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931.
Influence of the mean period of ground motion on the inelastic dynamic response of single and multi degree of freedom systems 总被引:1,自引:0,他引:1
This paper focuses on examining the effects of frequency content of the ground motion on the inelastic demands imposed on both single degree of freedom (SDF) and multi degree of freedom (MDF) steel‐framed systems. A detailed literature review is conducted to identify the indicator that best represents the frequency content of ground motion. The mean period (Tm) of ground motion is selected owing to its ability to distinguish between various spectral shapes of ground motion, and its relationship with magnitude, distance and site characteristics. Inelastic displacement demands on SDF systems for target ductility levels are first studied in the light of Tm, using a suite of 128 ground motion records. The study is then extended to MDF systems with the help of incremental dynamic analysis by employing the same ground motion ensemble to assess the influence of Tm on various engineering demand parameters. The results obtained indicate that, for SDF systems, the amplification of displacements occurs when the period ratio between elastic period (Te) and Tm is lower than unity. For MDF systems, the results demonstrate that the influence of higher modes on the base shear and maximum storey drift profile becomes more pronounced, as Tm approaches the higher mode periods of the structure. These observations, for both SDF and MDF systems, tend to be more evident for higher levels of inelasticity. The significance of the results, with particular reference to European seismic design procedures, is highlighted. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
932.
Wet and dry spell analysis of Global Climate Model-generated precipitation using power laws and wavelet transforms 总被引:2,自引:2,他引:0
Ashok K. Mishra Mehmet ?zger Vijay P. Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(4):517-535
Climate model simulations for the twenty-first century point toward changing characteristics of precipitation. This paper
investigates the impact of climate change on precipitation in the Kansabati River basin in India. A downscaling method, based
on Bayesian Neural Network (BNN), is applied to project precipitation generated from six Global Climate Models (GCMs) using
two scenarios (A2 and B2). Wet and dry spell properties of monthly precipitation series at five meteorologic stations in the
Kansabati basin are examined by plotting successive wet and dry durations (in months) against their number of occurrences
on a double-logarithmic paper. Straight-line relationships on such graphs show that power laws govern the pattern of successive
persistent wet and dry monthly spells. Comparison of power-law behaviors provides useful interpretation about the temporal
precipitation pattern. The impact of low-frequency precipitation variability on the characteristics of wet and dry spells
is also evaluated using continuous wavelet transforms. It is found that inter-annual cycles play an important role in the
formation of wet and dry spells. 相似文献
933.
Devendraa Siingh R. P. Singh Ashok K. Singh M. N. Kulkarni A. S. Gautam Abhay K. Singh 《Surveys in Geophysics》2011,32(6):659-703
The physics of solar forcing of the climate and long term climate change is summarized, and the role of energetic charged
particles (including cosmic rays) on cloud formation and their effect on climate is examined. It is considered that the cosmic
ray-cloud cover hypothesis is not supported by presently available data and further investigations (during Forbush decreases
and at other times) should be analyzed to further examine the hypothesis. Another player in climate is lightning through the
production of NOx; this greenhouse gas, water vapour in the troposphere (and stratosphere) and carbon dioxide influence the global temperature
through different processes. The enhancement of aerosol concentrations and their distribution in the troposphere also affect
the climate and may result in enhanced lightning activity. Finally, the roles of atmospheric conductivity on the electrical
activity of thunderstorms and lightning discharges in relation to climate are discussed. 相似文献
934.
A first-order seismotectonic model was created for South Africa. This was done using four logical steps: geoscientific data
collection, characterisation, assimilation and zonation. Through the definition of subunits of concentrations of earthquake
foci and large neotectonic and structural domains, seismotectonic structures, systems and domains were created. Relatively
larger controls of seismicity exist between the Great Escarpment and the coast. In the south, this region is characterised
by large aeromagnetic anomalies and large EW trending faults. In the west, it is characterised by the NW–SE trending Wegener
stress anomaly, radial-trending dykes and earthquake clusters. In the east, it is characterised by a large neotectonic domain
where several large historical earthquakes occurred. In the centre of South Africa, several clusters of earthquake activity
are found, often related to mining activity. Further north, seismicity is related to both mining activity and neotectonic
deformation. This work contributes to the development of a seismotectonic model for South Africa by (1) bringing together,
digitally, several data sets in a common GIS platform (geology, geophysics, stress, seismicity, neotectonics, topography,
crustal and mantle structure and anisotropy), (2) understanding the significance of data sets for seismotectonic zonation
and limitations thereof and (3) obtaining a reasonable regional model for use in seismic hazard assessments. 相似文献
935.
