Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law          下载免费PDF全文

Ahmad Hajjar  Luc Scholtès  Constantin Oltéan  Michel Antoine Buès 《水文研究》2018,32(16):2510-2525

Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls.  相似文献   

Relationship between pollution and susceptibility to infectious disease in the eastern oyster, Crassostrea virginica     

F. -L. E. Chu  R. C. Hale  A. Volety  G. Constantin 《Marine environmental research》1996,42(1-4)

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Preliminary attempt to characterize the rotation of seafloor in the Pito Deep area of the Easter Microplate using a submersible magnetometer     

R.N. Hey  F. Martinez  S. Diniega  D.F. Naar  J. Francheteau  R. Armijo  M. Constantin  J.P. Cogné  J. Girardeau  R. Hekinian  R. Searle 《Marine Geophysical Researches》2002,23(1):1-12

Several mechanisms have been proposed to account for the rotation of the nearly north-south abyssal hill fabric formed on the East Pacific Rise north of the Easter Microplate to the nearly east-west trends in the northern microplate interior. Proposed mechanisms include rigid microplate rotation, transform fault – parallel shear, and bookshelf faulting during the transfer of lithosphere from the Nazca Plate to the microplate. We used a submersible magnetometer on a NAUTILE dive program to measure the magnetic vector rotation of a pillow basalt and dike spur near Pito Deep, the present location of the tip of the propagating rift system that created the microplate. Our results, although too limited to draw strong conclusions from, suggest clockwise rotations of the seafloor magnetic vectors inconsistent with the transform-parallel shear model, and larger than can be explained solely by rigid microplate rotation.  相似文献   

Seismic response of self‐centring hysteretic SDOF systems     

Constantin Christopoulos  Andr Filiatrault  Bryan Folz 《地震工程与结构动力学》2002,31(5):1131-1150

The seismic response of single‐degree‐of‐freedom (SDOF) systems incorporating flag‐shaped hysteretic structural behaviour, with self‐centring capability, is investigated numerically. For a SDOF system with a given initial period and strength level, the flag‐shaped hysteretic behaviour is fully defined by a post‐yielding stiffness parameter and an energy‐dissipation parameter. A comprehensive parametric study was conducted to determine the influence of these parameters on SDOF structural response, in terms of displacement ductility, absolute acceleration and absorbed energy. This parametric study was conducted using an ensemble of 20 historical earthquake records corresponding to ordinary ground motions having a probability of exceedence of 10% in 50 years, in California. The responses of the flag‐shaped hysteretic SDOF systems are compared against the responses of similar bilinear elasto‐plastic hysteretic SDOF systems. In this study the elasto‐plastic hysteretic SDOF systems are assigned parameters representative of steel moment resisting frames (MRFs) with post‐Northridge welded beam‐to‐column connections. In turn, the flag‐shaped hysteretic SDOF systems are representative of steel MRFs with newly proposed post‐tensioned energy‐dissipating connections. Building structures with initial periods ranging from 0.1 to 2.0s and having various strength levels are considered. It is shown that a flag‐shaped hysteretic SDOF system of equal or lesser strength can always be found to match or better the response of an elasto‐plastic hysteretic SDOF system in terms of displacement ductility and without incurring any residual drift from the seismic event. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Effectiveness of simple approaches in mitigating residual deformations in buildings     

Didier Pettinga  Constantin Christopoulos  Stefano Pampanin  Nigel Priestley 《地震工程与结构动力学》2007,36(12):1763-1783

