Development of real-time pseudo dynamic testing     

Masayoshi Nakashima  Hiroto Kato  Eiji Takaoka 《地震工程与结构动力学》1992,21(1):79-92

This paper presents a study for the development of a system capable of performing real-time pseudo dynamic testing. The system combines the basics of the pseudo dynamic test with a dynamic actuator, a digital displacement transducer and a digital servo-mechanism. The digital servo-mechanism has been introduced to ensure accurate displacement and velocity control, in which digital feedback control with a time interval of 2 msec has been performed continuously during actuator motion. Using the system, pseudo dynamic tests under sinusoidal and earthquake ground motion are carried out for a structure having a viscous damper, demonstrating that a perfectly real-time pseudo dynamic test can be achieved by incorporating the modified central difference method into an extra buffer operation of the digital servo-mechanism. The responses solved by the pseudo dynamic tests are compared with the responses of the test structure as well as those obtained from post-numerical analysis, and it is found that the real-time pseudo dynamic test conducted in this study is accurate.  相似文献   

Two timescales in beach erosion due to decrease in sediment sources with special reference to the formation and reduction of the delta of the Kurobe River flowing into the Japan sea     

Yoshito Tsuchiya  Teruo Shibano  Hiroshi Suyama  Toshiaki Yoshimura 《Natural Hazards》1988,1(1):45-65

Beach erosion has advanced in many countries of the world, especially in Japan, because of a decrease in sediment sources from rivers and a lack of longshore sediment transport from the adjacent coasts due to coastal structures. The former cause concerns the reduction of river deltas due to a decrease in sediment input from the river. Two timescales important in beach erosion, a longer timescale which concerns a change in the location of the river mouth, and a shorter one which is due to a decrease in longshore sediment transport, are discussed in the formation and reduction of the delta of the Kurobe River. Based on these timescales, beach erosion control is considered.  相似文献   

Escapement from a Diamond IX midwater trawl during acoustic surveys for capelin (Mallotus villosus) in the Northwest Atlantic     

Nakashima  B. S. 《ICES Journal of Marine Science》1990,47(1):76-82

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Earthquakes produce carbon dioxide in crustal faults     

Vincent Famin  Satoru Nakashima  Anne-Marie Boullier  Koichiro Fujimoto  Tetsuro Hirono 《Earth and Planetary Science Letters》2008,265(3-4):487-497

Fourier transform infrared (FTIR) microanalysis of pseudotachylytes (i.e. friction-induced melts produced by seismic slip) from the Nojima fault (Japan) reveals that earthquakes almost instantaneously expel 99 wt.% of the wall rock CO₂ content. Carbon is exsolved because it is supersaturated in the friction melts. By extrapolation to a crustal-scale fault rupture, large events such as the M7.2 Kobe earthquake (1995) may yield a total production of 1.8 to 3.4 × 10³ tons CO₂ within a few seconds. This extraordinary release of CO₂ can cause a flash fluid pressure increase in the fault plane, and therefore enhance earthquake slip or trigger aftershocks; it may also explain the anomalous discharge of carbon monitored in nearby fault springs after large earthquakes. Because carbon saturation in silicate melts is pressure-dependent, FTIR can be used as a new tool to constrain the maximum depth of pseudotachylyte formation in exhumed faults.  相似文献   

Numerical characteristics of peer‐to‐peer (P2P) internet online hybrid test system and its application to seismic simulation of SRC structure     

Tao Wang  Nobuya Yoshitake  Peng Pan  Tae‐Hyung Lee  Masayoshi Nakashima 《地震工程与结构动力学》2008,37(2):265-282

The peer‐to‐peer (P2P) Internet online hybrid test system has been developed for the seismic simulation of a structure. In this study, the stability and accuracy of the system are investigated analytically by studying the spectral radius of the recursive matrix of the test scheme featuring a two‐round quasi‐Newton test scheme. The applicability of the system is further examined by exploring the seismic responses of a complex structure, a steel‐encased reinforced concrete (SRC) structure with a steel tower on the top. The structure is divided into two numerical substructures and one tested part for hybrid test. The numerical substructures are simulated by sophisticated finite element method (FEM) models with material nonlinearities to capture local plastifications. Two types of FEM programs, namely OpenSEES and ABAQUS, which are suitable for the SRC part and the steel tower, respectively, are employed. The results demonstrate that the P2P system is able to simulate complex structures with significant nonlinearities. As compared with the previous study in which two elastic numerical substructures were considered, increase in the number of iterations in this study is not significant, because the associated nonlinearities are limited due to the small time interval adopted in the test. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Color-change processes of a plinian pumice and experimental constraints of color-change kinetics in air of an obsidian   总被引：1，自引：0，他引：1  

