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1.
Summary The paper deals with the solving of large systems of linear equations which are created when implicit and semi-implicit differential methods are used to solve the primitive equations of the atmosphere. Systems with similar properties are also created in solving boundary problems of multi-level filtered models. First, the specific properties of these systems, which are then used to construct an efficient method of solving them, are described. 相似文献
2.
This paper presents a two-dimensional numerical study on the nonlinear seismic response of buildings equipped with two types of energy dissipators: Constant Friction Slip Braces (CFSB) and Adding Damping and Stiffness (ADAS). Three types of reinforced concrete buildings with 3, 7 and 15 storeys, representatives of the short-medium- and long-period ranges, are considered. Dissipators are placed in steel diagonal braces in all the floors. The sliding threshold (or yielding) forces for each mechanism are selected using two different criteria: (i) they are taken as 50, 75 and 100 per cent of those generated by the equivalent static lateral forces recommended by the UBC-91 for a ductile moment resisting frame and (ii) they are constant in the whole building (this constant value is chosen equal to the maximum forces obtained with the previous criterion). The input consists of ten recorded earthquakes (normalized with respect to their Housner intensity) corresponding to medium and stiff local soil conditions. Average values on the ten registers are given for the maximum horizontal displacement, the base shear, the energy dissipated and the interstorey drift. The possibility of failure in some devices has been numerically simulated to assess the robustness of the system. The obtained results show that both devices are useful to reduce the response compared to the bare frame and that CFSB is more efficient than ADAS; for 7- and 15-storey frames the lateral displacement with CFSB is even smaller than the one for the braced frame (rigid connections instead of dissipators). The conclusions are expected to provide simple design guidelines. © 1998 John Wiley & Sons, Ltd. 相似文献
3.
The Deccan Trap basalts have long been considered to be products of fissure eruptions and the dykes intruding them have been supposed to represent the fissures of eruption. However, the question of the mode of eruption of Deccan Trap lavas seems to need more careful consideration in view of the features brought to light by detailed field work in Western Maharashtra. Detailed studies of dykes suggest that majority of the dykes could not have acted as feeders as previously supposed. When examined in detail the basalt flows have more often been found to have only a limited lateral extent and are not always quite horizontal. Thin irregular flows with ropy surfaces, dipping in different directions and piled up into a chaotic mass are frequently met with, indicating eruption from local vents of the central type. Volcanic vents are found at a number of widely separated localities. All this suggests that many lavas are products of central type of volcanicity. However, central type of volcanoes would be inadequate to account for the vast amounts of lavas, and as the known dykes are not likely to have acted as feeders, and dykes still remain to be reported from large portions of the Deccan Trap area, the question of how the lavas came to the surface largely remains unanswered. Extensive beds of volcanic breccia traceable over a few miles and upto 50 feet thick are met with. As such extensive beds are more likely to be associated with fissure cruptions the question arises whether these fissure eruptions were accompanied by considerable explosive activity. 相似文献
4.
Reflection and refraction of plane wave through an interface between fluid and rock with elastic deformations on the basis of the acoustoelastic theory are considered. The effects of stress on the anisotropy and energy reflection and transmission coefficients are investigated. The incident wave plane can coincide with or deviate from planes of material symmetry. Elastic deformations are assumed to be locally homogeneous and to satisfy static boundary conditions. Numerical computations are carried out and comparisons are made with the results predicted in the presence and absence of initial stress. The changes in phase velocity, group velocity, and energy reflection and refraction coefficients due to the presence of stress are displayed graphically and discussed. The results show that the effect of stress depends on its magnitude, direction and form (uniaxial and biaxial). 相似文献
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K. Rinner 《Surveys in Geophysics》1974,1(4):459-479
Distance measurement with the aid of electromagnetic waves permits the determination of sides of any length with an accuracy equal or superior to that of a base length plus angular measurements. In conjunction with the automation of measurement and calculation, geodesy is now able to determine quickly and with high accuracy positions on the Earth's surface, and of objects on the surface or in outer space. Therefore, these procedures are of high importance to all geosciences.The theoretical fundamentals of the measuring procedures are described first. The form of the path curve and the determination of a representative wave velocity along this path curve are dealt with. The principles of the measuring instruments are explained, and a survey is given of the electro-optic and microwave instruments now available. Possible applications of the measuring procedures in geodesy and other sciences are discussed and applications in use are described.An outlook is provided on the future development of geodetic procedures for which electromagnetic distance measurement will play an important part. 相似文献
7.
