Pre-Japan-ARGO: Experimental Observation of Upper and Middle Layers South of the Kuroshio Extension Region Using Profiling Floats     

Naoto Iwasaka  Toshio Suga  Kensuke Takeuchi  Keisuke Mizuno  Yasushi Takatsuki  Kentaro Ando  Taiyo Kobayashi  Eitarou Oka  Yasuko Ichikawa  Motoki Miyazaki  Hiroshi Matsuura  Kenji Izawa  Chan-Su Yang  Nobuyuki Shikama  Momoko Aoshima 《Journal of Oceanography》2003,59(1):119-127

We deployed two profiling floats in the region south of the Kuroshio Extension in March 2000. Temperature and salinity profiles from a depth of 1500 × 10⁴ Pa to the surface are reported every two and four weeks, respectively. The floats performed very well for first four months after deployment. Later they failed in surfacing for a few months when the sea surface temperature in the region was high. The salinity sensors seemed to suffer from some damage during their failure-in-surfacing period. Despite this trouble, the results clearly demonstrate that the profiling float is a very useful and cost-effective tool for physical oceanographic observation in the open sea. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A large-scale excavation in soft Holocene deposit and its elasto-viscoplastic analysis     

Fusao Oka  Naoki Takada  Kazuyuki Shimono  Yosuke Higo  Sayuri Kimoto 《Acta Geotechnica》2016,11(3):625-642

In the present study, the large-scale excavation in the construction is numerically back-analyzed using a soil–water-coupled finite element method with an elasto-viscoplastic model which considers the strain-induced degradation. The measurements of the deformation have been performed during the construction of a new railway station in Osaka, Japan, in which a large and deep excavation has been successfully carried out using a special deep mixing type of soil improvement method with earth retaining walls through the thick Holocene Osaka Umeda clay deposit. A comparison between the numerical results and the measurements of the excavation at Osaka shows that the simulation method can reproduce the overall deformation of the soft ground and the earth retaining walls including the time-dependent behaviour during the excavation and a deep mixing soil improvement method as an additional technique for stability are effective.  相似文献   

Numerical analysis of a one‐dimensional infiltration problem in unsaturated soil by a seepage–deformation coupled method     

F. Oka  S. Kimoto 《国际地质力学数值与分析法杂志》2011,35(5):544-568

A multiphase coupled elasto‐viscoplastic finite element analysis formulation, based on the theory of porous media, is used to describe the rainfall infiltration process into a one‐dimensional soil column. Using this framework, we have numerically analyzed the generation of pore water pressure and deformations when rainfall is applied to the soil. A parametric study, including rainfall intensity, soil–water characteristic curves, and permeability, is carried out to observe their influence on the changes in pore water pressure and volumetric strain. From the numerical results, it is shown that the generation of pore water pressure and volumetric strain is mainly controlled by material parameters α and n′ that describe the soil–water characteristic curve. A comparison with the laboratory results shows that the proposed method can describe very well the characteristics observed during the experiments of one‐dimensional water infiltration into a layered unsaturated soil column. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The Influence of Urban Street Characteristics on Pedestrian Heat Comfort Levels in Philadelphia     

Masayoshi Oka 《Transactions in GIS》2011,15(1):109-123

This article demonstrates a way to model the urban microclimate using a combination of statistical analysis and a geographic information system (GIS). Field measurements of ambient temperature and relative humidity were collected in various urban settings at ground level over two surface materials and at two different times of the day. A panel autoregressive (PAR) model was created to conduct a regression analysis capable of accounting for the spatial autocorrelation. With the PAR analyses, selected urban street characteristics showed varying effects over the different surface materials and at different times of the day. The overall influences were consistent with previous findings. PAR models were then applied in GIS to create thermal prediction maps for the study area to determine the hot and cool spots. Since GIS is the most commonly used technology among a wide range of researchers and professionals, this article provides a means to improve the synthesis, integration, and sharing of information to understand the relationship between the heat‐vulnerable population and heat stress within the urban environment. This methodology will be useful in the effort to reduce the heat‐related morbidity and mortality, which are expected to increase with projected global warming.  相似文献   

A computational model for dynamic strain localization in unsaturated elasto-viscoplastic soils     

Fusao Oka  Babak Shahbodagh  Sayuri Kimoto 《国际地质力学数值与分析法杂志》2019,43(1):138-165

  相似文献   

Two-dimensional consolidation analysis using an elasto-viscoplastic constitutive equation     

F. Oka  T. Adachi  Y. Okano 《国际地质力学数值与分析法杂志》1986,10(1):1-16

A two-dimensional consolidation analysis of clay deposits was made with an elasto-viscoplastic constitutive model and Biot's consolidation theory. One- and two-dimensional consolidation problems were analysed numerically by the finite element and finite difference methods. Results show that the proposed method can describe the effect of sample thickness and aging on consolidation phenomena. The two-dimensional behaviour of a clay foundation during the construction of embankments also was simulated.  相似文献   

A cyclic elastoplastic constitutive model and effect of non-associativity on the response of liquefiable sandy soils     