Developments in performance‐based seismic design and assessment approaches have emphasized the importance of considering residual deformations. Recent investigations have also led to a proposed direct displacement‐based design (DDBD) approach which includes an explicit consideration of the expected residual deformations as an integral part of the design process. Having estimated the expected residual deformations in a structure, engineers are faced with the problem of reducing them to meet the targeted performance levels under pre‐defined seismic hazard levels. Previous studies have identified the post‐yield stiffness as a primary factor influencing the magnitude of residual deformations in single degree of freedom and multiple degree of freedom structures. In this paper, a series of simple approaches to increase the post‐yield stiffness of traditional framed and braced systems for the purpose of reducing residual deformations are investigated. These methods do not utilize recentring post‐tensioned technology. This contribution addresses the feasibility of altering the lateral post‐yield stiffness of structural systems by: (i) using different reinforcement materials with beneficial features in their stress–strain behaviour; (ii) re‐designing the section geometry and properties of primary seismic‐resisting elements; and (iii) introducing a secondary elastic frame to act in parallel with the primary system. The efficiency of each of these techniques is investigated through monotonic and cyclic moment‐curvature and non‐linear time‐history analyses. Of these approaches the design and introduction of an elastic secondary system was found to be most effective and consistent in reducing residual deformations. A simplified design approach for achieving the desired increase of a system's post‐yield stiffness is also presented. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Petrology of the Easter microplate region in the South Pacific     

R. Hekinian  J. Francheteau  R. Armijo  J. P. Cogn  M. Constantin  J. Girardeau  R. Hey  D. F. Naar  R. Searle 《Journal of Volcanology and Geothermal Research》1996,72(3-4)

Submersible investigations along the East Rift segments, the Pito Deep and the Terevaka transform fault of the Easter microplate eastern boundary, and on a thrust-fault area of the Nazca Plate collected a variety of basalts and dolerites. The volcanics consist essentially of depleted (N-MORB), transitional (T-MORB) and enriched (E-MORB) basalts with low (0.01−0.1, < 0.7), intermediate (0.12–0.25, 0.7–1.2) and high (> 0.25, > 1.2–2) K/Ti and(La/Sm)_N ratios, respectively. The Fe-Ti-rich ferrobasalt encountered among the N-MORBs are found on the Pito Deep Central volcano, on the Terevaka intra-transform ridge, on the ancient (< 2.5 Ma) Easter microplate (called EMP, comprising the East Rift Inner pseudofaults and Pito Deep west walls) and on thrust-fault crusts. The most enriched (T- and E-MORB) volcanics occur along the East Rift at 25 °50′–27 °S (called 26 °S East Rift) and on the Pito seamount located near the tip of the East Rift at 23 °00′–23 °40′S (called 23 °S East Rift). The diversity in incompatible element ratios of the basalts in relation to their structural setting suggests that the volcanics are derived from a similar heterogenous mantle which underwent variable degrees of partial melting and magma mixing. In addition the Pito seamount volcanics have undergone less crystal fractionation (< 20%) than the lavas from the other Easter microplate structures (up to 35–45%). The tectonic segmentation of the East Rift observed between 23 and 27 °S corresponds to petrological discontinuities related to Mg# variations and mantle melting conditions. The highest Mg# (> 61) are found on topographic highs (2000–2300 m) and lower values (Mg# < 56) at the extremities of the East Rift segments (2500–5600 m depths). The deepest area (5600 m) along the East Rift is located at 23 °S and coincides with a Central volcano constructed on the floor of the Pito Deep. Three major compositional variabilities of the volcanics are observed along the East Rift segments studied: (1) the 26 °S East Rift segment where the volcanics have intermediate Na₈ (2.5–2.8%) and Fe₈ (8.5–11%) contents; (2) the 23 °S East Rift segment (comprising Pito seamount and Pito Deep Central volcano) which shows the highest (2.9–3.4%) values of Na₈ and a low (8–9%) Fe₈ content; and (3) the 25 °S (at 24 °50′–26 °10′S) and the 24 °S (at 24 °10′–25 °S) East Rift segments where most of the volcanics have low to intermediate Na₈ (2.6–2.0%) and a high range of Fe₈ (9–13%) contents. When modeling mantle melting conditions, we observed a relative increase in the extent of partial melting and decreasing melting pressure. These localized trends are in agreement with a 3-D type diapiric upwelling in the sense postulated by Niu and Batiza (1993). Diapiric mantle upwelling and melting localized underneath the 26, 25 and 23 °S (Pito seamount and Central volcano) East Rift segments are responsable for the differences observed in the volcanics. The extent of partial melting varies from 14 to 19% in the lithosphere between 18 and 40 km deep as inferred from the calculated initial (P_o=16kbar) and final melting (P_f=7kbar) pressures along the various East Rift segments. The lowest range of partial melting (14–16%) is confined to the volcanics from 23 °S East Rift segment including the Pito seamount and the Central volcano. The Thrust-fault area, and the Terevaka intra-transform show comparable mantle melting regimes to the 25 and 26 °S East Rift segments. The older lithosphere of the EMP interior is believed to have been the site of high partial melting (17–20%) confined to the deeper melting area (29–50 km). This increase in melting with increasing pressure is similar to the conditions encountered underneath the South East Pacific Rise (13–20 °S).  相似文献   

