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排序方式: 共有142条查询结果,搜索用时 15 毫秒
111.
Kazuhiko Yamada 《地震工程与结构动力学》2000,29(8):1199-1217
A control strategy is proposed for variable damping elements (VDEs) used together with auxiliary stiffness elements (ASEs) that compose a time‐varying non‐linear Maxwell (NMW) element, considering near‐future excitation influence. The strategy first composes a state equation for the structural dynamics and the mechanical balance in the NMW elements. Next, it establishes a cost function for estimating future responses by the weighted quadratic norms of the state vector, the controlled force and the VDEs' damping coefficients. Then, the Euler equations for the optimum values are introduced, and also approximated by the first‐order terms under the autoregressive (AR) model of excitation information. Thus, at each moment tk, the strategy conducts the following steps: (1) identify the obtained seismic excitation information to an AR model, and convert it to a state equation; and (2) determine VDEs' damping coefficients under the initial conditions at tk and the final state at tk+L, using the first‐order approximation of the Euler equations. The control effects are examined by numerical experiments. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
112.
Jidapa Koomklang Hitomi Yamaguchi Kazuhiko Ichimi Kuninao Tada 《Journal of Oceanography》2018,74(1):13-21
A superficial sediment layer (SL) is the top 2–3 mm layer of surface sediment that may contribute to high upward nutrient flux. To study the characteristics and the biogeochemical processes in the superficial layer, the seasonal variation in the total phytopigments (chlorophyll a and pheo-pigments), total organic carbon (TOC), and total nitrogen (TN) of the surface sediments in a shallow coastal area, Shido Bay, were measured, and the influence of the superficial sediment layer on nutrient flux at the sediment–water interface was investigated. TOC and TN content were relatively constant for the SL and subsurface layers (0–1 and 1–2 cm) during the study period. In contrast, total phytopigments content was higher in the SL layer than in the subsurface layers. The results of upward nutrient flux experiments showed higher nutrient release within the whole sediment core (SL remaining) than the SL-less (SL removed) core. Moreover, high nutrient fluxes were observed during the high temperature season, indicating that seasonal variation in nutrient flux was regulated by temperature. Moreover, in the low temperature season, the SL seemed to absorb nutrients, probably because of microphytobenthos photosynthesis that took up the nutrients under the sufficient light penetration to the sea floor. 相似文献
113.
Akihiro Iwase Kazuhiko Sakai Atsushi Suzuki Robert van Woesik 《Estuarine, Coastal and Shelf Science》2008,77(4):672-678
We tested the hypothesis that foliose plates of Echinopora lamellosa (Esper, 1795) adjust their primary growth direction (or slope from the horizontal) when irradiance (light) is limiting. This hypothesis was tested at a coral-reef locality that is shaded daily by steep adjacent hills, restricting direct light to only a few hours each day (Iwayama Bay, Palau). The angle at which colonies received maximum light was measured using acetate film, and was compared with modeled estimates (using a simple global-light model). We show strong relationships between light and primary-colony gradients; with the foliose plates acting as parabolic antennae, predictably adjusting their primary gradients to optimize light capture. 相似文献
114.
Kazuhiko Yamada 《地震工程与结构动力学》1999,28(12):1587-1599
This paper examines a real-time prediction method, aimed at application in active structural control. The examined method applies preceding seismic excitation information at a certain moment to a time-variant AutoRegressive (AR) model and uses it to predict near-future excitation information. The performances of this method and appropriate identification parameters are examined by numerical experiments. In fact, the results of these experiments show that a time-variant AR model with appropriate identification parameters has little change in low-frequency components despite change in AR coefficients. The performance of a fixed-coefficient AR model is thus examined. The results show that even a fixed-coefficient AR model can sufficiently predict 0·05-s-future excitation information. Copyright © 1999 John Wiley & Sons Ltd. 相似文献
115.
The mechanism of a characteristic sea level response (barotropic coastal ocean response) to wind field fluctuation around
the tip of the Izu Peninsula observed during the middle of December 2000 to the middle of January 2001 was investigated based
on three types of numerical experiments using the Princeton Ocean Model with various parameters. The response was characterized
by the relaxation of sea level falling (rising) during eastward upwelling (westward downwelling) favorable wind regime. Analyses
of quasi-realistic numerical model results in terms of the vertically integrated momentum balances and vorticity balance for
the barotropic mode revealed that: 1) development/abatement of two anomalous circulations generated around the tip of the
Izu Peninsula controls the sea level response through the acceleration/deceleration of a quasi-geostrophic barotropic coastal
current between the circulations; 2) nonlinear vorticity advection by the Kuroshio Current and by the coastal current, coupled
with vorticity diffusion, decelerates the quasi-geostrophic coastal current in the latter half of the wind regimes, which
induces the relaxation of sea level rise/fall. The results of the quasi-realistic numerical experiment suggest that an analysis
of the vorticity balance for the barotropic mode contributes to a better understanding of sea level responses to wind in coastal
regions with strong currents and complex topography. In addition, a numerical experiment with idealized spatially uniform
density stratification and a quasi-realistic wind field shows that if the Kuroshio Current had been shifted far offshore from
the Izu Peninsula during the observation period, westward propagating continental shelf waves would have controlled the coastal
sea level response. 相似文献
116.
