Seepage flow problems by variational inequalities: Theory and approximation     

Noboru Kikuchi 《国际地质力学数值与分析法杂志》1977,1(3):283-297

The theory of variational inequalities enables us to formulate and solve free boundary problems in fixed domains, while most other methods assume the position of the unknown domain in solving the problem. Here the problem of seepage flow through a rectangular dam with a free boundary is formulated as a vertical inequality following the ideas of Baiocchi. In order to demonstrate the essential ideas of extending the domain of the solution of problems with free boundaries, the problem of the deflection, of a string on a rigid support is first examined. Next, variational inequalities are derived which are associated with several cases of seepage problems. An approximation theory, including a priori error estimates, is developed using finite element methods, and an associated numerical scheme is given. It is shown that for linear and quadratic finite element methods, the rates of convergence are 0(h) and 0(h^1.25-δ), 0 < δ < 0.25, respectively, if the permeability is constant.  相似文献   

Structure of the Fram Strait branch of the boundary current in the Eurasian Basin of the Arctic Ocean     

Andrey V. Pnyushkov  Igor V. Polyakov  Vladimir V. Ivanov  Takashi Kikuchi 《Polar Science》2013,7(2):53-71

Recent mooring-based observations at several locations along the continental slope of the Arctic Ocean's Eurasian Basin showed a transformation of the Boundary Current (BC) from a mostly barotropic flow in Fram Strait to a jet-like baroclinic current northeast of Svalbard, and the reemergence of the barotropic structure of the flow in the eastern Eurasian Basin. This transformation is accompanied by a weakening of the flow from ～24 cm/s in Fram Strait to ～5 cm/s at the Lomonosov Ridge. The maximum of the baroclinic component of the BC at an intermediate depth (～200–370 m) is associated with the Atlantic Water core. The depth range of the baroclinic current maximum is controlled by cross-slope density gradients above and below the baroclinic velocity maximum as follows from the geostrophic balance of forces. According to the model simulations, the BC splits into shallow and deep branches in the proximity of Svalbard due to a divergence of isobaths, confirming topographically-controlled BC behavior. The shallow branch is located at a shelf break with a typical bottom depth of ～200 m and current speed of up to ～24 cm/s. The discussed results, which provide insight on some basic aspects of the dynamics of the BC (the major oceanic heat source for the Arctic Ocean), may be of importance for understanding of the ocean's role in shaping the arctic climate system state.  相似文献   

A relic coral fauna threatened by global changes and human activities, Eastern Brazil     

Leão ZM  Kikuchi RK 《Marine pollution bulletin》2005,51(5-7):599-611

Coral species composition of drilled cores from emergent bank reefs, and coral cover of the surface of old and living reefs located along the coast of the state of Bahia, Eastern Brazil, revealed that there is a marked change in the occurrence of the major building coral species in different time intervals of the reef structure, as well as in the living surface of reefs located in two different geographical sites. Holocene core sections from two reef areas (12 degrees 40'S-38 degrees 00'W and 18 degrees 00'S-39 degrees 00'W) have as major reef builders, on its topmost core interval (3 to 4 ky old), the endemic coral Mussismilia braziliensis Verrill, 1868, which also dominate on the 2.5-3.5 ky old surfaces of truncated reef tops. At the base of the cores (the 2m lower interval, older than 4 ky BP), another endemic coral Mussismilia harttii Verrill, 1868 is the dominant reef component. The relative abundance of M. braziliensis on the living surfaces of shallow reefs from both areas, shows that in the southern area, it is up to 98% on reefs located 60 km off the coast, in depths between 3 and 4m, but do not exceed 1.3% on the surface of the northern reefs located 1-2 km off the coast in depths 4-5m. The Holocene falling sea level that occurred along the coast of Brazil since 5.1 ky BP, causes an increasing runoff into the area of coastal reefs. This phenomenon may have affected the nearshore reef building fauna, replacing a more susceptive coral fauna with one better adapted to low light levels and higher sediment influx. The high turbidity associated with early Holocene shelf flooding, should also be responsible for the absence of M. braziliensis during the initial stages of reef buildup in Brazil. At the present time, the rapidly increasing human pressure, due to changes in land uses of the coastal zone (increasing sedimentation rate, nutrification of coastal waters, industrial pollution) and underwater practices, such as overfishing and an intense tourism, is aggravating the recovery capacity of this already naturally threatened coral community. If this situation coupled with increasing sea surface temperature persists, modern coral reef growth, in Brazil cannot be maintained and the major reef building coral species of the reefs in Bahia, a remnant endemic coral fauna will very soon appear in the list of endangered species.  相似文献   

