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排序方式: 共有105条查询结果,搜索用时 15 毫秒
1.
Nicolas Luco Yasuhiro Mori Yosuke Funahashi C. Allin Cornell Masayoshi Nakashima 《地震工程与结构动力学》2003,32(14):2267-2288
Predictors (or estimates) of seismic structural demands that are less computationally time‐consuming than non‐linear dynamic analysis can be useful for structural performance assessment and for design. In this paper, we evaluate the bias and precision of predictors that make use of, at most, (i) elastic modal vibration properties of the given structure, (ii) the results of a non‐linear static pushover analysis of the structure, and (iii) elastic and inelastic single‐degree‐of‐freedom time‐history analyses for the specified ground motion record. The main predictor of interest is an extension of first‐mode elastic spectral acceleration that additionally takes into account both the second‐mode contribution to (elastic) structural response and the effects of inelasticity. This predictor is evaluated with respect to non‐linear dynamic analysis results for ‘fishbone’ models of steel moment‐resisting frame (SMRF) buildings. The relatively small number of degrees of freedom for each fishbone model allows us to consider several short‐to‐long period buildings and numerous near‐ and far‐field earthquake ground motions of interest in both Japan and the U.S. Before doing so, though, we verify that estimates of the bias and precision of the predictor obtained using fishbone models are effectively equivalent to those based on typical ‘full‐frame’ models of the same buildings. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Effects of inertial and kinematic interaction on seismic behavior of pile with embedded foundation 总被引:4,自引:0,他引:4
Kohji Tokimatsu Hiroko Suzuki Masayoshi Sato 《Soil Dynamics and Earthquake Engineering》2005,25(7-10):753-762
Effects of inertial and kinematic forces on pile stresses are studied based on large shaking table tests on pile-structure models with a foundation embedded in dry and liquefiable sand deposits. The test results show that, if the natural period of the superstructure, Tb, is less than that of the ground, Tg, the ground displacement tends to be in phase with the inertial force from the superstructure, increasing the shear force transmitted to the pile. In contrast, if Tb is greater than Tg, the ground displacement tends to be out of phase with the inertial force, restraining the pile stress from increasing. With the effects of earth pressures on the embedded foundation and pile incorporated in, pseudo-static analysis is conducted to estimate maximum moment distribution in pile. It is assumed that the maximum moment is equal to the sum of the two stresses caused by the inertial and kinematic effects if Tb<Tg or the square root of the sum of the squares of the two if Tb>Tg. The estimated pile stresses are in good agreement with the observed ones regardless of the occurrence of soil liquefaction. 相似文献
3.
Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections 总被引:6,自引:0,他引:6
As reported in former studies, temperature observations obtained by expendable bathythermographs (XBTs) and mechanical bathythermographs
(MBTs) appear to have positive biases as much as they affect major climate signals. These biases have not been fully taken
into account in previous ocean temperature analyses, which have been widely used to detect global warming signals in the oceans.
This report proposes a methodology for directly eliminating the biases from the XBT and MBT observations. In the case of XBT
observation, assuming that the positive temperature biases mainly originate from greater depths given by conventional XBT
fall-rate equations than the truth, a depth bias equation is constructed by fitting depth differences between XBT data and
more accurate oceanographic observations to a linear equation of elapsed time. Such depth bias equations are introduced separately
for each year and for each probe type. Uncertainty in the gradient of the linear equation is evaluated using a non-parametric
test. The typical depth bias is +10 m at 700 m depth on average, which is probably caused by various indeterminable sources
of error in the XBT observations as well as a lack of representativeness in the fall-rate equations adopted so far. Depth
biases in MBT are fitted to quadratic equations of depth in a similar manner to the XBT method. Correcting the historical
XBT and MBT depth biases by these equations allows a historical ocean temperature analysis to be conducted. In comparison
with the previous temperature analysis, large differences are found in the present analysis as follows: the duration of large
ocean heat content in the 1970s shortens dramatically, and recent ocean cooling becomes insignificant. The result is also
in better agreement with tide gauge observations.
On leave from the Meteorological Research Institute of the Japan Meteorological Agency. 相似文献
4.
