排序方式： 共有43条查询结果，搜索用时 15 毫秒
31.
A new method is presented for the determination of the parameters of the pulse contained in pulse‐like records. The Mavroeidis and Papageorgiou (M&P) wavelet is used for the mathematical representation of the pulse, but the proposed methodology could be modified to cover other types of wavelets as well. First, the period of the pulse is determined from the peak of the Sd × Sv product spectrum, a new concept that is introduced herein and is defined as the product of the velocity and the displacement response spectra. The remaining parameters of the M&P wavelet are derived from the targeted response spectrum of the ground motion applying a new relationship that is established between the cumulative absolute displacement (CAD) of a wavelet and its peak spectral amplitude. The method follows a well‐defined procedure that can be easily implemented in a computer code for the automatic determination of the pulse parameters of a given ground motion. As an application, the pulses contained in 91 NGA records that have been classified as pulse‐like by Baker are determined. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
32.
33.
Spatial seismic modeling of base‐isolated buildings pounding against moat walls: effects of ground motion directionality and mass eccentricity 
下载免费PDF全文
下载免费PDF全文 Structural impact between adjacent buildings may induce local and, in some extreme cases, severe damage, especially in the case of seismically isolated buildings. This study parametrically investigates in the three‐dimensional domain the effect of pounding on the peak response of base‐isolated buildings, which are simulated as nonlinear three‐dimensional multi‐degree‐of‐freedom systems. Firstly, it is shown that considering unidirectional, instead of bidirectional, excitations may lead to underestimation of the base drift demands. Subsequently, the peak responses of seismically isolated buildings utilizing lead rubber bearings are studied while varying important parameters, such as the incidence angle of seismic excitations, the available seismic clearance, and mass eccentricities, under the action of bidirectional horizontal excitations. A large number of numerical simulations are performed using a specially developed software that implements an efficient approach to model impacts, taking into account arbitrary locations of contact points. It is found that the peak interstory drift ratio is significantly influenced by the directionality of the ground motion. Therefore, the seismic performance of structures should ideally be assessed examining the peak structural response while bidirectional ground motions are imposed at various incident angles. Furthermore, it is also observed that the interstory drift ratios increase while decreasing the available gap size, up to a certain value. Finally, the parametric analyses indicate that the effects of impact are more severe for structures with mass eccentricities, and in which case, the estimation of the critical incidence angle becomes more laborious. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
34.
George Papaioannou George Varlas Anastasios Papadopoulos Athanasios Loukas Petros Katsafados Elias Dimitriou 《水文研究》2021,35(4):e14151
A common source of uncertainty in flood inundation forecasting is the hydrograph used. Given the role of sea-air-hydro-land chain processes on the water cycle, flood hydrographs in coastal areas can be indirectly affected by sea state. This study investigates sea-state effects on precipitation, discharge, and flood inundation forecasting implementing atmospheric, ocean wave, hydrological, and hydraulic-hydrodynamic coupled models. The Chemical Hydrological Atmospheric Ocean wave System (CHAOS) was used for coupled hydro-meteorological-wave simulations ‘accounting’ or ‘not accounting’ the impact of sea state on precipitation and, subsequently, on flood hydrograph. CHAOS includes the WRF-Hydro hydrological model and the WRF-ARW meteorological model two-way coupled with the WAM wave model through the OASIS3-MCT coupler. Subsequently, the 2D HEC-RAS hydraulic-hydrodynamic model was forced by the flood hydrographs and map the inundated areas. A flash flood event occurred on 15 November 2017 in Mandra, Attica, Greece, causing 24 fatalities, and damages was selected as case study. The calibration of models was performed exploiting historical flood records and previous studies. Human interventions such as hydraulic works and the urban areas were included in the hydraulic modelling geometry domain. The representation of the resistance caused by buildings was based on Unmanned Aerial System (UAS) data while the local elevation rise method was used in the urban-flood simulation. The flood extent results were assessed using the Critical Success Index (CSI), and CSI penalize. Integrating sea-state affected the forecast of precipitation and discharge peaks, causing up to +24% and from −8% to +36% differences, respectively, improving inundation forecast by 4.5% and flooding additional approximately 70 building blocks. The precipitation forcing time step was also highlighted as significant factor in such a small-scale flash flood. The integrated multidisciplinary methodological approach could be adopted in operational forecasting for civil protection applications facilitating the protection of socio-economic activities and human lives during similar future events. 相似文献
35.
