Seismic-response-controlled structure with active mass driver system. Part 1: Design     

Takuji Kobori  Norihide Koshika  Kazuhiko Yamada  Yoshiki Ikeda 《地震工程与结构动力学》1991,20(2):133-149

An Active Mass Driver (AMD) system is proposed to suppress actively the response of a building to irregular external excitations such as earthquakes and typhoons. This system has been introduced to an actual ten-storey office building for the first time in the world. The system controls the motions of a structure by means of an external energy supply. It consists of an auxiliary mass installed in a building and an actuator that operates the mass and produces a control force which counters disturbances to the building. The design method of the AMD system, including the location of the installation and the capacity and stability of the system, is proposed. Simplification of the control algorithm is also described.  相似文献   

Assimilation of simulated altimeter data in a two-layer linear Rossby wave model using the variational method     

Cong  L. Z.  Ikeda  M. 《Journal of Oceanography》1995,51(3):301-326

The variational assimilation method has been examined for ability of reconstructing mesoscale features in altimeter data using a simple dynamic model. A one-dimensional, two-layer Rossby wave model in a cross-track channel has been chosen. The simulated data are constructed from a theoretical solution, which is composed of any combination of two normal vertical (barotropic and baroclinic) modes. The data are collected along tracks and with repeat periods similar to those of the Geosat altimeter. The phase space of control variables is composed of initial and boundary conditions. A cost function is defined to measure differences between the simulated data and the model solution. Regularization (smoothing) terms are also included in the cost function in the form of secon-order spatial and time derivatives of the solution. In this paper, two potential problems existing in the altimeter data assimilation are addressed: one is low cross-track resolution, and the other is vertical projection of the data measured at the sea surface. A succesful metho is developed for reconstructing Rossby waves with wavelengths as short as twice the track intervals for any combination of two vertical modes. A key component to efficient assimilation is a preparation step prior to the actual variational assimilation: a uniform ratio of pressure amplitudes in the two layers is included as an optimization parameter. Starting with the first guess from the preparation step, the variational method is carried out based on adjoint equations without such constraint. Separation of the control variables into the two subsets of the initial and the boundary conditions is found useful. Characteristics of the Hessian matrix are related to the performance of this technique. The method developed for the linear system implies steps to be included in data assimilation for nonlinear meanders and eddies in a major current system as well.  相似文献   

Mesoscale variability along the east coast of India in spring as revealed from satellite data and OGCM simulations     

Prescilla Kurien  Motoyoshi Ikeda  Vinu K. Valsala 《Journal of Oceanography》2010,66(2):273-289

Since mesoscale features like meanders have great importance in nourishing the coastal fisheries, satellite data analyses and a numerical modeling study were carried out for the east coast of India during spring inter-monsoon time (March-May), when biological productivity is high. During this time, the East India Coastal Current (EICC) system appears as a northward flowing western boundary current of a seasonal subtropical gyre in the Bay of Bengal prior to the summer monsoon with a more intense upwelling in the coastal region. A relatively clear sky permits satellite remote sensing of Sea Surface Temperature (SST) and Chlorophyll-a (Chl-a), whose patterns were verified against geostrophic velocity in altimeter data: i.e., phytoplankton grows in colder and nutrient richer water bounded by the seaward meanders. Progression of meanders in the coastal current was revealed and compared with an eddy-resolving Ocean General Circulation Model (OGCM), which is capable of modeling wind-driven general circulation and each stage of the meander growth. The numerical solutions provided the following results, in reasonable agreement with the linear stability theory using a two-and-a-half layer quasi-geostrophic model. Baroclinic instability plays a key role for the meander growth and eddy generation, while meanders in the coastal current are initiated by isolated mesoscale rotations propagating westward. The baroclinically unstable meanders have a wavelength of 500∼700 km, grow in one month and propagate downstream of the coastal current at several kilometers per day. The instability is not strong enough for the meanders to detach an eddy from the western boundary current.  相似文献   

LiDAR-derived DEM evaluation of deep-seated landslides in a steep and rocky region of Japan   总被引：1，自引：0，他引：1  

Mio Kasai  Manabu Ikeda  Toshihiro Asahina  Kazunori Fujisawa 《Geomorphology》2009,113(1-2):57

