Nonlinear dynamics of two degree of freedom systems with linear and nonlinear stiffnesses     

Bayat Mahmoud  I.Pakar 《地震工程与工程振动(英文版)》2013,12(3):411-420

In this study,a new analytical approach is developed to analyze the free nonlinear vibration of conservative two-degree-of-freedom(TDOF) systems.The mathematical models of these systems are governed by second–order nonlinear partial differential equations.Nonlinear differential equations were transferred into a single equation by using some intermediate variables.The single nonlinear differential equations are solved by using the first order of the Hamiltonian approach(HA).Different parameters,which have a significant impact on the response of the systems,are considered and discussed.Some comparisons are presented to verify the results between the Hamiltonian approach and the exact solution.The maximum relative error is less than 2.2124 % for large amplitudes of vibration.It has been established that the first iteration of the Hamiltonian approach achieves very accurate results,does not require any small perturbations,and can be used for a wide range of nonlinear problems.  相似文献   

Automatic extraction of road intersection points from USGS historical map series using deep convolutional neural networks     

Mahmoud Saeedimoghaddam 《International journal of geographical information science》2020,34(5):947-968

ABSTRACT

Road intersection data have been used across a range of geospatial analyses. However, many datasets dating from before the advent of GIS are only available as historical printed maps. To be analyzed by GIS software, they need to be scanned and transformed into a usable (vector-based) format. Because the number of scanned historical maps is voluminous, automated methods of digitization and transformation are needed. Frequently, these processes are based on computer vision algorithms. However, the key challenges to this are (1) the low conversion accuracy for low quality and visually complex maps, and (2) the selection of optimal parameters. In this paper, we used a region-based deep convolutional neural network-based framework (RCNN) for object detection, in order to automatically identify road intersections in historical maps of several cities in the United States of America. We found that the RCNN approach is more accurate than traditional computer vision algorithms for double-line cartographic representation of the roads, though its accuracy does not surpass all traditional methods used for single-line symbols. The results suggest that the number of errors in the outputs is sensitive to complexity and blurriness of the maps, and to the number of distinct red-green-blue (RGB) combinations within them.  相似文献   

Hydroelastic vibration and buckling of rectangular Mindlin plates on Pasternak foundations under linearly varying in-plane loads     

Sh. Hosseini-Hashemi  Mahmoud Karimi  D.T. Hossein Rokni 《Soil Dynamics and Earthquake Engineering》2010

Hydroelastic vibration and buckling analysis of horizontal rectangular plates resting on Pasternak foundation and subjected to linearly varying in-plane loads is investigated for different boundary conditions. Fluid is assumed to be inviscid and incompressible. To analyze the interaction of the Mindlin plate with the elastic foundation and fluid system, three displacement components of the plate are expressed in the Ritz method by adopting a set of static Timoshenko beam functions satisfying geometric boundary conditions. Convergence study is first carried out to confirm the stability of the present method. Then, a few comparisons are made for limited cases between present results and the available data in the literature. Finally, parametric study is conducted to highlight the effects of loading factors, fluid levels, foundation stiffness parameters, aspect ratios, thickness to width ratios and different boundary conditions on the critical buckling loads and wet natural frequencies of rectangular plates.  相似文献   

Imaging the Mariánské Lázně Fault (Czech Republic) by 3-D ground-penetrating radar and electric resistivity tomography     

Tomá? Fischer  Petra ?těpan?íková  Magda Karousová  Petr Tábo?ík  Christina Flechsig  Mahmoud Gaballah 《Studia Geophysica et Geodaetica》2012,56(4):1019-1036

