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31.
32.
Buoyancy-driven propagation of an isolated fluid-filled crack in rock: implication for fluid transport in metamorphism 总被引:1,自引:0,他引:1
Yoshito Nakashima 《Contributions to Mineralogy and Petrology》1993,114(3):289-295
A new model for upward transport of buoyant fluid released during metamorphism is proposed. The model is fluid transport by buoyancy-driven propagation of isolated fluid-filled cracks. The mechanical behavior of a two-dimensional, isolated, vertical, and fluid-filled crack in impermeable rock is investigated using linear fractire mechanics and fluid dynamics. The results show that steady-state crack propagation which causes long-distance transport of the fluid occurs when the vertical cross-sectional area of the crack exceeds a critical value. Propagation velocity and average thickness of the crack under the steady-state propagation regime are expressed explicitly by the following seven parameters: vertical crack length; rigidity, Poisson's ratio, and fracture toughness of the rock; fluid viscosity; density difference between the rock and the fluid; gravitational acceleration. An isolated H2O-filled crack of vertical length 100 m, for example, propagates upwards in the crust at 0.3 m/s with the average thickness 0.2 mm when the following likely values are assumed: 0.1 mPa s for the H2O viscosity; 3 MPa m1/2 for the fracture toughness of the crustal rock. The application of the obtained results to the transport of H2O released during metamorphism suggests that the number density of isolated cracks propagating in the crust is very low. Since the propagation velocity is high, our model is suitable particularly for fluid transport through hot quartz-rich rock where fluid-filled cracks have geologically short lifetimes. 相似文献
33.
Base shear capping buildings with graphite‐lubricated bases for collapse prevention in extreme earthquakes 下载免费PDF全文
Francesca Barbagallo Ikumi Hamashima Hongsong Hu Masahiro Kurata Masayoshi Nakashima 《地震工程与结构动力学》2017,46(6):1003-1021
Damage or collapse of buildings vulnerable to seismic forces may cause human casualties, and seismic upgrading of such structures is a practical solution to this deficiency. The study presented here proposes a simple approach to prevent structural collapse by separating the superstructure from its foundation to let the superstructure slide during extreme ground shaking. The sliding mechanism contributes to cap the horizontal force exerted on the superstructure. In such approach, the key is to maintain the friction force between the superstructure and the foundation sufficiently low and stable. This research proposes to realize a controlled sliding mechanism, which acts as a structural fuse, by means of carbon powder lubrication at the bases of the structure's columns. The fundamental behaviour of the proposed structural system, named the base shear capping building, is investigated by shaking table tests and numerical simulation. Both experimental and numerical results showed that graphite lubrication is an efficient and robust lubrication material, maintaining the friction coefficient between the steel column bases and mortar foundation at around 0.16. The sliding at the bases significantly reduced the acceleration transmitted to the superstructure, keeping the base shear coefficient not greater than about 0.40. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
34.
Taichiro Okazaki Masayoshi Nakashima Keiichiro Suita Tomohiro Matusmiya 《地震工程与结构动力学》2007,36(1):35-53
Interaction between the external wall cladding and the seismic load resisting frame was examined in a full‐scale cyclic loading test of a three‐storey steel building structure. The building specimen had Autoclaved Lightweight Concrete (ALC, also designated as Autoclaved Aerated Concrete) panels installed and anchored to the structural frame as external wall cladding, using a standard Japanese method developed following the 1995 Kobe earthquake. ALC panelling is among the most widely used material for claddings in Japan. In the test, the ALC panel cladding contributed little to the stiffness and strength of the overall structure, even under a very large storey drift of 0.04 rad. No visible damage was noted in the ALC panels other than minor cracks and spalling of the bottom of the panels in the first storey. Consequently, in a Japanese steel building with properly installed ALC panel cladding, the structural frame is likely to be little affected by its cladding, and the ALC panels are capable of accommodating the maximum storey drift generally considered in structural design without sustaining discernible damage. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
35.