Mihoko Moriizumi  Satoru Nakashima  Satoshi Okumura  Yuta Yamanoi 《Bulletin of Volcanology》2009,71(1):1-13

Colors of plinian pumices were measured by spectrocolorimetry, and their quantitative color parameters in the L*a*b* color space were determined. A series of heating experiments of obsidian was conducted to simulate the color-change processes of rhyolitic glasses. In these experiments, following three stages of color-change processes were observed. Stage I showed a rapid b* (yellowishness) increase associated with fast dehydration controlled by water diffusivity (D _water). In stage II, a* (reddishness) increase was accompanied by Fe²⁺ decrease. Both a* increase and Fe²⁺ decrease can be simulated by a diffusion model. Obtained diffusivity D _oxidation were about two orders of magnitude smaller than D _water . The a*-value increase after the oxidation in stage III appeared to be quasi-linear with time, indicating the zeroth order reaction corresponding to the formation of hematite-like structures in rhyolitic glasses. The diffusion-limited a* increase model in stage II was applied to a natural plinian pumice fall unit to evaluate time periods of color-change processes through oxidation by air of fragmented rhyolitic materials.  相似文献   

Laboratory measurements of guided‐wave propagation within a fluid‐saturated fracture          下载免费PDF全文

Shinichiro Nakashima  Valeri A. Korneev 《Geophysical Prospecting》2016,64(1):143-156

A fluid‐saturated flat channel between solids, such as a fracture, is known to support guided waves—sometimes called Krauklis waves. At low frequencies, Krauklis waves can have very low velocity and large attenuation and are very dispersive. Because they propagate primarily within the fluid channel formed by a fracture, Krauklis waves can potentially be used for geological fracture characterization in the field. Using an analogue fracture consisting of a pair of flat slender plates with a mediating fluid layer—a trilayer model—we conducted laboratory measurements of the velocity and attenuation of Krauklis waves. Unlike previous experiments using ultrasonic waves, these experiments used frequencies well below 1 kHz, resulting in extremely low velocity and large attenuation of the waves. The mechanical compliance of the fracture was varied by modifying the stiffness of the fluid seal of the physical fracture model, and proppant (fracture‐filling high‐permeability sand) was also introduced into the fracture to examine its impact on wave propagation. A theoretical frequency equation for the trilayer model was derived using the poroelastic linear‐slip interface model, and its solutions were compared to the experimental results.  相似文献   

Water diffusivity in rhyolitic glasses as determined by in situ IR spectroscopy     

S.?OkumuraEmail author  S.?Nakashima 《Physics and Chemistry of Minerals》2004,31(3):183-189

The dehydration rate of hydrous rhyolitic glasses at 475–875 °C was measured by in situ infrared (IR) spectroscopy in order to determine the diffusion coefficient of water in rhyolitic glasses. The IR spectra of glass thin sections were obtained at 90-s intervals during 90 min at high temperatures, and the change in absorbance at 3550 cm^–1 corresponding to total water was monitored. The diffusion coefficients obtained from dehydration rates of the rhyolitic glasses are considered to be averaged value over the water-concentration profile in the sample. The averaged apparent diffusion coefficients increase with the initial total water content from 0.20 m² s^–1 for 0.7 wt% to 0.37 m² s^–1 for 2.8 wt% at 700 °C. The apparent activation energy for the diffusion of total water decreases with increasing initial water content from 112 ± 6 kJ mol^–1 for 0.7 wt% to 60 ± 17 kJ mol^–1 for 4.1 wt%. Assuming a linear relation between the diffusion coefficient of total water and the total water content, the diffusion coefficients at each initial total water content were also determined. The diffusion coefficients of total water at the water contents of 0.7 and 1.9 wt% and at 0.1 MPa were best fitted by ln D=[(12.9 ± 0.8) – (111 500 ± 6400)/RT] and ln D=[(10.6 ± 0.4) – (86 800 ± 2800)/RT], respectively, and are in agreement with previous data (D in m² s^–1, T in K). The present in situ IR dehydration experiment is a rapid and effective method for the determination of water diffusivity at high temperatures.  相似文献   