使用高灵敏度的电容式微压波传感器对1998年4月11日16时发生在贵州省普定县的一次降冰雹过程的重力波进行观测,利用WRF（Weather Research and Forecast）中尺度模式对这一过程进行数值模拟,使用Morlet小波方法对模拟结果进行分析,得出这一过程中惯性重力波的分布和变化规律,并分析急流、地形及切变线对惯性重力波的影响.观测发现：在降冰雹前,每隔1~4小时出现一次短周期重力波阵性增强的现象.数值模拟结果显示：在低空降冰雹前几个小时有强的短周期重力波出现,其中周期较长的出现早、存在时间长,周期较短的出现晚、存在时间短;强的低空急流和风速垂直切变触发对流或湍流的发生和加强,对流或湍流又激发了80~200 min的短周期重力波;短周期重力波更容易向垂直方向传播,而长周期重力波倾向于水平方向传播.长周期重力波在降冰雹后周期有明显变短现象,随高度越加明显.由地形形成的重力波在最高山峰上空振幅最大. 相似文献
8.
Sonia E. Ruiz 《地震工程与结构动力学》1991,20(1):1-9
Asymmetrically yielding single-degree-of-freedom elastoplastic systems are subjected to simulated accelerograms based on El Centro-NS, 1940 ground motion (wide frequency band) to calculate the corresponding ductility demands. Results are compared with those corresponding to simulated accelerograms of the SCT-EW, 1985 Mexico earthquake (narrow frequency band) obtained in a previous work. Results obtained reveal that the characteristics of the excitation influence the response of asymmetrically yielding structures and that the differences found on responses corresponding to both earthquakes are due to frequency content, duration and/or intensity of motion. The effect of the latter concepts is studied using modulating sinusoidal excitations as well as accelerograms recorded on soft and hard soils of Mexico City. Two alternate expressions are proposed to evaluate the increase in ductility demands of structures with asymmetric force-displacement curves with respect to symmetric ones. Those expressions take into account motion intensity and duration, as well as seismic design coefficient. 相似文献
9.
The Physics of Lightning 总被引：1，自引：0，他引：1
V. A. Rakov 《Surveys in Geophysics》2013,34(6):701-729
An overview of the physics of cloud-to-ground lightning is given, including its initiation, propagation, and attachment to ground. Discharges artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique are discussed with a view toward studying properties of natural lightning. Both conventional and runaway breakdown mechanisms of lightning initiation in thunderclouds are reviewed, as is the role of the lower positive charge region in facilitating different types of lightning. New observations of negative-leader stepping and its attachment to ground are compared to similar processes in long laboratory sparks. The mechanism and parameters of compact intracloud lightning discharges that are thought to be the most intense natural producers of HF-VHF (3–300 MHz) radiation on Earth are reviewed. The M-component mode of charge transfer to ground and its difference from the leader/return-stroke mode are discussed. Lightning interaction with the ionosphere and the production of energetic radiation (X-rays and gamma radiation) by cloud-to-ground leaders are considered. 相似文献
10.
Shear building representations of seismically isolated buildings 总被引：2，自引：0，他引：2
Seismic isolation, with its capability of reducing floor accelerations and interstory drifts simultaneously, is recognized
as an earthquake resistant design method that protects contents of a building along with the building itself. In research
studies, superstructures of seismically isolated buildings are commonly modeled as idealized shear buildings. Shear building
representation corresponds to an idealized structure where the beams are infinitely stiff in flexure and axially inextensible;
columns are axially inextensible; and rigid floors are supported on these columns. Although it is more convenient to model
and analyze a shear building, such an idealization may influence the seismic responses of seismically isolated buildings.
This study presents a comparison of the seismic performances of seismically isolated buildings with superstructures modeled
as shear buildings to those with full three dimensional superstructures. Both linear and nonlinear base isolation systems
with different isolation periods and superstructures with different number of stories are considered. 相似文献
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2014年山西定襄七岩泉新增BHC-336智能定标器,对新、旧2套测氡仪的水氡测值,就稳定性、数据一致性、内在质量等进行对比分析,结果显示,因存在系统误差,2台测氡仪水氡测值稳定性均值存在差异,测量精度和性能具有一致性;与新测氡仪相比,旧测氡仪水氡测值相对偏差和均值标准误差更小,精度更高,数据相关程度较高,数据稳定性更好。定襄水氡对华北5级以上地震具有较好的映震能力,新测氡仪对2016年4月7日原平4.6级地震映震效能比旧测氡仪灵敏。 相似文献
13.
J. M. Hooke 《地球表面变化过程与地形》1980,5(2):143-157
Measurements of bank erosion on rivers in Devon over a 2½ year period produced mean rates ranging from 0.08 to 1.18 metres per year and a maximum rate of 2.58 metres per year. These values are compared with rates derived from maps for various time periods between 1840 and 1975. The map rates are generally lower than the field rates and the question of whether this difference is due to the method of measurement, the magnitude-frequency of events, a change in discharge conditions or the inherent variation in channel activity is discussed. Published data on bank erosion rates are reviewed and the Devon rates are found to coincide with the worldwide distribution. An analysis of factors likely to influence the spatial distribution of erosion rates reveals a square-root relationship to catchment area and the importance of bank material. Implications of the measured rates for development of flood plains are examined. 相似文献
14.
