A unified model for bedform development and equilibrium under unidirectional,oscillatory and combined‐flows     

Mauricio M. Perillo  James L. Best  Miwa Yokokawa  Tomohiro Sekiguchi  Tomohiro Takagawa  Marcelo H. Garcia 《Sedimentology》2014,61(7):2063-2085

The development of bedforms under unidirectional, oscillatory and combined‐flows results from temporal changes in sediment transport, flow and morphological response. In such flows, the bedform characteristics (for example, height, wavelength and shape) change over time, from their initiation to equilibrium with the imposed conditions, even if the flow conditions remain unchanged. These variations in bedform morphology during development are reflected in the sedimentary structures preserved in the rock record. Hence, understanding the time and morphological development in which bedforms evolve to an equilibrium stage is critical for informed reconstruction of the ancient sedimentary record. This article presents results from a laboratory flume study on bedform development and equilibrium development time conducted under purely unidirectional, purely oscillatory and combined‐flow conditions, which aimed to test and extend an empirical model developed in past work solely for unidirectional ripples. The present results yield a unified model for bedform development and equilibrium under unidirectional, oscillatory and combined‐flows. The experimental results show that the processes of bedform genesis and growth are common to all types of flows, and can be characterized into four stages: (i) incipient bedforms; (ii) growing bedforms; (iii) stabilizing bedforms; and (iv) fully developed bedforms. Furthermore, the development path of bedform; growth exhibits the same general trend for different flow types (for example, unidirectional, oscillatory and combined‐flows), bedform size (for example, small versus large ripples), bedform shape (for example, symmetrical or rounded), bedform planform geometry (for example, two‐dimensional versus three‐dimensional), flow velocities and sediment grain sizes. The equilibrium time for a wide range of bed configurations was determined and found to be inversely proportional to the sediment transport flux occurring for that flow condition.  相似文献   

Effect of dust event timing on glacier runoff: sensitivity analysis for a Tibetan glacier     

Koji Fujita 《水文研究》2007,21(21):2892-2896

The impact of the timing of dust deposition on glacier runoff was evaluated using a glacier mass‐balance model with a newly improved scheme to track a dusted layer in a snow layer of a glacier. The lowering of surface albedo due to the dusted layer appearing leads to a drastic increase of glacier runoff even under the same meteorological conditions. Calculations of seasonal sensitivity, the relationship between dusted date and resulting runoff, have shown that dust deposition during a melting season might cause a drastic mass outflow from a glacier through changing the surface albedo during the melting season. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Effects of transport of pore water and material heterogeneity on strain localization of fluid‐saturated gradient‐dependent viscoplastic geomaterial     

Yosuke Higo  Fusao Oka  Mingjing Jiang  Yuji Fujita 《国际地质力学数值与分析法杂志》2005,29(5):495-523

The purpose of the present paper is to clarify the effects of permeability and initial heterogeneity on the strain localization of fluid‐saturated cohesive soil modelled by a strain gradient‐dependent poro‐viscoplastic constitutive model. The effects of permeability and gradient parameters on the growth rate of the fluctuation were obtained by a linear instability analysis. Deformation behaviour of clay specimens modelled as a viscoplastic model with a second order strain gradient during shear was numerically analysed by a soil–water coupled FEM under both globally undrained and partially drained conditions. It was found that the deformation pattern and the stress–strain curve greatly depend on the permeability, the drainage conditions and the initial non‐homogeneous properties. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Tectonic deformation buildup in folded mountain terrains in the October 23, 2004, Mid-Niigata earthquake     

Kazuo Konagai  Tomohiro Fujita  Takaaki Ikeda  Shigeki Takatsu 《Soil Dynamics and Earthquake Engineering》2009

The October 23, 2004, Mid-Niigata Earthquake jolted central Japan, causing serious damage in a mountainous region of Pliocene sedimentary rocks. Though aftershocks distribution showed a diffused pattern, it indicated that a blind-thrust fault having a NE–SW strike and inclined towards NW was the most causative. Tectonic deformation caused by this faulting was considered to be one of the causes of flooding that occurred about 8 months after the earthquake. Precise digital elevation models (DEMs) before and after the earthquake were obtained with stereoscopy for aerial photographs and laser imaging detection and ranging technology (LIDAR), respectively, and then compared to detect elevation changes and translations. Lastly, the changes of landforms due to landslides are excluded from the estimated deformations to obtain only the components of tectonic deformations of the ground surface.  相似文献   

Unstructured grid generation using LiDAR data for urban flood inundation modelling     