Impact of satellite soundings on the simulation of heavy rainfall associated with tropical depressions 总被引:1,自引:1,他引:0
The present study is carried out to examine the impact of temperature and humidity profiles from moderate resolution imaging
spectroradiometer (MODIS) or/and atmospheric infrared sounder (AIRS) on the numerical simulation of heavy rainfall events
over the India. The Pennsylvania State University–National Centre for Atmospheric Research fifth-generation mesoscale model
(MM5) and its three-dimensional variational (3D-Var) assimilation technique is used for the numerical simulations. The heavy
rainfall events occurred during October 26–29, 2005, and October 27–30, 2006, were chosen for the numerical simulations. The
results showed that there were large differences observed in the initial meteorological fields from control experiment (CNT;
without satellite data) and assimilation experiments (MODIS (assimilating MODIS data), AIRS; (assimilating AIRS data); BOTH
(assimilating MODIS and AIRS data together)). The assimilation of satellite data (MODIS, AIRS, and BOTH) improved the predicted
thermal and moisture structure of the atmosphere when compared to CNT. Among the experiments, the predicted track of tropical
depressions from MODIS was closer to the observed track. Assimilation of MODIS data also showed positive impact on the spatial
distribution and intensity of predicted rainfall associated with the depressions. The statistical skill scores obtained for
different experiments showed that assimilation of satellite data (MODIS, AIRS, and BOTH) improved the rainfall prediction
skill when compared to CNT. Root mean square error in quantitative rainfall prediction is less in the experiment which assimilated
MODIS data when compared to other experiments. 相似文献
936.
We present the seismic energy, strain energy, frequency–magnitude relation (b-value) and decay rate of aftershocks (p-value) for the aftershock sequences of the Andaman–Sumatra earthquakes of December 26, 2004 (M
w 9.3) and March 28, 2005 (M
w 8.7). The energy released in aftershocks of 2004 and 2005 earthquake was 0.135 and 0.365% of the energy of the respective
mainshocks, while the strain release in aftershocks was 39 and 71% for the two earthquakes, respectively. The b-value and p-value indicate normal value of about 1. All these parameters are in normal range and indicate normal stress patterns and
mechanical properties of the medium. Only the strain release in aftershocks was considerable. The fourth largest earthquake
in this region since 2004 occurred in September 2007 off the southern coast of Island of Sumatra, generating a relatively
minor tsunami as indicated by sea level gauges. The maximum wave amplitude as registered by the Padang, tide gauge, north
of the earthquake epicenter was about 60 cm. TUNAMI-N2 model was used to investigate ability of the model to capture the minor
tsunami and its effect on the eastern Indian Coast. A close comparison of the observed and simulated tsunami generation, propagation
and wave height at tide gauge locations showed that the model was able to capture the minor tsunami phases. The directivity
map shows that the maximum tsunami energy was in the southwest direction from the strike of the fault. Since the path of the
tsunami for Indian coastlines is oblique, there were no impacts along the Indian coastlines except near the coast of epicentral
region. 相似文献
937.
The Indus flood of 2010 in Pakistan: a perspective analysis using remote sensing data 总被引:1,自引:1,他引:0
The Indus flood in 2010 was one of the greatest river disasters in recent history, which affected more than 14 million people
in Pakistan. Although excessive rainfall between July and September 2010 has been cited as the major causative factor for
this disaster, the human interventions in the river system over the years made this disaster a catastrophe. Geomorphic analysis
suggests that the Indus River has had a very dynamic regime in the past. However, the river has now been constrained by embankments
on both sides, and several barrages have been constructed along the river. As a result, the river has been aggrading rapidly
during the last few decades due to its exceptionally high sediment load particularly in reaches upstream of the barrages.
