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151.
The notion of Hill stability is extended from the circular restricted 3-body problem to the general three-body problem; it is even extended to systems of positive energy and the Hill's curves with their corresponding forbidden zones are generalized.Hill stable systems of negative energy present a hierarchy: they have a close binary that can be neither approached nor disrupted by the third body. This phenomenon becomes particularly clear with the distance curves presentation.The three limiting cases, restricted, planetary and lunar are analysed as well as some real stellar cases. 相似文献
152.
George Bozis 《Astrophysics and Space Science》1976,43(2):355-368
The angular momentum and the energy integral of the planar three-body problem are used to establish regions of the physical space where motion is allowed to take place. Although forbidden regions exist for both negative and positive values of the energy of the system, the known integrals of the motion always allow for at least one of the three bodies to escape. 相似文献
153.
Soil effects on peak ground acceleration, velocity and elastic response spectra (5% damping) are expressed by simple approximate relations in terms of five key parameters: (a) the fundamental vibration period of the non‐linear soil, TS, (b) the period of a bedrock site of equal thickness, Tb, (c) the predominant excitation period, Te, (d) the peak seismic acceleration at outcropping bedrock, a, and (e) the number of significant excitation cycles, n. Furthermore, another relation is proposed for the estimation of TS in terms of the soil thickness H, the average shear wave velocity of the soil V?S,o and a. The aforementioned parameters were first identified through a simplified analytical simulation of the site excitation. The multivariable approximate relations were then formulated via a statistical analysis of relevant data from more than 700 one‐dimensional equivalent‐linear seismic ground response analyses, for actual seismic excitations and natural soil conditions. Use of these relations to back‐calculate the numerical results in the database gives an estimate of their error margin, which is found to be relatively small and unbiased. The proposed relations are also independently verified through a detailed comparison with strong motion recordings from seven well‐documented case studies: (a) two sites in the San Fernando valley during the Northridge earthquake, and (b) five different seismic events recorded at the SMART‐1 accelerometer array in Taiwan. It is deduced that the accuracy of the relations is comparable to that of the equivalent‐linear method. Hence, they can be readily used as a quick alternative for routine applications, as well as for spreadsheet computations (e.g. GIS‐aided seismic microzonation studies) where numerical methods are cumbersome to implement. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
154.
Djuro Novakovic Christopher D. White Rucsandra M. Corbeanu William S. Hammon III Janok P. Bhattacharya George A. McMechan 《Mathematical Geology》2002,34(7):857-893
Ground-penetrating radar (GPR) surveys, outcrop measurements, and cores provide a high-resolution 3D geologic model to investigate the hydraulic effects of shales in marine-influenced lower delta-plain distributary channel deposits within the Cretaceous-age Ferron Sandstone at Corbula Gulch in central Utah, USA. Shale statistics are computed from outcrop observations. Although slight anisotropy was observed in mean length and variogram ranges parallel and perpendicular to pale of low
, the anisotropy is not statistically significant and the estimated mean length is 5.4 m. Truncated Gaussian simulation was used to create maps of shales that are placed on variably dipping stratigraphic surfaces interpreted from high-resolution 3D GPR surveys, outcrop interpretations, and boreholes. Sandstone permeability is estimated from radar responses calibrated to permeability measurements from core samples. Experimentally designed flow simulations examine the effects of variogram range, shale coverage fraction, and trends in shale coverage on predicted upscaled permeability, breakthrough time, and sweep efficiency. Approximately 1500 flow simulations examine three different geologic models, flow in the 3 coordinate directions, 16 geostatistical parameter combinations, and 10 realizations for each model. ANOVA and response models computed from the flow simulations demonstrate that shales decrease sweep, recovery, and permeability, especially in the vertical direction. The effect on horizontal flow is smaller. Flow predictions for ideal tracer displacements at Corbula Gulch are sensitive to shale-coverage fraction, but are relatively insensitive to twofold variations in variogram range or to vertical trends in shale coverage. Although the hydraulic effects of shale are statistically significant, the changes in flow responses rarely exceed 20%. As a result, it may be reasonable to use simple models when incorporating analogous shales into models of reservoirs or aquifers. 相似文献
155.