Ryota Tsubaki  Ichiro Fujita 《水文研究》2010,24(11):1404-1420

Inundation disasters, caused by sudden water level rise or rapid flow, occur frequently in various parts of the world. Such catastrophes strike not only in thinly populated flood plains or farmland but also in highly populated villages or urban areas. Inundation of the populated areas causes severe damage to the economy, injury, and loss of life; therefore, a proper management scheme for the disaster has to be developed. To predict and manage such adversity, an understanding of the dynamic processes of inundation flow is necessary because risk estimation is performed based on inundation flow information. In this study, we developed a comprehensive method to conduct detailed inundation flow simulations for a populated area with quite complex topographical features using LiDAR (Light Detection and Ranging) data. Detailed geospatial information including the location and shape of each building was extracted from the LiDAR data and used for the grid generation. The developed approach can distinguish buildings from vegetation and treat them differently in the flow model. With this method, a fine unstructured grid can be generated representing the complicated urban land features precisely without exhausting labour for data preparation. The accuracy of the generated grid with different grid spacing and grid type is discussed and the optimal range of grid spacing for direct representation of urban topography is investigated. The developed method is applied to the estimation of inundation flows, which occurred in the basin of the Shin‐minato River. A detailed inundation flow structure is represented by the flow model, and the flow characteristics with respect to topographic features are discussed. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Flow behavior and microstructures of hydrous olivine aggregates at upper mantle pressures and temperatures     

Tomohiro?OhuchiEmail author  Takaaki?Kawazoe  Yuji?Higo  Akio?Suzuki 《Contributions to Mineralogy and Petrology》2017,172(8):65

Deformation experiments on olivine aggregates were performed under hydrous conditions using a deformation-DIA apparatus combined with synchrotron in situ X-ray observations at pressures of 1.5–9.8 GPa, temperatures of 1223–1800 K, and strain rates ranging from 0.8 × 10^?5 to 7.5 × 10^?5 s^?1. The pressure and strain rate dependencies of the plasticity of hydrous olivine may be described by an activation volume of 17 ± 6 cm³ mol^?1 and a stress exponent of 3.2 ± 0.6 at temperatures of 1323–1423 K. A comparison between previous data sets and our results at a normalized temperature and a strain rate showed that the creep strength of hydrous olivine deformed at 1323–1423 K is much weaker than that for the dislocation creep of water-saturated olivine and is similar to that for diffusional creep and dislocation-accommodated grain boundary sliding, while dislocation microstructures showing the [001] slip or the [001](100) slip system were developed. At temperatures of 1633–1800 K, a much stronger pressure effect on creep strength was observed for olivine with an activation volume of 27 ± 7 cm³ mol^?1 assuming a stress exponent of 3.5, water fugacity exponent of 1.2, and activation energy of 520 kJ mol^?1 (i.e., power-law dislocation creep of hydrous olivine). Because of the weak pressure dependence of the rheology of hydrous olivine at lower temperatures, water weakening of olivine could be effective in the deeper and colder part of Earth’s upper mantle.  相似文献   

Evaluation of various satellite sensors for waterline extraction in a coral reef environment: Majuro Atoll, Marshall Islands   总被引：4，自引：0，他引：4  

Hiroya Yamano  Hiroto Shimazaki  Tsuneo Matsunaga  Albon Ishoda  Caleb McClennen  Hiromune Yokoki  Kazuhiko Fujita  Yoko Osawa  Hajime Kayanne 《Geomorphology》2006,82(3-4):398-411

The ability of five satellite sensor bands (IKONOS band 4, Terra ASTER bands 3 and 4, and Landsat ETM+ bands 4 and 5) was examined to extract the waterline at coral reef coasts (Majuro Atoll, Marshall Islands) using different wavelength regions (near infrared [NIR] and shortwave infrared [SWIR]) and different spatial resolutions (4, 15, and 30 m). After performing georeferencing and normalization of the images, density slicing was used to extract the waterline. Comparisons of extracted waterline positions with ground-level data for eight transects and global positioning system (GPS) tracks of the island shorelines showed that NIR bands were superior to SWIR bands because of the characteristics of the coral reef coasts, including a lack of foam and suspended sediments (which can affect the NIR wavelength region, if present) and the presence of remnant water on reef flats during low tide (which can affect the SWIR wavelength region). A linear relationship was found between the estimation errors of waterline positions and the spatial resolutions of the NIR sensors. Analysis on estimation errors and image costs showed that Terra ASTER band 3 was the most cost-effective sensor for extracting waterlines with reasonable accuracy. The results serve as general guidelines for using satellite-derived data to estimate intertidal topography and detect and monitor shorelines in coral reef environments.  相似文献   

Paleoenvironmental interpretations of Quaternary reef deposits based on comparisons of 10 selected modern and fossil larger foraminifera from the Ryukyu Islands, Japan     