In steep and rocky terrains, their rough surfaces make it difficult to create landslide inventories even with detailed maps/images produced from airborne LiDAR data. To provide objective clues in locating deep-seated landslides, the surface textures of a 5 km² steepland area in Japan was investigated using the eigenvalue ratio and slope filters calculated from a very high resolution LiDAR-derived DEM. The range of filter values was determined for each of a number of surface features mapped in the field and these included: cracked bedrock outcrops, coarse colluvial deposits, gently undulating surfaces, and smooth surfaces. Recently active slides commonly contained patches of ground in which deposition and erosion occurred together near the erosion front, or where cracked bedrock outcrops and coarse colluvial deposits coexisted under a gently undulating surface. The characteristic eigenvalue and slope filter values representing this sliding process were applied to maps of the DEM derived filter values to extract potential sites of recent landslide activity. In addition, the relationships between the filter values of deep-seated landslides at various stages of evolution within the field mapped area were extended to the entire study area, to assess the contribution that landslide evolution makes to change in the landscape as a whole. While landslide components made up the steepest as well as the gentlest parts of the landscape depending on their evolutionary stage, landslides were constantly coarsened and steepened by progressive erosion, probably initiated by river bank erosion at the foot of slopes.  相似文献   

Continental basalts in the accretionary complexes of the South-west Japan Arc: Constraints from geochemical and Sr and Nd isotopic data of metadiabase     

Hiroo Kagami  Masaki Yuhara  Shigeru Iizumi  Yoshiaki Tainosho  Masaaki Owada  Yasuo Ikeda  
  Osamu Okano  Shuji Ochi  Yoshikazu Hayama and  Terukazu Nureki 《Island Arc》2000,9(1):3-20

Abstract The Ryoke Belt is one of the important terranes in the South‐west Japan Arc (SJA). It consists mainly of late Cretaceous granitoid rocks, meta‐sedimentary rocks (Jurassic accretionary complexes) and mafic rocks (gabbros, metadiabases; late Permian–early Jurassic). Initial ?_Sr (+ 25– + 59) and ?_Nd (? 2.1–?5.9) values of the metadiabases cannot be explained by crustal contamination but reflect the values of the source material. These values coincide with those of island arc basalt (IAB), active continental margin basalt (ACMB) and continental flood basalt (CFB). Spiderdiagrams and trace element chemistries of the metadiabases have CFB‐signature, rather than those of either IAB or ACMB. The Sr–Nd isotope data, trace element and rare earth element chemistries of the metadiabases indicate that they result from partial melting of continental‐type lithospheric mantle. Mafic granulite xenoliths in middle Miocene volcanic rocks distributed throughout the Ryoke Belt were probably derived from relatively deep crust. Their geochemical and Sr–Nd isotopic characteristics are similar to the metadiabases. This suggests that rocks, equivalent geochemically to the metadiabases, must be widely distributed at relatively deep crustal levels beneath a part of the Ryoke Belt. The geochemical and isotopic features of the metadiabases and mafic granulites from the Ryoke Belt are quite different from those of mafic rocks from other terranes in the SJA. These results imply that the Ryoke mafic rocks (metadiabase, mafic granulite) were not transported from other terranes by crustal movement but formed in situ. Sr–Nd isotopic features of late Cretaceous granitoid rocks occurring in the western part of the Japanese Islands are coincident with those of the Ryoke mafic rocks. Such an isotopic relation between these two rocks suggests that a continental‐type lithosphere is widely represented beneath the western part of the Japanese Islands.  相似文献   

Geometry of the Nojima Fault at Nojima-Hirabayashi, Japan – I. A Simple Damage Structure Inferred from Borehole Core Permeability     

David A. Lockner  Hidemi Tanaka  Hisao Ito  Ryuji Ikeda  Kentaro Omura  Hisanobu Naka 《Pure and Applied Geophysics》2009,166(10-11):1649-1667