George MillwardSteve Miller Tom StallardAlan D. Aylward Nicholas Achilleos 《Icarus》2002,160(1):95-107
Recent work has been concerned with calculating the three-dimensional ion concentrations and Pedersen and Hall conductivities within the auroral region of Jupiter for varying conditions of incident electron precipitation. Using the jovian ionospheric model, we present results that show the auroral ionospheric response to changing the incoming flux of precipitating electrons (for constant initial energy) and also the response to changing the initial energy (for both constant flux and constant energy flux). The results show that, for expected energy fluxes of precipitating particles, the average auroral integrated Pedersen conductivity attains values in excess of 1 mho. In addition, it is shown that electrons with an initial energy of around 60 keV are particularly effective at generating auroral conductivity: Particles of this energy penetrate most effectively to the layer of the jovian ionosphere at which the auroral conductivity is at a maximum. 相似文献
156.
Volume Contents
Contents to Volume 8 相似文献157.
Numerical and analytical solutions are presented for the elastic and inelastic response of single‐degree‐of‐freedom yielding oscillators to idealized ground acceleration pulses. These motions are typical of near‐fault earthquake recordings generated by forward rupture directivity and may inflict damage in the absence of substantial structural strength and ductility capacity. Four basic pulse waveforms are examined: (1) triangular; (2) sinusoidal; (3) exponential; and (4) rectangular. In the first part of the article, a numerical study is presented of the effect of oscillator period, strength, damping, post‐yielding stiffness and number of excitation cycles, on inelastic response. Results are presented in the form of dimensionless graphs and regression formulas that elucidate the salient features of the problem. It is shown that conventional R–µ relations may significantly underestimate ductility demand imposed by near‐fault motions. The second part of the article concentrates on elastic‐perfectly plastic oscillators. Closed‐form solutions are derived for post‐yielding response and associated ductility demand. It is shown that all three ground motion histories (i.e. acceleration, velocity, and displacement) control oscillator response—contrary to the widespread view that ground velocity alone is of leading importance. The derived solutions provide insight on the physics of inelastic response, which is often obscured by the complexity of numerical algorithms and actual earthquake motions. The model is evaluated against numerical results from near‐field recordings. A case study is presented. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
158.
3-D shell analysis of cylindrical underground structures under seismic shear (S) wave action 总被引:1,自引:1,他引:1
George P. Kouretzis George D. Bouckovalas Charis J. Gantes 《Soil Dynamics and Earthquake Engineering》2006,26(10):909-921
The 3-D shell theory is employed in order to provide a new perspective to earthquake-induced strains in long cylindrical underground structures, when soil-structure interaction can be ignored. In this way, it is possible to derive analytical expressions for the distribution along the cross-section of axial, hoop and shear strains and also proceed to their consistent superposition in order to obtain the corresponding principal and von Mises strains. The resulting analytical solutions are verified against the results of 3-D dynamic FEM analyses. Seismic design strains are consequently established after optimization of the analytical solutions against the random angles which define the direction of wave propagation relative to the longitudinal structure axis, the direction of particle motion and the location on the structure cross-section. The basic approach is demonstrated herein for harmonic shear (S) waves with plane front, propagating in a homogeneous half-space or in a two layer profile, where soft soil overlays the bedrock. 相似文献
159.
At times of strong solar wind forcing such as those that produce major magnetic storms, the region 1 current system dominates over the Chapman–Ferraro current system in mediating the transfer of force between the solar wind and the terrestrial system. The global force balance can be broken into two components, one involving the high-altitude part of the region 1 current system that is in contact with the solar wind (labeled here the HRS) and the other involving the low-altitude part of the region 1 current system that lies in the ionosphere (the LRS). Both communicate their J×B force to the geomagnetic dipole via a gradient in the magnetic field that they generate. In the HRS case the force acts to push the dipole away from the sun. This is the region 1 analog of the Chapman–Ferraro mechanism for transmitting the solar wind's force to the Earth. However, in the LRS case, the force (which is much stronger than in the HRS case) acts to push the dipole toward the sun, seemingly paradoxically. The LRS balances the ‘paradoxical’ sunward force on the dipole with an opposite force on the atmosphere. This paper uses MHD simulations to demonstrate the presence of both the normal force-transmitting gradient generated by the Chapman–Ferraro and the counter-Chapman–Ferraro gradient in the magnetic field generated by the region 1 current system. 相似文献
160.
George Helffrich 《Astronomy& Geophysics》2006,47(1):1.20-1.26
George Helffrich discusses the links between seismology and geochemistry in the Bullerwell Lecture 2005, delivered at the annual meeting of the European Union of Geosciences in Vienna. 相似文献