排序方式： 共有38条查询结果，搜索用时 46 毫秒
31.
A semi-analytical boundary element method is developed for the efficient time-domain dynamic response analysis of a finitely long cylindrical cavity with an arbitrary cross-section geometry. High computational efficiency is achieved by mapping a complex shape of the cross-section into a circular shape. For this purpose a special coordinate transformation equation is presented. This mapping enables us to discretize the boundary element equation only along the longitudinal axis of the cavity. The versatility and accuracy of the method are amply demonstrated through a number of examples. The transient stresses and displacements are found to be considerably influenced by the slenderness ratio, length over diameter of the cavity and the incidence angle of the incident wave. 相似文献
32.
The horizontal earthquake induced hydrodynamic pressure acting on the surface of axisymmetric offshore and coastal structures is explored. A semi-analytical and semi-numerical approach based on the use of a complete and non-singular set of Trefftz functions is developed. Using this method, one can model accurately the compressibility of the sea water and gravity waves on the water surface. The proposed method shows a relatively simple and efficient approach. This is because the number of degrees of freedom in the matrix equation depends only on the number of selected Trefftz functions and because the discretization of the fluid domain into boundary elements is restricted to the structural surface only. This method is also easy to apply in engineering analysis of hydrodynamic pressure induced by an actual earthquake acceleration. Numerical examples are presented to illustrate the results obtained from this method. Several special interesting topics, such as the effects of the water compressibility, the gravity waves on the water surface and the geometrical shape of the structural surface, are also discussed. 相似文献
33.
The Domain, where the necessary and sufficient conditions for the existence of the KdV-type solitary Rossby waves are satisfied is defined in the shallow water β-plane model. The KdV-type solitary Rossby waves are the Rossby waves whose time-longitude dependence is determined by the KdV equation. As far as an appropriate amplitude and an appropriate ratio of the scales of the east-west and north-south directions are given, the KdV-type solitary Rossby waves can exist for every basic zonal flow. This result suggests the large validity of the soliton model in geophysical fluid dynamics. The KdV-type solitary Rossby waves are classified into four categories: (1) shear solitons studied by Long, Larsen, Benny, Redekop, and Hukuda, (2) β-divergent solitons studied by Clarke, Yamagata, and Nogami, (3) β-solitons found in the case of the strong stratification, and (4) divergent solitons which exist in the planetary-geostrophic-scale zonal flow. A remarkable result is that, in addition to the conventional east-west elongated solitons, the north-south elongated solitons can also exist for the case of the divergent solitons. 相似文献
34.
Deep-sea sediment cores ranging up to 30,000–80,000 yrs in age were taken from a southern region of the Japan Sea and subjected to analyses for 5 major and 11 trace elements by means of instrumental photon activation analysis with 30 MeV bremsstrahlung. These elements were Ca, Fe, Mg, Na, Ti, Ba, Ce, Co, Cr, Mn, Nb, Ni, Rb, Sr, Y and Zr. Additionally, Al was determined spectrophotometrically. Distribution patterns of these elements with depth in the sediment columns were derived. Enrichments of Ca and Sr by biogenous process were observed; these Ca maxima are well correlated with Mn maxima. Below the Holocene—Pleistocene boundary, continuous transportation of poorly degraded continental debris, which was low in metallic constituents, was noted. A distinct enrichment of the top layer of the sediments in Mn was observed. This is the result of post-depositional upward migration of Mn. Fe, Co and Ni were also enriched in the top layers. In the central part of the basin, the oxidized post-glacial zone appears to be a typical pelagic sediment. 相似文献
35.
The resistance of a soil layer to steady horizontal vibration of an elastic pile is theoretically investigated. The pile is assumed to be vertical and of circular cross-section. The soil is modelled as a linear viscoelastic layer with hysteretic material damping. A closed form solution is obtained for the resistance of the soil layer to the motion. This resistance depends on shear modulus of soil, frequency, pile slenderness, material damping and Poisson's ratio. A parametric study of the effect of these parameters is included. The soil layer resistance is expressed in a form which can be used directly in the solution of the soil-pile interaction problem which is treated in a subsequent paper. The approach also applies for rigid deeply embedded footings. 相似文献
36.