Carbon and hydrogen isotope variation of plant biomarkers in a plant-soil system   总被引：2，自引：0，他引：2  

Yoshito Chikaraishi  Hiroshi Naraoka 《Chemical Geology》2006,231(3):190-202

Stable carbon (δ¹³C) and hydrogen (δD) isotopic compositions of n-alkanes, anteiso-alkanes, n-alkanoic acids, n-alkanols, phytol and sterols in raw leaves of Acer argutum and Acer carpinifolium, their fallen leaves, mold and soils from a natural Acer forest were measured in order to: (1) understand isotopic variation of the plant biomarkers in a plant-soil system and (2) evaluate which biomarker is the most effective recorder of soil vegetation. Long-chain (> C₂₄) n-alkanes, n-alkanoic acids and n-alkanols are gradually enriched in ¹³C up to 12.9‰ (average of 4.3‰) and depleted in D up to 94‰ (average of 55‰) from raw leaves to soils. However, anteiso-alkanes, phytol and sterols show little variation in both δ¹³C (< ± 1‰) and δD (< ± 2‰) from raw leaves to soils. These isotope signatures in a plant-soil system indicate that isoprenoid plant biomarkers such as sterols in soils faithfully preserve the isotopic compositions of dominant higher plants growing on the soils without a diagenetic effect upon the isotopic compositions. In contrast, long-chain n-alkyl molecules in soils undergo specific isotopic modification during biodegradation associated with early diagenesis and/or a significant contribution from heterotrophic reworking.  相似文献   

Estimation of the apertures of water-saturated fractures by nuclear magnetic resonance well logging   总被引：1，自引：0，他引：1  

Yoshito Nakashima  Tsuneo Kikuchi 《Geophysical Prospecting》2007,55(2):235-254

Fracture aperture is an important transport property in subsurface hydrology because it influences well productivity and the volume of the water resource. Nuclear magnetic resonance (NMR) well logging measures the hydrogen‐bearing fluid molecules in porous or fractured strata, and the NMR signal intensity increases with the amount of fluid in the sensed region of the NMR sonde. Fluid confined in a large fracture of >>0.2 mm in aperture has T2 (i.e. spin‐spin relaxation time) values as long as those of the bulk fluid. The bulk‐fluid porosity (i.e. porosity calculated using this long T2 component in a T2 histogram data) increases linearly with aperture. Therefore, NMR logging enables quantitative estimation of fracture apertures of >>0.2 mm using the bulk‐fluid porosity data if the calibration of the NMR sonde is performed adequately. We applied NMR logging to a borehole in a Holocene andesite lava at Sumikawa, Japan, to estimate the aperture of open fractures within the lava. A test well of 100 m depth and 20 cm diameter, filled with bentonite drilling mud, was scanned with an NMR sonde to obtain a profile of the porosity and the T2 histogram of the andesite. The bulk‐fluid porosity was calculated from the T2 histogram data, as the porosity at which the T2 value is larger than or equal to a threshold T2 of bulk bentonite mud. The bulk‐fluid porosity of a specific inclined fracture responsible for the total loss of circulation at 61.2 m depth during drilling was calculated assuming a threshold or T2 cut‐off of 33 ms, and again for a cut‐off of 100 ms. Calibration of the NMR sensor in a laboratory and measurement of the fracture dip angle by electrical microimaging logging enabled us to estimate the fracture aperture as 1.7 cm, assuming a T2 cut‐off of 33 ms, or 1.6 cm for a T2 cut‐off of 100 ms. The method of aperture determination described in this study is independent of fluid species and lithology, and is applicable to various hydrogen‐bearing borehole fluids (clean water, mud and oil) and geological settings.  相似文献