Development and validation of a metallic haunch seismic retrofit solution for existing under‐designed RC frame buildings     

Stefano Pampanin  Constantin Christopoulos  Te‐Hsiu Chen 《地震工程与结构动力学》2006,35(14):1739-1766

The feasibility and efficiency of a seismic retrofit solution for existing reinforced concrete frame systems, designed before the introduction of modern seismic‐oriented design codes in the mid 1970s, is conceptually presented and experimentally investigated. A diagonal metallic haunch system is introduced at the beam–column connections to protect the joint panel zone from extensive damage and brittle shear mechanisms, while inverting the hierarchy of strength within the beam–column subassemblies and forming a plastic hinge in the beam. A complete step‐by‐step design procedure is suggested for the proposed retrofit strategy to achieve the desired reversal of strength hierarchy. Analytical formulations of the internal force flow at the beam–column‐joint level are derived for the retrofitted joints. The study is particularly focused on exterior beam–column joints, since it is recognized that they are the most vulnerable, due to their lack of a reliable joint shear transfer mechanism. Results from an experimental program carried out to validate the concept and the design procedure are also presented. The program consisted of quasi‐static cyclic tests on four exterior, ? scaled, beam–column joint subassemblies, typical of pre‐1970 construction practice using plain round bars with end‐hooks, with limited joint transverse reinforcement and detailed without capacity design considerations. The first (control specimen) emulated the as‐built connection while the three others incorporated the proposed retrofitted configurations. The experimental results demonstrated the effectiveness of the proposed solution for upgrading non‐seismically designed RC frames and also confirmed the applicability of the proposed design procedure and of the analytical derivations. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Refractive index measurements of ammonia and hydrocarbon ices at 632.8 nm     

Constantin Romanescu  Ajeeta Khatiwada 《Icarus》2010,205(2):695-701

Optical constants in a broad temperature and wavelength range are important input parameters in radiative transfer models used in studies of planetary atmospheres. In the laboratory, the refractive index values of ices at the HeNe laser wavelength (632.8 nm) are often used to monitor the growth rate and thickness of ice films. In this report we present laboratory measurements determining the refractive index at 632.8 nm of ammonia and hydrocarbon ices in the temperature range 80-100 K. Thin ice films are vapor-deposited on a cryogenically cooled mirror located inside a high-vacuum apparatus. The real component of the refractive index of these ice films is determined by a two-angle interferometric technique. Optical modeling calculations of the transmittance and reflectance through the thin ice films assist in the interpretation of the experimental results. We discuss our results and compare them with other measurements available in the literature. The results reported here are relevant to the spectroscopy of icy objects in the solar system; they are needed to perform laboratory characterization of ices, derive optical constants, and model spectra.  相似文献   

Le développement du potentiel dans le cas d'une densité analytique     

Constantin Kholchevnikov 《Celestial Mechanics and Dynamical Astronomy》1971,3(2):232-240

The potential of a body of revolution is expanded in a series of spherical functions. It is proved that, for a body with analytical density limited by an analytical surface the coefficients of expansion decrease in geometrical progression.

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A hydrogeological conceptual approach to study urban groundwater flow in Bucharest city,Romania     

Mohamed Amine Boukhemacha  Constantin Radu Gogu  Irina Serpescu  Dragos Gaitanaru  Ioan Bica 《Hydrogeology Journal》2015,23(3):437-450

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