Hide Yasuhara Naoki Kinoshita Hiroaki Ohfuji Dae Sung Lee Shinichiro Nakashima Kiyoshi Kishida 《Applied Geochemistry》2011,26(12):2074-2088
Examining the evolution of fracture permeability under stressed and temperature-elevated conditions, a series of flow-through experiments on a single rock fracture in granite has been conducted under confining pressures of 5 and 10 MPa, under differential water pressures ranging from 0.04 to 0.5 MPa, and at temperatures of 20–90 °C, for several hundred hours in each experiment. Measurements of fluid and dissolved mass fluxes, and post-experimental microscopy, were conducted to constrain the progress of mineral dissolution and/or precipitation and to examine its effect on transport properties. Generally, the fracture aperture monotonically decreased with time at room temperature, and reached a steady state in relatively short periods (i.e., <400 h). However, once the temperature was elevated to 90 °C, the aperture resumed decreasing and kept decreasing throughout the rest of the experimental periods. This reduction may result from the removal of the mineral mass from the bridging asperities within the fracture. Post-experimental observations by scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy (SEM-EDX), revealed the formation of several kinds of secondary minerals such as silica and calcite. However, the precipitated minerals seemed to have had little influence on the flow characteristics within the fracture, because the precipitation was limited to quite local and small areas. The evolving rates and ultimate magnitudes of the fracture aperture are likely to be controlled by the stress exerted over the contacting asperities and temperatures, and by the prescribed flow conditions. Thus, this complex behavior should be attributed to the coupled chemically- and mechanically-induced effect. A coupled chemo–mechano conceptual model, accounting for pressure and free-face dissolutions, is presented in this paper to follow the evolution of the fracture permeability observed in the flow-through experiments. This model addresses the two dissolution processes at the contacting asperities and the free walls within the fractures, and is also capable of describing multi-mineral dissolution behavior. The model shows that the evolution of a fracture aperture (or related permeability) and of element concentrations may be followed with time under arbitrary temperature and pressure conditions. The model predictions for the evolving fracture aperture and elements concentrations show a relatively good agreement with the experimental measurements, although it is not possible to replicate the abrupt reduction observed in the early periods of the experiments, which is likely to be due to an unaccounted mechanism of more stress-mediated fracture compaction driven by the fracturing of the propping asperities. 相似文献
36.
Hidetaka Nomaki Naohiko Ohkouchi Petra Heinz Hisami Suga Yoshito Chikaraishi Nanako O. Ogawa Kouhei Matsumoto Hiroshi Kitazato 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1488-1503
We conducted an in situ feeding experiment using 13C-labeled unicellular algae in Sagami Bay, Japan (water depth, 1450 m), in order to understand the fate of lipid compounds in phytodetritus at the deep-sea floor. We examined the incorporation of excess 13C into lipid compounds extracted from bulk sediments and benthic foraminiferal cells. 13C-enriched fatty acids derived from 13C-labeled algae were exponentially degraded during 6 days of incubation in the sediment. Subsequent enrichments in 13C in sedimentary n-C15, anteiso-C17, and C17 fatty acids indicated the microbial degradation of algal material and production of bacterial biomass in the sediment. We observed the incorporation of 13C-labeled algal phytol and fatty acids into foraminiferal cells. The compositions of 13C-labeled algal lipids in foraminiferal cells were different from those in the bulk sediments, indicating that foraminiferal feeding and digestion influenced the lipid distribution in the sediments. Furthermore, some sterols in Globobulimina affinis (e.g., 24-ethylcholesta-5,22-dien-3β-ol, 24-ethylcholest-5-en-3β-ol, and 23,24-dimethylcholesta-5,22E-dien-3β-ol) were newly produced via the modification of dietary algal sterols within 4–6 days. In addition to the effects of bacteria, feeding by benthic foraminifera can result in a significant reorganization of the composition of organic matter and influence benthic food webs and carbon cycling at the deep-sea floor. 相似文献
37.
Shoji Kojima María Constanza San Martín Toshiro Nagase Daisuke Nakashima Claudio Bisso Andrew Menzies 《Resource Geology》2021,71(1):80-90
Modes of occurrence of Au‐ and Ag‐bearing phases and their relation with associated hypogene ore minerals were examined with the objective to elucidate Au‐Ag distribution at the Esperanza porphyry deposit in the Eocene Centinela copper belt, using ore‐microscope modal analysis, semi‐quantitative analyses by automated mineralogy, electron probe microanalysis, and secondary ion mass spectrometer. The Esperanza hypogene mineralization is characterized by early‐stage chalcopyrite‐rich veinlets in the potassic alteration zone and later polymetallic stage with tennantite and galena in the chlorite‐sericitic alteration zone. Only the early‐stage chalcopyrite contains fine‐grained electrum (Au68Ag32 ‐ Au81Ag19) and hessite (Ag2Te), and thus yields positive correlations in Cu vs. Au and Cu vs. Ag grades that are clearly recognized in the hypogene sulfide zone. The early‐stage chalcopyrite grains frequently exhibit polysynthetic twinning suggestive of inversion from intermediate solid solution. These features suggest that the fine‐grained electrum and hessite are products exsolved in the cooling process with the intermediate solid solution to chalcopyrite inversion. In contrast, tennantite and galena of the later‐stage mineralization contain no detectable Ag, and it is thus proposed that the early‐stage inverted chalcopyrite is the principal storage of economically important precious metals. 相似文献
38.
