Anisotropic Mesh Adaptivity and Control Volume Finite Element Methods for Numerical Simulation of Multiphase Flow in Porous Media   总被引：1，自引：1，他引：0  

Peyman Mostaghimi  James R. Percival  Dimitrios Pavlidis  Richard J. Ferrier  Jefferson L. M. A. Gomes  Gerard J. Gorman  Matthew D. Jackson  Stephen J. Neethling  Christopher C. Pain 《Mathematical Geosciences》2015,47(4):417-440

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Estimation of satellite position,clock and phase bias corrections     

Patrick Henkel  Dimitrios Psychas  Christoph Günther  Urs Hugentobler 《Journal of Geodesy》2018,92(10):1199-1217

Precise point positioning with integer ambiguity resolution requires precise knowledge of satellite position, clock and phase bias corrections. In this paper, a method for the estimation of these parameters with a global network of reference stations is presented. The method processes uncombined and undifferenced measurements of an arbitrary number of frequencies such that the obtained satellite position, clock and bias corrections can be used for any type of differenced and/or combined measurements. We perform a clustering of reference stations. The clustering enables a common satellite visibility within each cluster and an efficient fixing of the double difference ambiguities within each cluster. Additionally, the double difference ambiguities between the reference stations of different clusters are fixed. We use an integer decorrelation for ambiguity fixing in dense global networks. The performance of the proposed method is analysed with both simulated Galileo measurements on E1 and E5a and real GPS measurements of the IGS network. We defined 16 clusters and obtained satellite position, clock and phase bias corrections with a precision of better than 2 cm.  相似文献   

Correction to: Estimation of satellite position,clock and phase bias corrections     

Patrick Henkel  Dimitrios Psychas  Christoph Günther  Urs Hugentobler 《Journal of Geodesy》2018,92(10):1219-1221

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Extraction and predictability of coherent intraseasonal signals in infrared brightness temperature data     

Eniko Székely  Dimitrios Giannakis  Andrew J. Majda 《Climate Dynamics》2016,46(5-6):1473-1502

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Solution of the linear diffusion equation for modelling erosion processes with a time varying diffusion coefficient     

Georgios Aim. Skianis  Dimitrios Vaiopoulos  Niki Evelpidou 《地球表面变化过程与地形》2008,33(10):1491-1501

In the present paper the differential equation of the temporal development of a landform (mountain) with a time dependent diffusion coefficient is solved. It is shown that the shape and dimensions of the landform at time t are independent of the specific variation of the diffusion coefficient with time; they only depend on the mean value of the diffusion coefficient in the time interval where the erosion process takes place. Studying the behaviour of the solution of the differential equation in the wave number domain, it is concluded that Fourier analysis may help in estimating, in quantitative terms, the initial dimensions, the age or, alternatively, the value of the diffusion coefficient of the landform. The theoretical predictions are tested on a hill of the southern part of the Ural mountainous region, in order to show how the results of the mathematical analysis can be used in describing, in quantitative terms, the morphological development of landforms due to erosion processes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Seismic intensity measures for above‐ground liquid storage tanks          下载免费PDF全文

Konstantinos Bakalis  Mohsen Kohrangi  Dimitrios Vamvatsikos 《地震工程与结构动力学》2018,47(9):1844-1863

A series of scalar and vector intensity measures is examined to determine their suitability within the seismic risk assessment of liquid storage tanks. Using a surrogate modelling approach on a squat tank that is examined under both anchored and unanchored support conditions, incremental dynamic analysis is adopted to generate the distributions of response parameters conditioned on each of the candidate intensity measures. Efficiency and sufficiency metrics are used in order to perform the intensity measure evaluation for individual failure modes, while a comparison in terms of mean annual frequency of exceedance is performed with respect to a damage state that is mutually governed by the impulsive and convective modes of the tank. The results reveal combinations of spectral acceleration ordinates as adequate predictors, among which the average spectral acceleration is singled out as the optimal solution. The sole exception is found for the sloshing‐controlled modes of failure, where mainly the convective period spectral acceleration is deemed adequate to represent the associated response due to their underlying linear relationship. A computationally efficient method in terms of site hazard analysis is finally proposed to serve in place of the vector‐valued intensity measures, providing a good match for the unanchored tank considered and a more conservative one for the corresponding anchored system.  相似文献   

Earthquake precursory signatures in electromagnetic radiation measurements in terms of day-to-day fractal spectral exponent variation: analysis of the eastern Aegean 13/04/2017–20/07/2017 seismic activity     

Demetrios Cantzos  Dimitrios Nikolopoulos  Ermioni Petraki  Panayotis Yannakopoulos  Constantinos Nomicos 《Journal of Seismology》2018,22(6):1499-1513