The 1995 Kobe (Hyogo-ken Nanbu) earthquake, M = 7.2, ruptured the Nojima fault in southwest Japan. We have studied core samples taken from two scientific drillholes that crossed the fault zone SW of the epicentral region on Awaji Island. The shallower hole, drilled by the Geological Survey of Japan (GSJ), was started 75 m to the SE of the surface trace of the Nojima fault and crossed the fault at a depth of 624 m. A deeper hole, drilled by the National Research Institute for Earth Science and Disaster Prevention (NIED) was started 302 m to the SE of the fault and crossed fault strands below a depth of 1140 m. We have measured strength and matrix permeability of core samples taken from these two drillholes. We find a strong correlation between permeability and proximity to the fault zone shear axes. The half-width of the high permeability zone (approximately 15 to 25 m) is in good agreement with the fault zone width inferred from trapped seismic wave analysis and other evidence. The fault zone core or shear axis contains clays with permeabilities of approximately 0.1 to 1 microdarcy at 50 MPa effective confining pressure (10 to 30 microdarcy at in situ pressures). Within a few meters of the fault zone core, the rock is highly fractured but has sustained little net shear. Matrix permeability of this zone is approximately 30 to 60 microdarcy at 50 MPa effective confining pressure (300 to 1000 microdarcy at in situ pressures). Outside this damage zone, matrix permeability drops below 0.01 microdarcy. The clay-rich core material has the lowest strength with a coefficient of friction of approximately 0.55. Shear strength increases with distance from the shear axis. These permeability and strength observations reveal a simple fault zone structure with a relatively weak fine-grained core surrounded by a damage zone of fractured rock. In this case, the damage zone will act as a high-permeability conduit for vertical and horizontal flow in the plane of the fault. The fine-grained core region, however, will impede fluid flow across the fault.  相似文献   

Thermal modeling for a parent body of Itokawa     

S. Wakita  T. Nakamura  T. Ikeda  H. Yurimoto 《Meteoritics & planetary science》2014,49(2):228-236

We modeled the possible parent bodies of Itokawa, which was heated within by the decay energy of ²⁶Al. Based on mineralogic studies of dust particles derived from Itokawa by the Hayabusa spacecraft, it appeared that they were thermally metamorphosed at a peak temperature of 800 °C, and kept at 700 °C or higher at 7.6 Myr after CAI formation. Our numerical results show that the parent bodies of Itokawa would have been larger than 20 km in radius and accreted at a period between 1.9 and 2.2 Myr after CAI formation, to satisfy mineralogic and isotopic evidence from dust particles.  相似文献   

Deformation path of amygdules in basic schists in Itoshima area,northern Kyushu,Japan          下载免费PDF全文

Takeshi Ikeda 《Island Arc》2018,27(4)

A deformation path of amygdules in basic schists that underwent contact metamorphism in Itoshima area, northern Kyushu, Japan, has been revealed using shape and internal microstructure of the amygdules. The amygdules are filled mainly with plagioclase that was recrystallized during the contact metamorphism. Crystal size of the plagioclase decreases with increasing aspect ratio of the amygdules. Some amygdules with low‐aspect ratio contain plagioclase showing flat twin boundaries. This suggests that such amygdules were undeformed after peak of the contact metamorphism and preserved the strain accumulated until then, which probably includes prograde stage of the contact metamorphism and former regional Renge metamorphism. In contrast, the amygdules with high‐aspect ratio underwent superimposition of deformation taking place after peak of the contact metamorphism. The strain analysis shows the constriction types for the former amygdules while the plane‐strain types for the latter. This reveals a deformation path of the amygdules such that the constrictional strain before the peak of contact metamorphism was partially overprinted by later flattening strain, showing the apparent plane‐strain types.  相似文献   

Hydraulic model tests for propagation of flow and sediment in floods due to breaking of a natural landslide dam during a mountainous torrent     

Takahiro Itoh  Akihiko Ikeda  Takahiko Nagayama  Takahisa Mizuyama 《国际泥沙研究》2018,33(2):107-116

During mountain torrents, large-magnitude floods may result from heavy rainfall and cause the breakage of landslide dams naturally formed by heavy rainfall, earthquakes, and so on. The characteristics of longitudinal spreading of clear water discharge and changes in flow depth must be clarified because the changes in peak depth have not yet been examined in steep-slope torrents and because there are few data on spreading of flash floods and related sedimentation in mountainous torrents. In the present study, experimental data were collected through hydraulic model tests over a rigid bed, and the spreading of water, fine sediment, bed load, and large boulders due to flooding are discussed assuming that flash flooding/debris flows occur in the upstream reach. The effects of changes in flow width, such as expansions and contractions in the flow width, as well as changes in meandering channels, sediment transportation, and spreading flow depth resulting from bores are examined using flume data for a steep-slope torrent. The data obtained in the present study reveal that fine sediment components are transported to the downstream reach if large-magnitude floods occur and that the spreading rate and peak lags of the fine sediment and water level indicate the occurrence of a flood in the upstream reach.  相似文献