Fusao Oka  Sayuri Kimoto 《Acta Geotechnica》2018,13(6):1283-1297

A large number of constitutive models for geomaterials, such as soils and rocks, have been proposed over the last three decades. Those models have been implemented into computer codes and have been successfully used to solve practical engineering problems particularly under monotonic loading conditions. Compared with the models for monotonic loadings, more improvements for cyclic models are necessary in order to obtain more accurate predictions for the dynamic behavior of geomaterials, e.g., the behavior during earthquakes. A cyclic elastoplastic model has been developed in this study for sandy soils; it is based on the kinematical hardening rule with a yield function that includes the changes in the stress ratio and the mean effective stress considering the degradation of the yield surface. From a simulation with the present model, it has been found that strong non-associativity leads to a large decrease in the mean effective stress during cyclic deformations under undrained conditions, while the model with the associated flow rule does not. This result is quite important because the mean effective stress becomes almost zero at the state of full liquefaction. Compared with the experimental results, the model can accurately reproduce the cyclic behavior of soil.  相似文献   

Large deformation and failure analysis of river embankments subjected to seismic loading     

Shahbodagh  B.  Sadeghi  H.  Kimoto  S.  Oka  F. 《Acta Geotechnica》2020,15(6):1381-1408

Acta Geotechnica - A numerical model based on the theory of mixtures is proposed for the nonlinear large deformation and failure analysis of river embankments subjected to large earthquakes. The...  相似文献   

Role of the ocean in controlling atmospheric CO2 concentration in the course of global glaciations     

Akira Oka  Eiichi Tajika  Ayako Abe-Ouchi  Keiko Kubota 《Climate Dynamics》2011,37(9-10):1755-1770

Responses of ocean circulation and ocean carbon cycle in the course of a global glaciation from the present Earth conditions are investigated by using a coupled climate-biogeochemical model. We investigate steady states of the climate system under colder conditions induced by a reduction of solar constant from the present condition. A globally ice-covered solution is obtained under the solar constant of 92.2% of the present value. We found that because almost all of sea water reaches the frozen point, the ocean stratification is maintained not by temperature but by salinity just before the global glaciation (at the solar constant of 92.3%). It is demonstrated that the ocean circulation is driven not by the surface cooling but by the surface freshwater forcing associated with formation and melting of sea ice. As a result, the deep ocean is ventilated exclusively by deep water formation in southern high latitudes where sea ice production takes place much more massively than northern high latitudes. We also found that atmospheric CO₂ concentration decreases through the ocean carbon cycle. This reduction is explained primarily by an increase of solubility of CO₂ due to a decrease of sea surface temperature, whereas the export production weakens by 30% just before the global glaciation. In order to investigate the conditions for the atmospheric CO₂ reduction to cause global glaciations, we also conduct a series of simulations in which the total amount of carbon in the atmosphere?Cocean system is reduced from the present condition. Under the present solar constant, the results show that the global glaciation takes place when the total carbon decreases to be 70% of the present-day value. Just before the glaciation, weathering rate becomes very small (almost 10% of the present value) and the organic carbon burial declines due to weakened biological productivity. Therefore, outgoing carbon flux from the atmosphere?Cocean system significantly decreases. This suggests the atmosphere?Cocean system has strong negative feedback loops against decline of the total carbon content. The results obtained here imply that some processes outside the atmosphere?Cocean feedback loops may be required to cause global glaciations.  相似文献   

The default methods in the 2019 Refinement drastically reduce estimates of global carbon sinks of harvested wood products     

Kayo  Chihiro  Kalt  Gerald  Tsunetsugu  Yuko  Hashimoto  Seiji  Komata  Hirotaka  Noda  Ryu  Oka  Hiroyasu 《Carbon balance and management》2021,16(1):1-12

With a lack of United States federal policy to address climate change, cities, the private sector, and universities have shouldered much of the work to reduce carbon dioxide (CO2) and other greenhouse gas emissions. This study aims to determine how landcover characteristics influence the amount of carbon (C) sequestered and respired via biological processes, evaluating the role of land management on the overall C budget of an urban university. Boston University published a comprehensive Climate Action Plan in 2017 with the goal of achieving C neutrality by 2040. In this study, we digitized and discretized each of Boston University’s three urban campuses into landcover types, with C sequestration and respiration rates measured and scaled to provide a University-wide estimate of biogenic C fluxes within the broader context of total University emissions. Each of Boston University’s three highly urban campuses were net sources of biogenic C to the atmosphere. While trees were estimated to sequester 0.6 ± 0.2 kg C m−2 canopy cover year−1, mulch and lawn areas in 2018 emitted C at rates of 1.7 ± 0.4 kg C m−2 year−1 and 1.4 ± 0.4 kg C m−2 year−1, respectively. C uptake by tree canopy cover, which can spatially overlap lawn and mulched landcovers, was not large enough to offset biogenic emissions. The proportion of biogenic emissions to Scope 1 anthropogenic emissions on each campus varied from 0.5% to 2%, and depended primarily on the total anthropogenic emissions on each campus. Our study quantifies the role of urban landcover in local C budgets, offering insights on how landscaping management strategies—such as decreasing mulch application rates and expanding tree canopy extent—can assist universities in minimizing biogenic C emissions and even potentially creating a small biogenic C sink. Although biogenic C fluxes represent a small fraction of overall anthropogenic emissions on urban university campuses, these biogenic fluxes are under active management by the university and should be included in climate action plans.  相似文献