This in turn has caused significant increase in cross-valley gradient leading to breaches upstream of the barrages and inundation
of large areas. Our flow accumulation analysis using SRTM data not only supports this interpretation but also points out that
there are several reaches along the Indus River, which are still vulnerable to such breaches and flooding. Even though the
Indus flood in 2010 was characterized by exceptionally high discharges, our experience in working on Himalayan rivers and
similar recent events in rivers in Nepal and India suggest that such events can occur at relatively low discharges. It is
therefore of utmost importance to identify such areas and plan mitigation measures as soon as possible. We emphasize the role
of geomorphology in flood analysis and management and urge the river managers to take urgent steps to incorporate the geomorphic
understanding of Himalayan rivers in river management plans. 相似文献
938.
A DEM-based evaluation of potential flood risk to enhance decision support system for safe evacuation 总被引:2,自引:1,他引:1
A practical, DEM-based practical method is proposed to enhance flood risk management in fluvial areas by quantifying relative
risk as a function of vulnerability to inland and evacuation difficulty. Both measures are based mainly on the topography
of the region, so the method does not require detailed data on the physical characteristics of the land. First, we use the
deterministic 8-node method on a digital elevation map (DEM) to trace storm waterways. Second, we repeat the process on a
reversed DEM to trace evacuation routes that avoid the waterways and zones dangerously close to the rivers. Finally, on the
basis of such two flow lines of evacuee and storm water, we proposed the protocol to evaluate the flood risk at every point
on the map taking into account both the minimum time required for floodwater to arrive and duration of an evacuation from
that location. The time that must be allocated for safe evacuation is defined as the potential flood risk of evacuation (PFRE).
The method is demonstrated on a fluvial area of the Kaki River in Nagaoka city, Japan. In addition, we illustrated the application
of the PFRE map to divide the region into areas of greater or lesser evacuation urgency. 相似文献
939.
P. V. Hareesh Kumar A. Raghunadha Rao K. Anilkumar M. Padmanabham K. G. Radhakrishnan 《Natural Hazards》2011,57(3):643-656
Analysis of the time series data collected from a stationary location in the continental shelf of the southeastern Arabian
Sea during different month indicated prominent internal wave (IW) activity. Time evolution of temperature, resolved using
Morlet wavelet technique, revealed that maximum energy was concentrated in the diurnal band at the density interface, whereas
within the interior of thermocline, the dominant energy concentration shifted to semi-diurnal band. Both these harmonics have
maximum amplitude (>15 m) during the pre-monsoon and monsoon season when the water column was highly stratified (>0.05 kg/m4), but they were not discernable in the temperature record when the stratification was weak (i.e., especially during winter).
An acoustic propagation model based on ray theory, Bellhop (http:/oalib.hlsresearch.com/modes/acoustictoolbox/at.zip) was
utilized to compute the transmission loss (TL) associated with the passage of low-frequency IWs. The TL was computed using
the model considering (1) range-dependent and range-independent environmental scenario and (2) for different source and receiver
depth configurations. Intermittent fading of acoustic signals was observed in the presence of IW. It was also observed that
fading of signals very much depends on the source–receiver configuration. 相似文献
940.
Suhas SHETYE Rahul MOHAN Sunil Kumar SHUKLA Sudhakar MARUTHADU Rasik RAVINDRA 《《地质学报》英文版》2011,85(3):549-558
Kongsfjorden is a fjord in Spitsbergen (Svalbard archipelago) that lies adjacent to both Arctic and Atlantic water masses and is therefore a suitable site to understand the effects of climate change on ecosystems. To decipher the effect of the lateral advection of transformed Atlantic water (TAW) within the fjord, spatial variations of foraminiferal tests, their test size variations and stable isotopic composition (δ13C and δ18O) in the surface sediments were studied. Total organic carbon and textural analyses were also carried out. The dominant benthic foraminifera included Nonionellina labradorica, Elphidium excavatum, Cassidulina reniforme, Quinqueloculina stalkeri and Islandiella islandica. Nonionellina labradorica was the predominant species in the outer fjord, whereas Elphidium excavatum and Cassidulina reniforme were dominant in the inner fjord. Total organic carbon and the test size of Nonionellina labradorica within the fjord were highly correlated (r2?=?0.97) and both showed a decreasing trend towards the inner fjord. Based on the distribution and abundance of Nonionellina labradorica as well as temperature profiles, we suggest that there was little or no major change in the lateral advection of TAW within the fjord in the immediate past. 相似文献