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111.
Tokuo Yamamoto 《Marine Georesources & Geotechnology》2013,31(2):93-130
Abstract The problem of forced vibration of a slightly inelastic porous bed by water waves is treated analytically on the basis of a linearized expression of the nonlinear damping term for the grain‐to‐grain friction in bed soils and the linear theory by Biot (1962a [Jour. Appl. Physics, 33:1482–1498]) on the elastic wave propagation in porous media. A dispersion relation of water waves is obtained as a function of wave frequency, water depth, permeability, Poisson's ratio, rigidity, and specific loss of bed soil. Three types of elastic waves are induced in a bed by water waves: a shear wave and a compressional wave in the skeletal frame of soil, and a compressional wave in the pore fluid. The compressional wave, due to the motion of the pore fluid relative to the skeletal frame of soil, is highly damped by the viscosity of pore fluid and only a short range effect near the boundaries of discontinuity, such as a sea‐seabed interface. The seabed response to water waves is characterized by the two Mach numbers, i.e., the ratio of water‐wave speed to shear‐wave speed in soil and the ratio of water‐wave speed to compressional‐wave speed in soil. Most of the water‐wave propagation problems fall into the subsonic flow condition, where elastic waves in the bed travel faster than water waves. For sandy beds, generally the speeds of compressional and shear waves are much higher than the phase velocity of the water wave. For this case, the solution of the Coulomb‐damped poroelastic bed response presented in this paper approaches the solution of the massless poroelastic bed response in Yamamoto et al. (1978 [Jour. Fluid Mech., 87(1): 193–206]). The damping of water waves due to internal grain‐to‐grain friction is equally or more significant than the damping due to percolation in sand beds. For clay beds, the speed of the shear wave in soil becomes low and comparable to the phase speed of the water wave. The bed motion for this case is considerably amplified due to the near‐resonance vibration of shear mode of bed vibration. The water wavelength on a clay bed is significantly shortened compared to the water wavelength over a rigid bed. The water wave damping due to internal grain‐to‐grain friction in soil becomes much larger compared to the water wave damping due to percolation in clay beds. Long water waves over a soft clayey bed attenuate within several wavelengths of travel distance. 相似文献
112.
Damping systems that are effective over a wide range of displacement amplitudes using metallic yielding component and viscoelastic damper in series 下载免费PDF全文
A damper system that absorbs energy over a wide range of displacement amplitudes during building vibration was proposed. This system uses a serial connection of a metallic yielding component and viscoelastic damper with a displacement limit mechanism. Three types of the system were developed and tested: a diagonal bracing type, inverted V bracing type, and wall type. The test results showed that all these systems have damping ratios higher than 8% at small vibration amplitudes on the order of 0.1 mm. For a large vibration, a displacement limit mechanism with two pins limited the displacement of the viscoelastic damper as designed. Analytical simulations established that the system reduced the acceleration and the story drift to 60–70% and 80%, respectively, during a small earthquake compared with a conventional metallic yielding damper system. Furthermore, it showed an equivalent control performance during a severe earthquake. The damper system requires that a clearance be maintained for the displacement limit mechanism. However, this may be lost through construction error, residual displacement after an earthquake, and temperature effects. The changes in the clearance due to these effects were discussed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
113.
Kyunghoi Kim Tadashi Hibino Tamiji Yamamoto Shinjiro Hayakawa Yugo Mito Kenji Nakamoto In-Cheol Lee 《Marine pollution bulletin》2014
Field experiments were carried out to evaluate the effect of Granulated Coal Ash (GCA) on remediation of coastal sediments in terms of removing phosphates and hydrogen sulfide. Phosphate concentrations in the sediment were kept below 0.2 mg/l after the application of GCA, whereas those in the control sites increased up to 1.0 mg/l. The concentration of hydrogen sulfide in the sediment was maintained at almost zero in the experimental sites (GCA application sites) for over one year, whereas it ranged 0.1–2.4 mg S L−1 in control sites. Meanwhile, individual number of benthos increased in the experimental sites by several orders of magnitude compared to the control sites. The major process involved in hydrogen sulfide removal by GCA was thought to be the increase in pH, which suppresses hydrogen sulfide formation. From our findings, we concluded that GCA is an effective material for remediating organically enriched coastal sediment. 相似文献
114.
We propose that competent layers composed of silicified rocks in the Cretaceous Ryoke low-pressure/temperature (low- P/T ) metamorphic belt in the Iwakuni–Yanai area, Southwest Japan, may be an exhumed equivalent of a seismically-reflective bright-layer in the middle crust. Silicified rocks crop out as layers or long lenticular bodies several to fifteen meters in thickness, and they are restricted to the area of greenschist facies conditions within a structural thickness of about one kilometer. The silicified rock layers exhibit a sharp contact with subjacent biotite schist but a gradational contact with overlying pelitic schist. Silicified rock is mainly composed of fine-grained quartz and minor muscovite and biotite, and some colored minerals have been variably decolorized by alteration. This implies that silicification turned the color of pelitic schists to pale gray or milky white. Quartz veins cutting schistosity at high angles were preferentially developed in the silicified rocks, while schistosity-parallel quartz veins, which underwent viscous flow, were observed in the underlying biotite schists. En echelon quartz veins and fishnet-like quartz veins are characteristic of silicified rocks. The modes of occurrence of quartz veins indicate that silicified rocks were competent relative to underlying biotite schist. The combination of contact with high-competence contrast adjacent to low-permeability silicified rocks may be a good reflector of seismic waves. If the silicified rocks were distributed in the middle crust to a considerable extent, they may result in seismic bright-layer reflections. 相似文献
115.