Large-scale flow models constructed using standard coarsening procedures may not accurately resolve detailed near-well effects.
Such effects are often important to capture, however, as the interaction of the well with the formation can have a dominant
impact on process performance. In this work, a near-well upscaling procedure, which provides three-phase well-block properties,
is developed and tested. The overall approach represents an extension of a recently developed oil–gas upscaling procedure
and entails the use of local well computations (over a region referred to as the local well model (LWM)) along with a gradient-based
optimization procedure to minimize the mismatch between fine and coarse-scale well rates, for oil, gas, and water, over the
LWM. The gradients required for the minimization are computed efficiently through solution of adjoint equations. The LWM boundary
conditions are determined using an iterative local-global procedure. With this approach, pressures and saturations computed
during a global coarse-scale simulation are interpolated onto LWM boundaries and then used as boundary conditions for the
fine-scale LWM computations. In addition to extending the overall approach to the three-phase case, this work also introduces
new treatments that provide improved accuracy in cases with significant flux from the gas cap into the well block. The near-well
multiphase upscaling method is applied to heterogeneous reservoir models, with production from vertical and horizontal wells.
Simulation results illustrate that the method is able to accurately capture key near-well effects and to provide predictions
for component production rates that are in close agreement with reference fine-scale results. The level of accuracy of the
procedure is shown to be significantly higher than that of a standard approach which uses only upscaled single-phase flow
parameters. 相似文献
39.
The seismic capacity of beam‐to‐column connections in steel high‐rise frames is a matter of concern, particularly when they are subjected to long‐period ground motions. A previous full‐scale shaking table test conducted at the E‐Defense National Research Institute for Earth Science and Disaster Prevention in Japan disclosed cracks and fractures in such beam‐to‐column connections. This paper examines the effects of three types of beam‐to‐column connection retrofit: supplemental welds, wing plates, and a haunch. Quasi‐static member tests and a series of shaking table tests applied to a full‐scale specimen are conducted to quantify the respective performances of the retrofit schemes. The performance of a total of 28 connections tested by the member and shaking table tests is evaluated together with that of an additional 12 unretrofitted connections tested in the previous test. When the supplemental welds are applied only to the shear tab to the web, the connection fractures at the same instant as the connection without retrofit. The corresponding cumulative plastic rotation is not improved. When the supplement welds are further applied to the web‐to‐column connection, strain concentration at the bottom flange, primarily promoted by the presence of the RC floor slab, is significantly reduced, and the cumulative plastic rotation capacity is increased to eight times that of the connection without retrofit. For the wing plate connection and haunch connection, the critical section is moved from the beam end to the beam cross‐section corresponding to the tip of the wing plates or haunch, resulting in an improvement of ductility by eight times that of the unretrofitted connection. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
40.
LQR control with frequency‐dependent scheduled gain for a semi‐active floor isolation system 下载免费PDF全文
Yundong Shi Tracy C. Becker Sachi Furukawa Eiji Sato Masayoshi Nakashima 《地震工程与结构动力学》2014,43(9):1265-1284
Floor isolation is an alternative to base isolation for protecting a specific group of equipment installed on a single floor or room in a fixed‐base structure. The acceleration of the isolated floor should be mitigated to protect the equipment, and the displacement needs to be suppressed, especially under long‐period motions, to save more space for the floor to place equipment. To design floor isolation systems that reduce acceleration and displacement for both short‐period and long‐period motions, semi‐active control with a newly proposed method using the linear quadratic regulator (LQR) control with frequency‐dependent scheduled gain (LQRSG) is adopted. The LQRSG method is developed to account for the frequency characteristics of the input motion. It updates the control gain calculated by the LQR control based on the relationship between the control gain and dominant frequency of the input motion. The dominant frequency is detected in real time using a window method. To verify the effectiveness of the LQRSG method, a series of shake table tests is performed for a semi‐active floor isolation system with rolling pendulum isolators and a magnetic‐rheological damper. The test results show that the LQRSG method is significantly more effective than the LQR control over a range of short‐period and long‐period motions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献