Database of Comet Polarimetry: Analysis and Some Results     

Nikolai Kiselev  Vera Rosenbush  Klaus Jockers  Sergey Velichko  Sen Kikuchi 《Earth, Moon, and Planets》2005,97(3-4):365-378

We present the electronic database (EAR-C-COMPIL-5-DB-COMET-POLARIMETRY-V1.0, NASA Planetary Data System) involving published and some unpublished results of cometary polarimetry. The database contains more than 2600 measurements of linear and circular polarization for 64 comets since 1940s. The narrow-band and wide-band measurements within the spectral region 0.3–2.2 micron are presented. The ranges of phase angles, helio- and geocentric distances of comets are 0.4–122°, 0.6–4.8 AU, 0.03–4.9 AU, respectively. We have comprised more than 60 references to the published papers and unpublished sources. The data we included are presented in a tabular format in the ASCII codes. The database can be used as the observational basis for detailed theoretical modeling, interpretation of the phase-angle and spectral dependence of polarization, classification of comets, laboratory simulating, and for selecting future space-mission targets. Analysis of the available data allowed us to summarize some observed characteristics of linearly and circularly polarized light and their phase-angle, heliocentric, spectral, and spatial dependencies.  相似文献   

Structural evolutions of an obsidian and its fused glass by shock-wave compression     

K.?ShimodaEmail author  M.?Okuno  Y.?Syono  M.?Kikuchi  K.?Fukuoka  M.?Koyano  S.?Katayama 《Physics and Chemistry of Minerals》2004,31(8):532-542

Shock-recovery experiments for obsidian and its fused glass have been carried out with pressure up to 35 GPa. Structural evolution accompanying the shock compression was investigated using X-ray diffraction technique, Raman and infrared spectroscopy. The densities of obsidian and its fused glass increased with applied shock pressure up to 25 GPa. Densification reached a maximum of 4.7 and 3.6% for obsidian and its fused glass, respectively. The densification mechanism is attributed to reduction of the T–O–T angle, and changes in ring statistics in the structure. Density reduction observed at greater than 25 GPa of applied shock pressure is due to partial annealing of the high-density glass structures brought by high post-shock residual temperature. The density of fused glass is almost equal to its original value at 35 GPa while the shocked obsidian has a slightly lower value than its original value. Amorphization of crystallites present in the obsidian due to shock compression is probably the cause of the density decrease. The structural evolution observed in shock-compressed obsidian and its fused glass can be explained by densification resulting from average T–O–T angle reduction and increase of small rings, and subsequent structural relaxation by high post-shock temperature at applied shock compression above 25 GPa.  相似文献   

An X-ray diffraction study of shock-wave-densified SiO<Subscript>2</Subscript> glasses     

Y. Shimada  M. Okuno  Y. Syono  M. Kikuchi  K. Fukuoka  N. Ishizawa 《Physics and Chemistry of Minerals》2002,29(4):233-239

 The densification and structural changes in SiO₂ glass compressed up to 43.4 GPa by shock experiments are investigated quantitatively by the X-ray diffraction technique. Direct structural data (average Si–O and Si–Si distances and Si–O–Si angles, coordination number of the Si atom) of these shock-densified SiO₂ glasses have been obtained by analyzing the radial distribution function curves, RDF(r), calculated with X-ray diffraction data. The coordination number of all densified glasses is about 4 and shows almost no pressure variation. The SiO₂ glass has shown density increase of 11% at a shock compression of 26.3 GPa. This density evolution could not be explained by the coordination change. The reduction of the average Si–O–Si angle (144° at 0 GPa to 136° at 26.3 GPa) obtained from RDF(r) data may account for this density increase. This Si–O–Si angle change may be caused by shrinkage of the network structure and the increase of small rings of SiO₄ tetrahedra. For higher shock pressure, a decrease in the Si–O–Si angle to 140° was observed. This is consistent with the decrease in density at 32.0 and 43.2 GPa. This decrease in the Si–O–Si angle and density could be attributed to an annealing effect due to high after-shock residual temperature. This pressure dependence of average Si–O–Si angles in shock-densified SiO₂ glass agrees with the results of our previous Raman spectroscopic study. On the other hand, the pressure variation for the first sharp diffraction peak (FSDP) was analyzed to estimate the evolution of intermediate range structures. It is suggested that the mean d value (d _m ) obtained from the position of FSDP strongly depends on the shock and residual temperature, as well as shock pressure. Received: 29 June 2001 / Accepted: 14 November 2001  相似文献   

