanic contribution to provide the Earth tide response. The accuracy and reliability of the synthetic tidal parameters have been estimated by comparing observed gravity and vertical-displacement tide parameters with those interpolated from our synthetic model, which shows good agreement. Tests also indicate that the synthetic tide parameters provide realistic gravimetric and displacements for practical use in tidal prediction. 相似文献
62.
Chunxiang Li 《地震工程与结构动力学》2002,31(4):897-919
Multiple tuned mass dampers (MTMD) consisting of many tuned mass dampers (TMDs) with a uniform distribution of natural frequencies are taken into consideration for attenuating undesirable vibration of a structure under the ground acceleration. A study is conducted to search for the preferable MTMD which performs better and is easily manufactured from the five available models (i.e. MTMD‐1 – MTMD‐5), which comprise various combinations of the stiffness, mass, damping coefficient and damping ratio in the MTMD. The major objective of the present study then is to evaluate and compare the control performance of these five models. The structure is represented by its mode‐generalized system in the specific vibration mode being controlled by adopting the mode reduced‐order approach. The optimum parameters of the MTMD‐1 – MTMD‐5 are investigated to reveal the influence of the important parameters on their effectiveness and robustness using a numerical searching technique. The parameters include the frequency spacing, average damping ratio, tuning frequency ratio, mass ratio and total number. The criteria selected for the optimum searching are the minimization of the maximum value of the displacement dynamic magnification factor (DDMF) and that of the acceleration dynamic magnification factor (ADMF) of the structure with the MTMD‐1 – MTMD‐5 (i.e. Min.Max.DDMF and Min.Max.ADMF). It is demonstrated that the optimum MTMD‐1 and MTMD‐4 yield approximately the same control performance, and offer higher effectiveness and robustness than the optimum MTMD‐2, MTMD‐3, and MTMD‐5 in reducing the displacement and acceleration responses of structures. It is further demonstrated that for both the best effectiveness and robustness and the simplest manufacturing, it is preferable to select the optimum MTMD‐1. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
63.
The damping‐solvent extraction method for the analysis of unbounded visco‐elastic media is evaluated numerically in the frequency domain in order to investigate the influence of the computational parameters—domain size, amount of artificial damping, and mesh density—on the accuracy of results. An analytical estimate of this influence is presented, and specific questions regarding the influence of the parameters on the results are answered using the analytical estimate and numerical results for two classical problems: the rigid strip and rigid disc footings on a visco‐elastic half‐space with constant hysteretic material damping. As the domain size is increased, the results become more accurate only at lower frequencies, but are essentially unaffected at higher frequencies. Choosing the domain size to ensure that the static stiffness is computed accurately leads to an unnecessarily large domain for analysis at higher frequencies. The results improve by increasing artificial damping but at a slower rate as the total (material plus artificial) damping ratio ζt gets closer to 0.866. However, the results do not deteriorate significantly for the larger amounts of artificial damping, suggesting that ζt≈0.6 is appropriate; a larger value is not likely to influence the accuracy of results. Presented results do not support the earlier suggestion that similar accuracy can be achieved by a large bounded domain with small damping or by a small domain with larger damping. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
64.
X射线衍射峰五基本要素的物理学意义与应用 总被引:6,自引:0,他引:6
本文根据Bragg衍射方程、Scherrer方程、衍射强度计算原理,研究讨论了X射线衍射5构成要素中的衍射峰位置、衍射峰宽度、衍射峰高度的物理学意义。根据实验研究证明了衍射峰不对称性的几何条件特征,并用地质事实验证了衍射形态变化与晶格应变和粒度大小的内在联系。从而阐明了单个衍射峰5基本构成要素的完整物理学意义,并以实例论证了5要素的实际应用价值。 相似文献
65.