Kazuhiko  Fujita  Hiroaki  Shimoji  Koichi  Nagai 《Island Arc》2006,15(4):420-436

Abstract A new method for reconstructing depositional environments of larger foraminifera‐bearing limestones is proposed. First, depth and spatial distributions of empty tests of 10 foraminiferal taxa in a 1–2 mm size fraction were examined using 32 surface sediment samples collected from depths shallower than 200 m, located to the west of Miyako Island, Ryukyu Islands, northwest Pacific. Distributional ranges of empty tests in the 1–2 mm size fraction appear to be more limited than those including other size fractions in previous reports, partly because larger empty tests of each taxon are less easily transported than smaller ones. Multivariate analyses (Q‐mode cluster analysis and non‐metric multidimensional scaling ordination) based on binary (presence/absence) data of the 10 taxa delineate four sample groups, each of which corresponds to different depositional environments: nearshore zone/bay inlet; back‐reef to fore‐reef; outer shelf to shelf slope; and shelf slope distant from coral reefs. Next, these modern data were applied to reconstruct the depositional environment of a rock section distributed in the Shiratorizaki area (Irabu Island, Ryukyu Islands), which consists of larger foraminiferal limestone of the Pleistocene Ryukyu Group. Multivariate analyses were performed on the fossil plus the modern foraminiferal data to explore the possible relationship of the fossil associations with variations in modern associations, demonstrating that the fossil foraminiferal associations resemble the modern outer shelf associations. The modern analog technique was also applied to estimate paleobathymetry using fossil foraminiferal data. The results indicate that the section studied was deposited in outer shelf environments at depths between 53.5 and 98.6 m. These paleoenvironmental interpretations are consistent with previous studies based on sedimentary facies and the computer‐based expert system. The modern dataset and methods used in our work would be particularly useful for paleoenvironmental reconstructions of Quaternary reef and shelf carbonates along active margins of the northwest Pacific.  相似文献   

Test on full‐scale three‐storey steel moment frame and assessment of ability of numerical simulation to trace cyclic inelastic behaviour     

Masayoshi Nakashima  Tomohiro Matsumiya  Keichiro Suita  Dawei Liu 《地震工程与结构动力学》2006,35(1):3-19

A test on a full‐scale model of a three‐storey steel moment frame was conducted, with the objectives of acquiring real information about the damage and serious strength deterioration of a steel moment frame under cyclic loading, studying the interaction between the structural frame and non‐structural elements, and examining the capacity of numerical analyses commonly used in seismic design to trace the real cyclic behaviour. The outline of the test structure and test program is presented, results on the overall behaviour are given, and correlation between the experimental results and the results of pre‐test and post‐test numerical analyses is discussed. Pushover analyses conducted prior to the test predicted the elastic stiffness and yield strength very reasonably. With proper adjustment of strain hardening after yielding and composite action, numerical analyses were able to accurately duplicate the cyclic behaviour of the test structure up to a drift angle of 1/25. The analyses could not trace the cyclic behaviour involving larger drifts in which serious strength deterioration occurred due to fracture of beams and anchor bolts and progress of column local buckling. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Cenomanian (Upper Cretaceous) carbon isotope stratigraphy of terrestrial organic matter for the Yezo Group, Hokkaido, Japan     

Go-ichiro  Uramoto  Tomotaka  Fujita  Akinori  Takahashi  Hiromichi  Hirano 《Island Arc》2007,16(3):465-478

Abstract Carbon isotope fluctuations of sedimentary organic matter along the two geological traverses in the Yezo Group, Hokkaido, northern Japan, elucidate a detailed chemostratigraphy for the Cenomanian Stage on the northwestern Pacific margin. Visual characterization of the kerogen from mudstone samples shows that the major constituents of sedimentary organic matter originated as terrestrial higher plants. The atomic hydrogen/carbon ratios of the kerogen suggest that the original δ¹³C values of terrestrial organic matter (TOM) have not been affected significantly by thermal diagenesis. The patterns in two δ¹³C_TOM curves are similar and independent of changes in lithology and total organic carbon contents, which suggests that TOM was mixed sufficiently before the deposition in the Yezo forearc basin for the δ¹³C composition having been homogenized. In addition, this implies that the Hokkaido δ¹³C_TOM profiles represent the averaged temporal δ¹³C variations of terrestrial higher‐plant vegetation in the hinterlands of northeast Asia during Cenomanian time. Three shorter‐term (ca. 0.1 my duration) positive‐and‐negative δ¹³C_TOM fluctuations of ∼1‰ are present in the Lower to Middle Cenomanian interval in the Yezo Group. On the basis of the age‐diagnostic taxa (ammonoids, inoceramids and planktic foraminifers), these discrete δ¹³C_TOM events are interpreted to be correlated with those in the δ¹³C curves of pelagic carbonates from European basins. The correlation of δ¹³C events between the European and Yezo Group sections suggests that the shorter‐term δ¹³C fluctuations in Cenomanian ocean‐atmosphere carbon reservoirs are useful for global chemostratigraphic correlation of marine strata. In particular, the correlation of δ¹³C fluctuations of the so‐called ‘Mid‐Cenomanian event’ (MCE) implies: (i) the δ¹³C variations of global carbon reservoir during the MCE are precisely recorded in the δ¹³C_TOM records; and (ii) the MCE δ¹³C_TOM event is an efficient chronostratigraphic index for the Lower/Middle Cenomanian boundary of the Mid‐Cretaceous sequences.  相似文献