The correlations of the δ18Omax in the shallow ice core from the Guliya ice cap on the Tibetan Plateau with the global sea surface temperatures (SST) and
height at the 500 hPa over the Northern Hemisphere were analyzed. The correlated regions on oceans that have a significant
influence on the δ18Omax in the Guliya ice core are all located in ocean currents, or convergent regions of currents. They are the eastern Equatorial
Pacific, the Northern Pacific Current, the Hot Pool in the eastern Indian Ocean, the Mozambique Current, the Northern Atlantic
Current, the Canary Current and the Atlantic Equatorial Current. The δ18Omax in the Guliya ice core has negative correlations with the SST located in the lower latitudes, and positive correlations with
the SST in the middle latitudes. The correlated areas at the 500 hPa that have a great impact on the δ18Omax are located in the subtropical highs over the mid-low-latitude oceans and the long-wave trough area over Balkhash Lake, where
there are marked negative correlations between the heights in those areas and the δ18Omax. The influencing mechanism is displayed by the diversity of the vapor origins transported to the Guliya region. The strengths
of the European ridge and the ridge over Baikal Lake have notable positive correlations with the δ18Omax. The two systems indirectly influence the vapor transportation towards the Guliya region by the adjustment of long-wave trough
and ridge. 相似文献
5.
The variation of the δ 18O in precipitation and the relationship with precipitation amountat Kyangjin Base House and Yala Glacier Camp in Langtang Valley, Nepal Himalayas were ana-lyzed. The variations of the δ 18O with precipitation had great scatter, and the correlations betweenthe δ18O and precipitation changed with time on the synoptic scale. On the seasonal scale, therewas marked amount effect at Kyangjin Base House. However, the δ18O-precipitation gradient wassmaller than that on the synoptic scale. Because of the maintenance of the basic equilibrium be-tween stable isotopic compositions in atmospheric vapor and precipitation, the evaporation en-richment was light during the rainy season. Therefore, the variation of stable isotopic compositionsin precipitation was independent on the sampling intervals. Simulations show that the rainfall inLangtang Valley was not the outcome of the initial condensation of ocean vapor that originatedfrom low latitudes. The stable isotopic compositions in precipitation were greatly depleted due tothe strong rainout of the vapor from oceans as the vapor was raised over the Himalayas 相似文献
6.
Hakamada Kazuyuki Kojima Masayoshi Tokumaru Munetoshi Ohmi Tomoaki Yokobe Atsushi Fujiki Ken'ichi 《Solar physics》2002,207(1):173-185
Relationships between solar wind speed and expansion rate of the coronal magnetic field have been studied mainly by in-ecliptic observations of artificial satellites and some off-ecliptic data by Ulysses. In this paper, we use the solar wind speed estimated by interplanetary scintillation (IPS) observations in the whole heliosphere. Two synoptic maps of SWS estimated by IPS observations are constructed for two Carrington rotations CR 1830 and 1901; CR 1830 starting on the 11th of June, 1990 is in the maximum phase of solar activity cycle and CR 1901 starting on the 29th of September, 1995 is in the minimum phase. Each of the maps consist of 64800 (360×180) data points. Similar synoptic maps of expansion rate of the coronal magnetic field (RBR) calculated by the so-called potential model are also constructed under a radial field assumption for CR 1830 and CR1901. Highly significant correlation (r=–0.66) is found between the SWS and the RBR during CR1901 in the solar minimum phase; that is, high-speed winds emanate from photospheric areas corresponding to low expansion rate of the coronal magnetic field and low speed winds emanate from photospheric areas of high expansion rate. A similar result is found during CR 1830 in solar maximum phase, though the correlation is relatively low (r=–0.29). The correlation is improved when both the data during CR 1830 and CR 1901 are used together; the correlation coefficient becomes –0.67 in this case. These results suggest that the correlation analysis between the SWS and the RBR can be applied to estimate the solar wind speed from the expansion rate of the coronal magnetic field, though the correlation between them may depend on the solar activity cycle. We need further study of correlation analysis for the entire solar cycle to get an accurate empirical equation for the estimation of solar wind speed. If the solar wind speed is estimated successfully by an empirical equation, it can be used as an initial condition of a solar wind model for space weather forecasts. 相似文献
7.