The effectiveness of Tuned Mass Dampers (TMD) on buildings subjected to moderate and high-intensity motions is analysed. First, the response of a 22-storey four-bay reinforced concrete non-linear frame with a TMD is studied for motions with different intensities. Several values of the relevant parameters are assumed in the analyses. Then, equivalent single-degree-of-freedom systems with TMDs and without them are defined and analysed under the action of ground motions with intensities associated with different return intervals at the site where the structures are located. Vulnerability curves for the systems are obtained based on the probabilities of reaching two different performance limit states. The expected annual rate of exceedance of each limit state is calculated. The results show that the effectiveness of TMDs is higher for systems with small non-linearity produced by small and moderate earthquakes, than for systems with high non-linear behaviour, generally associated with high-intensity motions. Some recommendations about the applicability of TMD are given. Copyright © 1999 John Wiley & Sons Ltd. 相似文献
15.
This study focuses on the response of seismic isolated bridges subjected to near-field ground motions with distinct pulse type behavior in terms of maximum isolator displacements (MIDs) and maximum isolator forces (MIFs) transferred to the substructure. The employed isolation systems are composed of lead rubber bearings (LRBs) with bi-linear force-deformation relations that consider cycle-to-cycle deterioration in the yield strength of the LRBs due to heating of the lead core. MIDs and MIFs with due consideration of cycle-to-cycle deterioration are compared with that of non-deteriorating ones. Bounding analyses are also performed for comparison purposes. Nonlinear response history analyses are conducted with two bins of ground motions recorded at different soil conditions to investigate the effect of ground motion characteristics. Results indicate that MIDs are overestimated by lower bound analyses when seismic isolated bridges are subjected to near-field motions with high velocity pulses especially for the bearings with higher Q/W ratios. 相似文献
16.
De-yi Feng Jing-ping Gu Ming-zhou Lin Shao-xie Xu Xue-jun Yu 《Pure and Applied Geophysics》1984,122(6):982-997
A probabilistic method and a retrieval method of fuzzy information are simultaneously studied for assessment of earthquake hazard, or earthquake prediction. Statistical indices of regional seismicity in three adjacent time intervals are used to predict an earthquake in the next interval. The indices are earthquake frequency, the maximum magnitude, and a parameter related to the average magnitude (orb-value) and their time derivatives. Applying the probabilistic method, we can estimate a probability for a large earthquake with magnitude larger than a certain threshold occurring in the next time interval in a given region. By using the retrieval method of fuzzy information we can classify time intervals into several classes according to the regional seismic activity in each time interval and then evaluate whether or not the next time interval belongs to seismically hazardous time interval with a large earthquake. Some examples of applying both methods to the North section of the North-South Seismic Zone in China are shown. The results obtained are in good agreement with actual earthquake history. A comparison of the probabilistic method with the method of fuzzy mathematics is made, and it is recommended that earthquake hazard be assessed by simultaneous use of both methods. 相似文献
17.
K. N. Anakhaev 《Water Resources》2009,36(5):507-512
Semi-inverse method with successive conformal mapping are used to obtain a particular solution of the problem of steady-state flow of a groundwater mound. Groundwater flow parameters are evaluated, and examples of calculations are given. The obtained solutions coincide with available exact solutions in particular cases. 相似文献
18.
H. Lundstedt 《Surveys in Geophysics》1996,17(5):561-573
This review deals with how the changes of the large-scale solar magnetic fields are related to the occurrence of solar phenomena, which are associated with geomagnetic storms. The review also describes how artificial neural networks have been used to forecast geomagnetic storms either from daily solar input data or from hourly solar wind data. With solar data as input predictions 1–3 days or a month in advance are possible, while using solar wind data as input predictions about an hour in advance are possible. The predictions one hour ahead of the geomagnetic storm indexD
st
from only solar wind input data have reached such high accuracy, that they are of practical use in combination with real-time solar wind observations at L1. However, the predictions days and a month ahead need to be much improved in order to be of real practical use. 相似文献
19.
Abstract Non-Markovian closure theories are compared with ensemble averaged direct numerical simulations (DNS) for decaying two-dimensional turbulence at large scale Reynolds numbers ranging from ≈ 50 to ≈ 4000. The closures, as well as DNS, are formulated for discrete wave numbers relevant to flows on the doubly periodic domain and are compared with the results of continuous wave number closures. The direct interaction approximation (DIA), self-consistent field theory (SCFT) and local energy-transfer theory (LET) closures are also compared with cumulant update versions of these closures (CUDIA, CUSCFT, CULET). The cumulant update closures are shown to have comparable performance to the standard closures but are much more efficient allowing long time integrations. The discrete wave number closures perform considerably better than continuous wave number closures as far as evolved energy and transfer spectra and skewness are concerned. The discrete wave number closures are in reasonable agreement with DNS in the energy containing range of the large scales for Reynolds numbers ranging from ≈ 50 to ≈ 4000. The closures tend to underestimate the enstrophy flux to high wave numbers, increasingly so with increasing Reynolds number, resulting in underestimation of small-scale kinetic energy. 相似文献