Geodynamic activity in the area of West Bohemia is typified by the occurrence of earthquake swarms, Quaternary volcanism and high flux of mantle-derived CO₂. The highest swarm activity occurs beneath the eastern edge of the Cheb basin, which is delineated by the NW-SE trending morphologically pronounced Mariánské Lázn?? Fault (MLF) controlling the formation of the basin. The previous trenching survey across the MLF zone has identified several fault strands with possible Quaternary activity. In this paper we present the results of the geophysical survey focused to trace the faults signatures in geophysical sections and to build an image of near surface tectonics. The method of electric resistivity tomography (ERT) along two profiles parallel to the trench identified a strong resistivity contrast between the bodies of sandy gravels in the middle and conductive clayey sands to the west and weathered crystalline basement to the east. The 2-D ground penetration radar (GPR) sections show direct correlation of reflections with lithological boundaries identified in the trench. As expected, the GPR signal amplitudes increase with the resistivities found in the ERT sections. Two of the four faults identified in the trench are indicated in the resistivity and GPR sections. A 3-D GPR measurement has identified a spot of high amplitudes elongated parallel to the MLF trend, which coincides with the high resistivity body. To improve the signal-to-noise ratio of the time slices we stacked the GPR time slices within vertically homogeneous blocks. This provided a contrast image of the sand-gravel body including its boundaries in three dimensions. The detailed analysis of the 3-D GPR cube revealed additional fault that limits the highly reflective sands and appears to be offset by another younger fault. Our results suggest a complex fault pattern in the studied area, which deserves a further study.  相似文献   

Environmental and Health Impacts of Successive Mineral Fertilization in Egypt     

Ahmed A. Abdelhafez  Hassan H. Abbas  Rafat S. Abd‐El‐Aal  Nabil F. Kandil  Jianhua Li  Wahballah Mahmoud 《洁净——土壤、空气、水》2012,40(4):356-363

Excessive amounts of mineral fertilizers are unnecessarily applied to agricultural soils in Egypt to increase crop yield. The current study aims at assessing the impacts of fertilization with different mineral fertilizers for different cultivation periods on the accumulation of heavy metals in soils and plants grown thereon. In addition, human risks resulted due to the exposure to these metal ions through ingestion, and dermal routes were evaluated. Soil and plant samples were collected from several locations in El‐Behira Governorate, Egypt and their heavy metal contents were measured. The result indicated that there is a continuous accumulation of heavy metals in the soils and the plants grown thereon. Calculation of the hazard index (HI) revealed that humans, especially children, have a potential health risk for both Pb and Cd, which have levels greater than the safe level (1). Finally, the obtained results showed that the continuous application of mineral fertilizers containing high levels of heavy metals pose a potential health threat.  相似文献   

Linking of adjacent three-storey buildings for mitigation of structural pounding during earthquakes     

Robert Jankowski  Sayed Mahmoud 《Bulletin of Earthquake Engineering》2016,14(11):3075-3097

The reports after major earthquakes indicate that the earthquake-induced pounding between insufficiently separated buildings may lead to significant damage or even total collapse of structures. An intensive study has recently been carried out on mitigation of pounding hazards so as to minimize the structural damages or prevent collisions at all. The aim of this paper is to investigate the effectiveness of the method when two adjacent three-storey buildings with different (substantially different) dynamic properties are connected at each storey level by link elements (springs, dashpots or viscoelastic elements). The results of the study indicate that connecting the structures by additional link elements can be very beneficial for the lighter and more flexible building. The largest decrease in the response of the structure has been obtained for links with large stiffness or damping values, which stands for the case when two buildings are fully connected and vibrate in-phase. Moreover, by comparing the effectiveness of different types of link elements, it has been confirmed that the use of viscoelastic elements reduces the peak displacement of the structure at lower stiffness and damping values comparing to the case when spring and dashpot elements are applied alone. On the other hand, the results of the study demonstrate that applying the additional link elements does not really change the response of the heavier and stiffer building. The final conclusion of the study indicates that linking two buildings allows us to reduce the in-between gap size substantially while structural pounding can be still prevented.  相似文献   

Analytical Method Development for the Screening and Determination of Dioxins in Clay Matrices          下载免费PDF全文

Mahmoud A. Alawi  Ahmad A. Najjar  Hani N. Khoury 《洁净——土壤、空气、水》2014,42(7):979-985

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