Masayoshi Yokosawa 《Astrophysics and Space Science》1986,119(1):213-215
A mechanism is proposed for the formation of collinated beams in radio galaxies. Collimated flows are considered to be non-thermally driven by high energy particles and magneto-hydrodynamic (MHD) waves. The galactic nucleus is regarded as being surrounded by a cool gas. The cool gas accretes onto the nucleus, and then the high energy particles are completely locked to the MHD waves. When a quasi-radial magnetic field is embedded in the accretion flow, the resulting MHD wave packets are collimated into the direction of the symmetry axis of the galactic nuclear disc. The fluid around the nucleus is considered to be accelerated and heated by these MHD waves. The fluid beam is ejected along the symmetry axis.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
8.
Real-time multi-model decadal climate predictions 总被引:1,自引:1,他引:0
Doug M. Smith Adam A. Scaife George J. Boer Mihaela Caian Francisco J. Doblas-Reyes Virginie Guemas Ed Hawkins Wilco Hazeleger Leon Hermanson Chun Kit Ho Masayoshi Ishii Viatcheslav Kharin Masahide Kimoto Ben Kirtman Judith Lean Daniela Matei William J. Merryfield Wolfgang A. Müller Holger Pohlmann Anthony Rosati Bert Wouters Klaus Wyser 《Climate Dynamics》2013,41(11-12):2875-2888
We present the first climate prediction of the coming decade made with multiple models, initialized with prior observations. This prediction accrues from an international activity to exchange decadal predictions in near real-time, in order to assess differences and similarities, provide a consensus view to prevent over-confidence in forecasts from any single model, and establish current collective capability. We stress that the forecast is experimental, since the skill of the multi-model system is as yet unknown. Nevertheless, the forecast systems used here are based on models that have undergone rigorous evaluation and individually have been evaluated for forecast skill. Moreover, it is important to publish forecasts to enable open evaluation, and to provide a focus on climate change in the coming decade. Initialized forecasts of the year 2011 agree well with observations, with a pattern correlation of 0.62 compared to 0.31 for uninitialized projections. In particular, the forecast correctly predicted La Niña in the Pacific, and warm conditions in the north Atlantic and USA. A similar pattern is predicted for 2012 but with a weaker La Niña. Indices of Atlantic multi-decadal variability and Pacific decadal variability show no signal beyond climatology after 2015, while temperature in the Niño3 region is predicted to warm slightly by about 0.5 °C over the coming decade. However, uncertainties are large for individual years and initialization has little impact beyond the first 4 years in most regions. Relative to uninitialized forecasts, initialized forecasts are significantly warmer in the north Atlantic sub-polar gyre and cooler in the north Pacific throughout the decade. They are also significantly cooler in the global average and over most land and ocean regions out to several years ahead. However, in the absence of volcanic eruptions, global temperature is predicted to continue to rise, with each year from 2013 onwards having a 50 % chance of exceeding the current observed record. Verification of these forecasts will provide an important opportunity to test the performance of models and our understanding and knowledge of the drivers of climate change. 相似文献
9.
This paper presents a test system for conducting on-line tests in a real time and a series of real-time on-line tests conducted to verify the effectiveness of the system. The proposed system is characterized by (1) use of a Digital Signal Processor (DSP) now readily available, (2) adoption of the C language to ensure easy programming, and (3) separation of response analysis and displacement signal generation to apply the system for tests with complex structures. To create displacement signals successively without being interrupted by the computation of equations of motion, extrapolation and interpolation procedures using present and past target displacements are developed. Base-isolated building models were chosen for the real-time on-line test. The effectiveness of the extrapolation and interpolation procedures was demonstrated through a series of real-time on-line tests applied to the models treated as SDOF structures. A five-storey base-isolated building model (treated as a six DOF structure) was tested for various ground motions, and it was verified that the system is able to simulate earthquake responses involving large displacements and large velocities. The number of DOFs that can be handled in the proposed system was investigated, and it was found that the system is capable of performing the test with reasonable accuracy for up to 10 DOF structures with a range of response frequency not greater than 3·0 Hz, or 12 DOF structures with a range of response frequency not greater than 2·0 Hz. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
10.
Earthquake engineering research and development have received much attention since the first half of the twentieth century. This valuable research presented a huge step forward in understanding earthquake hazard mitigation, which resulted in appreciable reduction of the effects of past earthquakes. Nevertheless, the 2011 Tohoku earthquake and the subsequent tsunami resulted in major damage. This paper presents the timeline of earthquake mitigation and recovery, as seen by the authors. Possible research directions where the authors think that many open questions still remain are identified. These are primarily based on the important lessons learned from the 2011 Tohoku earthquake. 相似文献