Petros Koutsovitis 《Mineralogy and Petrology》2012,104(3-4):249-265
East Othris area consists of scattered ophiolitic units, as well as ophiolitic mélange occurrences, which encompass gabbroic rocks. These rocks have been affected by low-grade ocean floor metamorphism (T?<?350°C and P?<?8?kbar). Based on their petrography, mineral chemistry and geochemistry gabbroic rocks have been distinguished into gabbros and diorites, with the latter being divided into two groups. Gabbros seem to have been formed from moderate to high partial melting degrees (~8–25%) of a highly depleted mantle source, while group (1) diorites have been differentiated after variable fractionation processes (up to 30%). Group (2) diorites seem to have been derived from low partial melting degrees (~3%) of a fertile or moderately depleted mantle source and with extensive fractionation processes (~50%). Geochemical results suggest that partial melting processes occurred at relatively shallow depths, in the plagioclase-spinel stability field, while amphibole chemistry data indicate shallow level crystallization. Chondrite and PM-normalized patterns, Th/Yb, and Nb/Th ratios as well as mineral chemistry analyses show that gabbros and group (1) diorites (with relatively low PM-normalized Nb and Ta values and negative Ti anomalies) suggest subduction processes, while group (2) diorites are MORB or BAB related. Some gabbros have been characterised as high-Mg, being compositionally similar to picrites or boninites. Variability in extent of partial melting of the mantle source and the different geotectonic environment affinities are consistent with a supra-subduction zone (SSZ) origin of the east Othris ophiolites. The fact that IAT related rocks are more abundant in east rather than in west Othris may possibly be explained by a slab rollback model retreating to the east within the Pindos oceanic basin. 相似文献
36.
37.
Papadopoulou Penelope Iliopoulos George Tsoni Maria Koukouvelas Ioannis Groumpos Petros 《Mathematical Geosciences》2021,53(8):1841-1860
Mathematical Geosciences - This work aims to test and introduce a newly developed methodological approach for palaeoenvironmental reconstructions using advanced intelligent controls, namely fuzzy... 相似文献
38.
The combination of accretion disks and supersonic jets is used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei. However, existing theories on the physical processes by which these structures transfer angular momentum and energy from disks to jets through viscous or magnetic torques are still relatively approximate. Global stationary solutions do not permit understanding the formation and stability of these structures; and global numerical simulations that include both the disk and jet physics are often limited to relatively short time scales and astrophysically out-of-range values of viscosity and resistivity parameters that are instead crucial to defining the coupling of the inflow/outflow dynamics. Along these lines we discuss self-consistent time-dependent simulations of the launching of supersonic jets by magnetized accretion disks, using high resolution numerical techniques. We shall concentrate on the effects of the disk physical parameters, and discuss under which conditions steady state solutions of the type proposed in the self-similar models of Blandford and Payne can be reached and maintained in a self-consistent nonlinear stationary state. 相似文献
39.
Stabiliity is applied to characterize type of motion in which the moving body is confined to certain limited regions and in this sense we may say that the motion of the body in question is stable. This method has been used in the past chiefly in connection with the classical restricted problem of three bodies.In this paper we consider a dynamical system defined by the Lagrangian
|
相似文献
40.
In its current status, medical imaging involves a wide range of imaging modalities and is faced with a range of interesting research questions, while trying to automatically convert the huge floods of image data to useful information. The major characteristic of the developed techniques is the exploitation of visual similarities or differences; that is basically qualitative treatment of the information inherent in the images. This proves to be a major shortcoming, leading to erroneous or unreliable results in many cases. To this end, technology transfer from the part of photogrammetry can be proven very beneficial. Such a contribution can be geared by the fact that photogrammetry has developed efficient tools for accounting for imaging formation geometry. These tools, appropriately tuned for medical applications, can accelerate the technology transfer across the involved disciplines. Understanding the possible photogrammetric contributions by the medical imaging experts, and realizing the medical problems in photogrammetric terms by the photogrammetrists, remains a major barrier to this transfer. The intended scope of this paper is to provide a foundation for exchange of ideas and provoke photogrammetric research interest in these issues. 相似文献
|