Uniform models for the Earth–ionosphere cavity are considered with particular attention to the physical properties of the ionosphere for the extremely low frequency (ELF) range. Two consistent features have long been recognized for the range: the presence of two distinct altitude layers of maximum energy dissipation within the lower ionosphere, and a “knee”-like change in the vertical conductivity profile representing a transition in dominance from ion-dominated to electron-dominated conductivity. A simplified two-exponential version of the Greifinger and Greifinger (1978) technique widely used in ELF work identifies two slopes in the conductivity profile and, providing accurate results in the ELF communication band (45–75 Hz), simulates too flat a frequency dependence of the quality factor within the Schumann resonance frequency range (5–40 Hz). The problem is traced to the upward migration, with frequency increasing, of the lower dissipation layer through the “knee” region resulting in a pronounced decrease of the effective scale height for conductivity. To overcome this shortcoming of the two-exponential approximation and still retain valuable model analyticity, a more general approach (but still based on the Greifinger and Greifinger formalism) is presented in the form of a “knee” model whose predictions for the modal frequencies, the wave phase velocities and the quality factors reasonably represent observations in the Schumann resonance frequency range. 相似文献
66.
大型维歇特地震仪自德国引进南京地震台已近70年。本文简要叙述了该仪器的性能;并以南京地震台的大型维歇特地震仪的记录为例,介绍了该仪器在300-2000km范围内的记录特征,回顾了该仪器在地震速报中所起的历史作用。 相似文献
67.
Study of the Earth’s free core nutation by tidal gravity data recorded with international superconducting gravimeters 总被引:2,自引:0,他引:2
By stacking high-precision tidal gravity observations obtained with superconducting gravimeters at six stations in China,
Japan, Belgium, France, Germany and Finland, the local systematical discrepancies in the parameter fitting, caused by atmospheric,
oceanic tidal loading and the other local environmental perturbations, are eliminated effectively. As a result, the resonance
parameters of the Earth’s free core nutation are accurately determined. In this study, the eigenperiod of free core nutation
is given as 429.0 sidereal days, which is in agreement with those published in the previous studies. It is about 30 sidereal
days less than those calculated in theoretical models (about 460 sidereal days), which confirms the real ellipticity of the
fluid core of the Earth to be about 5% larger than the one expected in assumption of hydrostatic equilibrium. The quality
factor (Q value) of free core nutation is given as about 9543, which, compared with those determined before based on the body
tide observations, is much larger, but more close to those obtained using the VLBI observations. The complex resonance strength
is also determined as (−6.10×10−4, −0.01 ×10−4)°/h, which can principally describe the deformation characteristics of an anelastic mantle. 相似文献
68.
山东月湖的沉积物分布特征及搬运趋势 总被引:12,自引:0,他引:12
1998年 11~ 12月和 1999年 8~ 9月各一个月对月湖进行的野外工作 ,共取得表层沉积物样品 131个 ,应用激光粒度仪并结合传统的筛分法对这些样品进行粒度分析 ,进行矩法计算获得粒度参数。采用Gao命名方法 ,将沉积物划分出 5种主要类型。利用Gao -Collins粒径趋势分析模型 ,计算该区沉积物粒径趋势所显示的沉积物净搬运方向 ,结果表明 ,沉积物从四周向湖中心搬运 ,同时显示湾顶的西部和北部、涨潮三角洲以及湖心等地貌单元是沉积的优势区域。 相似文献
69.
The groundwater table has been declining at a rate of 0.65 m/yr in Luancheng County since large scale groundwater extraction
carried out in the 1960s. The drop of precipitation, substantial increase in agricultural output, variations of crop planting
structure and construction of water conservancy projects in the headwater area all tie up with the decline of the groundwater
table. On the basis of analyzing the hydrogeological conditions and the water resources utilization of Luancheng County, a
three-dimensional groundwater flow model was developed to simulate the county’s groundwater flow through finite-difference
method using Visual Modflow software. We divide the research field into four parts after analyzing the hydrogeological condition.
Based on parameter calibration and adjustment using measured data, the hydraulic conductivity and specific yield were simulated.
Using the calibrated model, we analyze the agricultural water saving potentiality and its influence on the groundwater. The
results are as follows: (1) if we decrease the amount of water extracted by 0.14xl08 m3, the average groundwater table of the five observation wells in December will rise by 0.33 m; (2) if we decrease the water
by 0.29x 108m3, the average groundwater table of the five observation wells in December will rise by 0.64 m; and (3) if we increase the
water by 0.29 x 108m3, the average groundwater table of the five observation wells in December will decline by 0.45 m. So we can draw a conclusion
that controlling the agricultural water use is an important way to prevent the decline of groundwater table. 相似文献
70.
Source scaling of intermediate-depth Vrancea earthquakes 总被引:3,自引:0,他引:3