A methodology for dynamic analysis of linear structure-foundation systems with local non-linearities     

Adnan Ibrahimbegovic  Edward L. Wilson 《地震工程与结构动力学》1990,19(8):1197-1208

An efficient computational technique is presented for the dynamic analysis of large linear structural systems with local non-linearities. The earthquake response evaluation for many practical structures belongs to this class of problems. The technique provides a rational approach to the earthquake-resistant design of structure-foundation systems with predetermined non-linearities occurring along the structure-foundation interface. Various possibilities for base isolation systems are naturally fitted within the proposed framework. In particular, we address uplifting of the structure as a natural base isolation concept. We use the dynamic substructuring technique and an efficient numerical algorithm which accommodates non-proportional damping as a consistent way to reduce significantly the computational effort, which is in sharp contrast to the vast majority of ad-hoc simplified models used for the same purpose. A numerical example which demonstrates the vibration isolation effect when the uplifting of the concrete gravity dam occurs is also presented.  相似文献   

High integrated fluid/rock ratios during metamorphism at Naxos: evidence from carbon isotopes of calcite in schists and fluid inclusions   总被引：3，自引：0，他引：3  

Rob Kreulen 《Contributions to Mineralogy and Petrology》1988,98(1):28-32

Calcite in schists of the metamorphic complex at Naxos is depleted both in ¹³C and in ¹⁸O with respect to massive marbles. This effect is attributed to isotope exchange with circulating CO₂-rich fluids, which had an >0.5 according to fluid inclusions. The carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion CO₂ at metamorphic temperatures. Mass balance calculations assuming initial ¹³C values of 0 for calcite and –5 for the fluid, give integrated fluid/rock volume ratios between 0.1 and 2.0. Such high fluid/rock ratios are supported by observations on the distribution of CO₂/H₂O ratios of fluid inclusions, carbon isotopic compositions of fluid inclusion CO₂ and oxygen isotope systematics of silicates.  相似文献   

Comments on a relationship between fluid and immersed-particle velocity fluctuations proposed by Walklate (1987)     

J. D. Wilson  E. P. Lozowski  Y. Zhuang 《Boundary-Layer Meteorology》1988,43(1-2):93-98

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The influence of geometry on the ascent of magma in open fissures   总被引：1，自引：0，他引：1  

G Giberti  L Wilson 《Bulletin of Volcanology》1990,52(7):515-521

During steady eruption, the flow conditions (emitted mass flux, exit velocity and exit pressure) depend on the geometry of the conduit in which the eruption occurs. This dependence is examined for the onedimensional, isothermal ascent of a homogeneous basaltic magma with an aqueous volatile phase and newtonian rheology. By fixing the geometry of the feeding fissure, the mass flux flowing in steady conditions can be determined at any depth, as well the magma pressure and vertical velocity. Flow behaviour is analysed for three fissure shapes: constant width, slowly upward narrowing and lenticular. In all the cases examined the magma arrives at the earth's surface with a pressure greater than atmospheric. The results are compared with those obtained when a lithostatic pressure gradient is assumed for the magma column. Some speculations are made, moreover, about the change in eruption style, if conduit geometry varies during a non-steady phase.  相似文献   

The Ground Water Recharge and Pollution Potential of Dry Wells in Pima County, Arizona     

L.G. Wilson  M.D. Osborn  K.L. Olson  S.M. Maida  L.T. Katz 《Ground Water Monitoring & Remediation》1990,10(3):114-121

This paper summarizes a study to estimate the potential for dry-well drainage of urban runoff to recharge and pollute ground water in Tucson, Arizona. We selected three candidate dry wells for study. At each site we collected samples of runoff, dry-well sediment, vadose-zone sediment, perched ground water, and ground water. Water content data from vadose-zone samples suggest that dry-well drainage has created a transmission zone for water movement at each site. Volatile organic compounds, while undetected in runoff samples, were present in dry-well sediment, perched ground water at one site, and ground water at two sites. The concentrations of volatile organics (toluene and ethylbenzene) in the water samples were less than the corresponding EPA human health criteria. Pesticides were detected only in runoff and dry-well sediment. Lead and chromium occurred in runoff samples at concentrations above drinking water standards. Nickel, chromium, and zinc concentrations were elevated in vadose-zone samples at the commercial site. Of the metals, only manganese, detected at the residential site, exceeded Secondary Drinking Water Standards in ground water. It is concluded that the three dry wells examined during this study are currently not a major source of ground water pollution.  相似文献   

Experience from one year of operating a boundary-layer profiler in the center of a large city     

R. R. Rogers  S. A. Cohn  W. L. Ecklund  J. S. Wilson  D. A. Carter 《Annales Geophysicae》1994,12(6):529-540

Since May 1992 a small, 915-MHz profiler has been operated continuously in downtown Montreal. It is a five-beam system employing a microstrip array antenna, located atop a 14-story office building that houses several academic departments of McGill University. The data are used for research on precipitation physics and the clear-air reflectivity in addition to wind profiling. We are especially interested in situations in which the reflectivities of the clear air and the precipitation are comparable. This permits the study of interactions between the precipitation and the clear air, a new area of research made possible by wind profilers. On clear days in the summer, 30-min consensus winds can often be measured to an altitude of 3 km, but ground clutter in the antenna sidelobes interferes with measurements below 600 m. Rain when present often permits wind profiling down to 100 m and up to 6 km or higher. On cold winter days there are some periods when the reflectivity is too weak at all levels to permit wind estimation. Falling snow, however, provides readily detectable echoes and serves as a good tracer of the wind and so allows profiling over its full altitude extent. The best conditions for observing interactions between precipitation and the clear air are when light rain falls through a reflective layer associated with a frontal surface or inversion. Unexpectedly, flocks of migrating birds sometimes completely dominate the signal at night in the spring and fall seasons.  相似文献   