Crustal analysis of the Ulleung Basin in the East Sea (Japan Sea) from enhanced gravity mapping     

Chan Hong Park  Jeong Woo Kim  Nobuhiro Isezaki  Daniel R. Roman  Ralph R. B. von Frese 《Marine Geophysical Researches》2006,27(4):253-266

To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.  相似文献   

Geomagnetic anomaly pattern of the Japan Sea     

Nobuhiro Isezaki  Seiya Uyeda 《Marine Geophysical Researches》1973,2(1):51-59

Using all available geomagnetic data, including those obtained in a detailed survey conducted by the authors in 1970, the geomagnetic anomaly pattern if the Japan Sea has been studied. It has been established that sublinear magnetic anomalies run subparallel to the general trend of the Japanese Islands. The peak to peak amplitudes of most of these anomalies are less than 300y, their wavelengths 20 to 40 km. The anomalies are much less distinct in linearity than those found in the northwestern corner of the Pacific basin off northeastern Honshu. The linear trend is better developed in the deeper basin areas and less recognizable in the Yamato- and Kitayamato-areas. The anomaly pattern appears to support the view that the Japan Sea floor evolved through a spreading process from numerous spreading centers. A definite conclusion about the genesis of the Japan Sea, however, must await further investigation.  相似文献   

Grain size,La/Yb and Th/Sc of settling particles in the western North Pacific: Evidence for lateral transport of small Asian loess     

Nobuhiro Maeda  Shinichiro Noriki  Hisashi Narita 《Journal of Oceanography》2007,63(5):803-812

To understand the transport process of lithogenic particles in the ocean, we measured the grain size distributions of lithogenic particles and measured the opal, La, Yb, Th, and Sc concentrations of the settling particles collected from time-series sediment traps at Sta. KNOT (44°N, 155°E, water depth 5320 m) from June 2002 to May 2004. The annual mean lithogenic particle flux observed at the lower sediment trap (5100 m) was twice as high as that at the upper sediment trap (770 m). The contribution of Asian loess estimated by the La/Yb and the Th/Sc ratios in the lower layer was greater than that in the upper layer. The fluxes of small lithogenic particles with sizes of 3–4 μm at the lower layer (5 to 65 mg/m²/day) were approximately four times larger than that at the upper layer (0.6 to 27 mg/m²/day). These results indicate that the horizontal addition of small particle sizes of Asian loess is a main factor in the increase of lithogenic particles at the lower layer. The temporal variations in the small lithogenic particle flux at the lower layer had a positive correlation with those at the upper layer (r = 0.71). The small lithogenic particle fluxes showed a strong positive correlation with the opal fluxes (r = 0.9). We therefore conclude that the small lithogenic particles were laterally transported and scavenged by the formation of aggregates with opal.  相似文献   

A diametral deformation method forin situ stress and rock property measurement     

Shosei Serata  Shinji Kikuchi 《Geotechnical and Geological Engineering》1986,4(1):15-38

Summary Failure deformation of a borehole boundary in response to hydraulic loading via a plastic cylinder is directly related to both the initial stress state and the material properties of the ground. These relationships are utilized for determination ofin situ stress states and material properties of complex geological formations, including fractured hard rock and soft ductile media, by directly measuring diametral deformation of the borehole in relation to the applied pressure. This new method was first developed by means of finite element simulation models, and later confirmed by laboratory model studies. This method was then field tested in an outcropping of homogeneous sandstone and later applied to three underground geological formations: highly stratified shale, rock salt, and fractured green schist. Some of the results of these field applications are presented here to illustrate the validity and usefulness of this method, especially for complex ground where the conventional methods of overcoring and hydrofracturing may be ineffective. The instrumentation of this method involves a borehole probe which utilizes electrically powered hydraulic pumping and computerized data acquisition for rapid measurement and on-site analysis. The significance of the new method is its ability to obtain input data ofin situ stress states and material properties for finite element analysis of earth structures in complex ground.  相似文献