The recent seismic activity in the eastern Aegean Sea, foregrounded by two major (M_L?=?6.1 and M_L?=?6.2) earthquakes occurring near Lesvos and Kos islands, respectively, is investigated in this work. Electromagnetic radiation measurements across different frequency bands and antenna orientations from a monitoring station in Agia Paraskevi, Lesvos Island, are analysed in order to reveal earthquake precursory signatures hidden in the electromagnetic data sequence. A straightforward, data-driven approach is employed in which day-to-day variations of the fractal characteristics of the measurements are adaptively monitored via a fractal spectral exponent similarity measure. The evolution of the fractal day-to-day variation in a 99-day period, which includes the two major earthquakes, shows a sustained, sudden increase lasting 1 to 4 days before every earthquake cluster of M_L?=?4.0 and above. Most importantly, this day-to-day variation subsides shortly after and remains relatively low during the absence of earthquakes, thus alleviating the emergence of false alarms.  相似文献   

Fiber-based hysteretic model for simulating strength and stiffness deterioration of steel hollow structural section columns under cyclic loading     

Yusuke Suzuki  Dimitrios G. Lignos 《地震工程与结构动力学》2020,49(15):1702-1720

An efficient component model has been developed that captures strength and stiffness deterioration of steel hollow structural section (HSS) columns. The proposed model consists of two fiber-based segments at a member's ends along with an elastic segment in between. The fibers exhibit nonlinear uniaxial stress–strain behavior, which is explicitly defined by uniaxial monotonic tensile and cyclic round coupon tests. The postbuckling behavior of an HSS column is traced through a proposed uniaxial effective stress–strain constitutive formulation, which includes a softening branch in compression and an energy-based deterioration rule to trace the influence of cyclic deterioration in the inelastic cyclic straining. These may be inferred by uniaxial stub-column tests. The component model captures the coupling between the column axial force and flexural demands. Consistent model parameters for a number of steel materials used in the steel construction in North America and Japan are proposed along with the associated model calibration process. The efficiency of the proposed model in predicting the hysteretic behavior of HSS columns is demonstrated by comparisons with physical steel column tests subjected to various loading histories, including representative ones of ratcheting prior to earthquake-induced collapse. The proposed model is implemented in an open-source finite element software for nonlinear response history analysis of frame structures. The effectiveness of the proposed model in simulating dynamic instability of steel frame buildings is demonstrated through nonlinear response simulations of a four-story steel frame building, which was tested at full-scale through collapse. Limitations as well as suggestions for future work are discussed.  相似文献   

Dynamics of a sliding-rocking block considering impact with an adjacent wall     

Yu Bao  Dimitrios Konstantinidis 《地震工程与结构动力学》2020,49(5):498-523

A freestanding rigid block subjected to base excitation can exhibit complicated motion described by five response modes: rest, pure rocking, pure sliding, combined sliding-rocking, and free flight. Previous studies on the dynamics of a rocking block have assumed that the block does not interact with neighboring objects. However, there are many applications in which the block may start or come in contact with an adjacent boundary during its motion, for example, a bookcase or cabinet colliding with a partition wall in an earthquake. This paper investigates the dynamics of a sliding-rocking block considering impact with an adjacent wall. A model is developed in which the base and wall are assumed rigid, and impact is treated using the classical impulse and momentum principle. The model is verified by comparing its predictions in numerical simulations against those of an existing general-purpose rigid-body model in which impact is treated using a viscoelastic impact model. The developed model is used to investigate the effects of different parameters on the stability of a block subjected to analytical pulse excitations. It is found that wall placement (left or right) has a dominant effect on the shape of the overturning acceleration spectra for pulse excitations. In general, decreasing the gap distance, base friction coefficient, and wall coefficient of restitution enhance the stability of the block. Similar observations are made when evaluating the overturning probability of a block using earthquake floor motions.  相似文献   

Conditional spectrum‐based ground motion record selection using average spectral acceleration          下载免费PDF全文

Mohsen Kohrangi  Paolo Bazzurro  Dimitrios Vamvatsikos  Andrea Spillatura 《地震工程与结构动力学》2017,46(10):1667-1685

The use of a seismic intensity measure (IM) is paramount in decoupling seismic hazard and structural response estimation when assessing the performance of structures. For this to be valid, the IM needs to be sufficient;that is, the engineering demand parameter (EDP) response should be independent of other ground motion characteristics when conditioned on the IM. Whenever non‐trivial dependence is found, such as in the case of the IM being the first‐mode spectral acceleration, ground motion selection must be employed to generate sets of ground motion records that are consistent vis‐à‐vis the hazard conditioned on the IM. Conditional spectrum record selection is such a method for choosing records that are consistent with the site‐dependent spectral shape conditioned on the first‐mode spectral acceleration. Based on a single structural period, however the result may be suboptimal, or insufficient, for EDPs influenced by different period values, for example, peak interstory drifts or peak floor accelerations at different floors, potentially requiring different record suites for each. Recently, the log‐average spectral acceleration over a period range, AvgSA, has emerged as an improved scalar IM for building response estimation whose hazard can be evaluated using existing ground motion prediction equations. Herein, we present a recasting of conditional spectrum record selection that is based on AvgSA over a period range as the conditioning IM. This procedure ensures increased efficiency and sufficiency in simultaneously estimating multiple EDPs by means of a single IM. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献