Tectonic transition from the Songpan-Garzê Fold Belt to the Sichuan Basin, south-western China   总被引：1，自引：0，他引：1  

SHE FA Chen  CHRISTOPHER J. L. Wilson  BRENTON A. Worley 《Basin Research》1995,7(3):235-253

The formation of the Songpan-Garzê Fold Belt and the initiation of the terrestrial Sichuan Basin are related to closing of the Palaeo-Tethys during the Late Triassic Indosinian orogeny. The Songpan-Garzê Fold Belt is composed of Triassic (T₁-_-T²₃) turbiditic deposits and Palaeozoic greywacke-shale, whereas the Sichuan Basin consists of Sinian to middle Upper Triassic (T²₃) platform carbonates and Upper Triassic (T_3X to Quaternary terrestrial elastics. Three principal deformation episodes during the Late Triassic (Norian to Rhaetian) were progressively localized towards the south-eastern margin of the fold belt. D₁ was a SW-directed shortening event, related to continuous subduction of the Palaeo-Tethys, and produced NW-trending structures. Differential strain between the fold belt and the Sichuan Basin was accommodated by sinistral shearing along a NE-trending transitional zone during D₂^. D₃ SE-directed compression was the result of collision between the Cimmerian and Eurasian Continents and initiated the Longmen Mountains Thrust-Nappe Belt and terrestrial Sichuan Basin. Post-D₃ deformation, related to SE-directed thrusting in the Longmen Mountains, then propagated from hinterland to foreland. The Indosinian orogeny closed the Palaeo-Tethys and terminated the marine conditions that dominated the early evolution of the intracratonic Sichuan Basin. Tectonic loading from the exhumed fold belt and Thrust-Nappe Belt induced substantial subsidence in the Sichuan Basin, especially in the Western Sichuan Foreland Basin, resulting in the deposition of a terrestrial clastic sequence during Late Triassic (T_3X to Quaternary times. The foreland basin history comprises an early stage during the Late Triassic (T_3x^1–2), an over-fill stage during the latest Triassic to Early Cretaceous (T_3X³- K_1J), and a shrinking stage from the Late Cretaceous to the Quaternary (K_2J-Q). These can be correlated with tectonic events in the Thrust-Nappe Belt.  相似文献   

Explosive volcanic eruptions—VIII. The role of magma recycling in controlling the behaviour of Hawaiian-style lava fountains     

L. Wilson  E. A. Parfitt  J. W. Head III 《Geophysical Journal International》1995,121(1):215-225

Explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma, its erupted mass flux, and the geometry of the vent (which may be an elongate fissure or a localized, near-circular conduit). The geometry of the initial vent (and the eruptive behaviour) can be distinctly modified by lava drainback and accumulating ejecta. Hot pyroclasts landing near the vent may coalesce to form rootless flows, some of which may drain back into the vent to be recycled into the eruption products. Rootless flows may be at least partially confined by pre-existing topographic features, or by spatter or cinder ramparts being built up by the eruption itself, so that they accumulate into a lava pond over and around the vent. The erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so. The energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth (or lava drainback rate). The results of such calculations are presented, and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights.  相似文献   

A paleomagnetic reinvestigation of the Upper Devonian Perry Formation: evidence for Late Paleozoic remagnetization     

Carola Stearns  Rob Van der Voo 《Earth and Planetary Science Letters》1987,86(1)

In view of the recent recognition of widespread Late Paleozoic remagnetization of Devonian formations across North America, we undertook a reinvestigation of the Upper Devonian Perry Formation of coastal Maine and adjacent New Brunswick. Thermal demagnetization of samples from the redbeds yielded a characteristic direction (D = 166°, I = 4°) that fails a fold test. Comparison of the corresponding paleopole (312°E, 41°S) with previously published Paleozoic poles for North America suggests that the sediments were remagnetized in the Late Carboniferous. After the removal of a steep, northerly component, the volcanics also reveal a shallow and southerly direction ( D = 171°, I = 25° without tilt correction). No stability test is available to date the magnetization of the volcanics; however, similarity of several of the directions to those seen in the sediments raises the suspicion that the volcanics are also remagnetized. Although the paleopole without tilt correction (303°E, 32°S) could be taken to indicate an early Carboniferous age for the remagnetization, scatter in the data suggests that the directions are contaminated by the incomplete removal of a steeper component due to present-day field. Thus, it is more likely that the volcanics were remagnetized at the same time as the sediments. Isothermal remanent magnetization (IRM) acquisition curves, blocking temperatures, coercivities and reflected light microscopy indicate that the magnetization is carried by hematite in the sediments and by both magnetite and hematite in the volcanics. It is therefore likely that the remagnetization of the Perry Formation involved both thermal and chemical processes related to the Variscan/Alleghenian orogeny. Our results indicate that previously published directions for the Perry Formation were based on the incomplete resolution of two magnetic components. These earlier results can no longer be considered as representative of the Devonian geomagnetic field.  相似文献   

On the choice of a windbreak porosity profile     

J. D. Wilson 《Boundary-Layer Meteorology》1987,38(1-2):37-49

Measurements of mean windspeed and turbulence were carried out behind two sections of 50% porous fence differing only in the vertical distribution of their porosity. One section of the fence was uniformly porous, the other relatively dense near the ground and open aloft. Slightly greater mean speed reduction was observed near the ground in the near lee of the section which was dense at ground-level without any detrimental increase in turbulence. However, this advantage was offset by less effective protection in the far lee. These findings are consistent with earlier work by Gandemer (1979) and with the predictions of a numerical model of windbreak flow.  相似文献