Hiroshi Yamamoto Natsumi Nakamori Masaru Terabayashi Hafiz Ur Rehman Masahiro Ishikawa Yoshiyuki Kaneko Takashi Matsui 《Island Arc》2010,19(3):458-469
Geological observations in the Horoman area, south‐central Hokkaido, show that the Horoman peridotite complex of the Hidaka metamorphic belt is a tectonic slice about 1200 m thick. The peridotite slab is intercalated into a gently east‐dipping structure. The underlying unit is a Cretaceous–Paleogene accretionary complex. Riedel shear planes in the sedimentary layers of the accretionary complex near the structural bottom of the peridotite slab indicate top‐to‐the‐west (thrust) displacement. The overlying unit is composed of felsic–pelitic gneisses and mafic–felsic intrusive rocks (the Hidaka metamorphic rocks). The boundary surface between the peridotite complex and metamorphic rocks forms a domal structure. Microstructures of sheared metamorphic rocks near the structural top of the peridotite slab indicate top‐to‐the‐east (normal) displacement. The results combined with previous studies suggest that the Horoman peridotite complex was emplaced onto the Asian margin (Northeast Japan) during the collision between the Asian margin and the Hidaka crustal block. 相似文献
116.
Ryoshi Ishiwatari Koichi Negishi Hiroyasu Yoshikawa Shuichi Yamamoto 《Organic Geochemistry》2009,40(4):520-530
Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/Norg values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m?2 yr?1 in the Holocene, while it is ~60 g C m?2 yr?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C27–C31 alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C29 sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake. 相似文献
117.
In a disk with a low optical depth, dust particles drift radially inward by the Poynting-Robertson (P-R) drag rather than are blown out by stellar radiation pressure following destructive collisions. We investigate the radial distribution of icy dust composed of pure ice and refractory materials in dust-debris disks taking into account the P-R drag and ice sublimation. We find that icy dust particles form a dust ring by their pile-ups at the edge of their sublimation zone, where they sublime substantially at the temperature 100-110 K. The distance of the dust ring is 20-35 AU from the central star with its luminosity L??30L⊙ and 65(L?/100L⊙)1/2 AU for L??30L⊙, where L⊙ is the solar luminosity. The effective optical depth is enhanced by a factor of 2 for L??100L⊙ and more than 10 for L??100L⊙. The optical depth of the outer icy dust disk exceeds that of the inner disk filled with refractory particles, namely, the residue of ice sublimation, which are further subjected to the P-R effect. As a result, an inner hole is formed inside the sublimation zone together with a dust ring along the outer edge of the hole. 相似文献
118.
119.
Tsuyoshi Komiya Akinobu Suga Tsuyoshi Ohno Jian Han Junfeng Guo Shinji Yamamoto Takafumi Hirata Yong Li 《Gondwana Research》2008,14(1-2):209
Deciphering the drastic changes of surface environment and the emergence of animals after the Neoproterozoic Snowball Earth event are important for understanding the changes of surface environment and its influence on the evolution of life through geologic time. Especially, the emergence of two types of Metazoan animals such as animal embryo fossils, cnidarians or sponges, and Ediacaran fauna in the late Neoproterozoic was one of the critical turning points in the biological evolution.Calcium is one of the essential elements for the growth of most animals. In this study, in order to evaluate the Ca cycles in the Neoproterozoic, we have measured Ca isotopic ratios (44Ca/42Ca and 43Ca/42Ca) for phosphorite, dolostone and phosphatic animal embryo fossils with a multiple collector, inductively coupled plasma-mass spectrometer (MC-ICP-MS). The resulting 44Ca/42Ca ratio defined by the relative deviation from the ratio of NIST SRM915a (δ44/42CaNIST915) for phosphorite and dolostone ranges from 0.83 to 0.95‰, demonstrating that the fractionation between phosphorite/dolostone and seawater was very small. This evidence indicates that at the emergence of the Weng'an biota seawater was deficient in Ca probably due to mass deposition of phosphorite/dolostone and to the beginning of Ca-biomineralization.Three phosphatic animal embryo fossils have lower δ44/42Ca values than the phosphorite and dolomite, implying that the precursor of the phosphatic embryo fossils was able to fractionate Ca isotopes through Ca-biomineralization, consistent with marine gastropods. 相似文献
120.
Takashi Yamamoto 《Planetary and Space Science》1979,27(3):273-284
Based on the model calculation of VLF hiss power flux spectrum resulting from convective beam amplification of incoherent Cerenkov whistler radiation by the beam of precipitating auroral electrons, which has been developed by Maggs (1976), we examine the altitude dependence of power flux levels. Their strong altitude dependence leads us to suggest that non-linear processes are important in determining the spectrum of VLF hiss at high altitude. It is also shown that estimated power fluxes inside the electron precipitation region at low altitude might not reach as high levels as observed when the electron beam is weak. In this case, wave propagation outside of the precipitation region will account for the high power flux levels as well as significant magnetic components of VLF hiss observed especially at low altitude. In addition, we show that the transformation of the electron beam in transit to lower altitudes, determined from Liouville's theorem, may influence appreciably VLF hiss power flux spectrum. Finally, it is pointed out that two types of VLF hiss spectrum observed at the ground level can be accounted for by the difference in strength of the electron beam. 相似文献