This review article is intended to introduce periglacial environment present and past in Japan, and to summarize some studies on it. The periglacial climate in Japan is characterized by a wide annual range of air temperature and much snow accumulation in winter. This makes for local variability in appearance of periglacial processes on the mountain slopes near crests. In Japan, the main interest in periglacial studies concerns the above-mentioned variability and its causes, that is, how periglacial processes relate to vegetation, local climate especially snow accumulation and its seasonal duration, soil, micro-relief, properties of bed rock etc.Seasonal soil freezing was measured in lowlands of Hokkaido. Depth of frost penetration without snow cover increases proportionally to the increments of accumulated degree-days. Depth of frost penetration on natural conditions is affected not only by the degree-days but also by the depth of snow cover which differs locally even within a small area.The oldest frozen ground phenomena was recognized in a horizon about 50,000 years old in the lowlands of Hokkaida. Involutions about 40,000 years ago exceeded active earth hummocks in size. And the phenomena reached the maximum phase is represented by icewedge casts of the En-a pumice (ca. 15,000 abp). Most of fossil features are covered with undisturbed Ta-d pumice (cz. 9,000 abp), but earth hummocks and vertical stones have been still formed in the Holocene tephra layers. 相似文献
37.
Hiroyuki Yamada Futoshi Nakamura Yasuharu Watanabe Marie Murakami Takeshi Nogami 《水文研究》2005,19(13):2507-2524
Permeability of a streambed is an important factor regulating nutrient and oxygen availability for aquatic biota. In order to investigate the relationship, an accurate permeability should be measured. However, it is difficult to measure permeability in a coarse gravel bed using a conventional permeability test. Moreover, turbulent flow may occur in coarse bed material, and then deviations from Darcy's law do occur. Thus, permeability calculated following Darcy's law may be overestimated under turbulent flow conditions and should be corrected. The packer test can be used in highly permeable gravel beds. We developed a field method applicable to a gravel bed using the packer test and derived an equation adopting a law of turbulent flow to study the problems under any type of flow condition. The accuracy of the equation was examined using a laboratory flume with a gravel bed. The results suggested that permeability calculated from Hvorslev's equation is overestimated for turbulent flow. In contrast, our equation, developed here, could evaluate permeability accurately under any type of flow condition. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
38.
We estimate the economic value of the natural environment damaged in the Seto Inland Sea after the introduction of the Law on Temporary Measures for the Environmental Conservation of the Seto Inland Sea (Setouchi Law) and the value of the natural environment that survived, using a Contingent Valuation (CV) survey on an Internet web site. The CV survey contains three plans. Plan 1 is to restore 4 ha of reclaimed land. By estimating the Willingness To Pay (WTP) for plan 1, we can appraise the value of the natural environment that was damaged as a result of the original reclamation. Plan 2 is to transplant Zostera (eel-grass) into an area of 10 ha offshore. Plan 3 is to preserve the shore area, a natural habitat for rare animal species, under the National Trust Program. From the WTP for plans 2 and 3, we can estimate the value of the shore area and the areas a little farther offshore. The value of the natural environment damaged in the Seto Inland Sea as a result of reclaiming projects after the introduction of the Setouchi Law and the value of the existing natural environment of the Seto Inland Sea from the WTP for the plans were estimated to about 172 trillion yen (1.46 trillion dollars) and about 424 trillion yen (3.60 trillion dollars), respectively. The results indicate that in the 25 years since the introduction of the Setouchi Law, we have degraded every year about 6.88 trillion yen (58.5 billion dollars) worth of the natural environment by reclaiming. Some seaweed farms and natural shore areas, natural habitats to rare marine life-forms like the horseshoe crab and the fiddler crab have survived, but their value amounts to about 80% of Japan's GDP. 相似文献