Hajime Kawakami Makio C. Honda Kazuhiko Matsumoto Tetsuichi Fujiki Shuichi Watanabe 《Journal of Oceanography》2010,66(1):71-83
Observations of primary productivity, 234Th, and particulate organic carbon (POC) were made from west to east across the northern North Pacific Ocean (from station
K2 to Ocean Station Papa) during September–October 2005. Primary productivities in this region varied longitudinally from
approximately 236 to 444 mgC m−2d−1 and clearly indicate the West High East Low (WHEL) trend. We estimated east-west variations in the POC flux from the surface
layer (0–100 m) by using 234Th as a tracer. POC fluxes in the western region (44–53 mgC m−2d−1) were higher than those in the eastern region (21–34 mgC m−2d−1). However, the export ratios (e-ratios) ranged from approximately 8% to 16% and did not show the WHEL trend. Contrary to our expectation, no relation between
POC flux (or e-ratio) and diatom biomass (or dominance) was apparent in autumn in the northern North Pacific. 相似文献
117.
Kazuhiko Yamada 《地震工程与结构动力学》2000,29(4):545-554
A simple non‐linear control law is proposed for reducing structural responses against seismic excitations. This law defines control force dynamics by one differential equation involving a non‐linear term that restrains the control force amplitude. If non‐linearity is neglected, the control force becomes the force in a Maxwell element, so it is called the non‐linear‐Maxwell‐element‐type (NMW) control force. The NMW control force vs. deformation relation plots hysteretic curves. The basic performance of an SDOF model with the NMW control force is examined for various conditions by numerical analyses. Furthermore, the control law is extended to fit an MDOF structural model, and an application example is shown. The computational results show that the NMW control force efficiently reduces structural responses. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
118.
Toshimi Satoh Masanori Horike Yoshihiro Takeuchi Tomiichi Uetake Hideyo Suzuki 《地震工程与结构动力学》1997,26(8):781-795
We evaluate the non-linear behaviour of soil sediments, analysing five weak and four strong motions observed at depths of 1 m and 28 m, in eastern Shizuoka prefecture, Japan. We identify S-wave velocities and frequency-dependent damping factors by minimizing the residual between observed and theoretical spectral ratios, based on a linear one-dimensional model. We find that S-wave velocities identified from strong motions, whose peak ground acceleration are 440, 210, 176, and 140 cm/s2, are significantly smaller than those identified from weak motions. The shear modulus reduction ratios estimated from identified S-wave velocities become clear above an effective shear strain of 10-4 and agree with laboratory test results below an effective shear strain of 8×10-4. The differences of damping factors between weak and strong motions are not clear below this effective shear strain, as the laboratory test suggested. The equivalent linear one-dimensional model, with frequency-dependent damping factors, is confirmed to be valid to simulate strong motions at least an effective shear strain of less than 4×10-4. © 1997 John Wiley & Sons, Ltd. 相似文献
119.
Variation of dissolved organic matter and fluorescence characteristics before,during and after phytoplankton bloom 总被引:3,自引:0,他引:3
Marut Suksomjit Seiya Nagao Kazuhiko Ichimi Tatsuo Yamada Kuninao Tada 《Journal of Oceanography》2009,65(6):835-846
The variation of dissolved organic matter (DOM) and fluorescence characteristics during the phytoplankton bloom were investigated
in Yashima Bay, at the eastern part of the Seto Inland Sea, Japan. We found significant accumulations of dissolved organic
carbon (DOC), dissolved organic nitrogen (DON), chromophoric dissolved organic matter (CDOM) fluorescence, and UV260 during the phytoplankton bloom period in 2005, although lower accumulations of DOC and DON and only increases of CDOM fluorescence
were observed during the bloom period in 2006. Little or no correlation between DOM and phytoplankton abundance might be due
to the composition of DOM, which is a complex mixture of organic materials. The 3D-EEM results revealed that the DOM produced
around the phytoplankton bloom period contained tyrosine, tryptophan, and humic-like substances. Our results showed that the
occurrence of phytoplankton bloom contributed to the production of DOM in coastal water but the DOM accumulation depended
on the type of phytoplankton bloom, the phytoplankton species in particular. From our results, we concluded that phytoplankton
have a great role in the dynamics of DOM as a producer in a coastal environment. 相似文献
120.