Origin and characteristics of yardangs in the Um Al-Rimam depressions (N Kuwait)   总被引：3，自引：0，他引：3  

Ali. M. Al-Dousari  Maraheb Al-Elaj  Eqbal Al-Enezi  Abdulaziz Al-Shareeda 《Geomorphology》2009,104(3-4):93-104

Although Arabia hosts one of the largest deserts in the world, studies regarding aeolian erosional features in general and yardangs in particular are rare. The principal aim of this study is to delineate and investigate the various forms of yardangs in the Um Al-Rimam depressions in the northern part of Kuwait. The study area consists of two main depressions connected by neck area made up of continental sediments. Both depressions are surrounded by a dissected escarpment and their floors host muddy playas. On lithological bases, three main types of yardang have been identified: 7 yardangs are sculptured in sandstones of Lower Fars Formation (Lower to Middle Miocene), 23 are carved in calcretic rocks of Ghar Formation (Oligocene to Lower Miocene), and 11 yardangs are developed in Quaternary sediments. Their mean orientation NW (297°) coincides with the prevailing direction of the strong local northwesterly wind called the shamal. The average length/width ratio is 1.5:1. The wide geographic distribution of yardangs around the margins of the northern depression is due to sand blasting. This is explained by the annual sand accumulation measured in the study area where the northern depression shows 143 times higher accumulation than the southern depression, the neck area and the platform above the depressions. Also, the field measurements for annual erosional rates show that the sides of the yardangs are more affected by erosion compared to their middle parts. Remarkably slight mineralogical variations were detected within the surface sediments of Um Al-Rimam depressions and the Quaternary muddy yardangs which indicate a common origin. The age of yardangs is unknown but annual erosional rates on a small Quaternary muddy yardang suggest that they range in age between 44 and 1500 years depending on yardang size. It is believed, as indicated from field observation and interpretation of aerial photos, that the majority of yardangs are pre-existing bedrock forms. These forms were developed by paleo-surface hydrological processes which were modified by wind action in latter phase.  相似文献   

The effect of foundation embedment on inelastic response of structures     

Mojtaba Mahsuli  M. Ali Ghannad 《地震工程与结构动力学》2009,38(4):423-437

In this research, a parametric study is carried out on the effect of soil–structure interaction on the ductility and strength demand of buildings with embedded foundation. Both kinematic interaction (KI) and inertial interaction effects are considered. The sub‐structure method is used in which the structure is modeled by a simplified single degree of freedom system with idealized bilinear behavior. Besides, the soil sub‐structure is considered as a homogeneous half‐space and is modeled by a discrete model based on the concept of cone models. The foundation is modeled as a rigid cylinder embedded in the soil with different embedment ratios. The soil–structure system is then analyzed subjected to a suit of 24 selected accelerograms recorded on alluvium deposits. An extensive parametric study is performed for a wide range of the introduced non‐dimensional key parameters, which control the problem. It is concluded that foundation embedment may increase the structural demands for slender buildings especially for the case of relatively soft soils. However, the increase in ductility demands may not be significant for shallow foundations with embedment depth to radius of foundation ratios up to one. Comparing the results with and without inclusion of KI reveals that the rocking input motion due to KI plays the main role in this phenomenon. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Three-dimensional semi-analytical solution to groundwater flow in confined and unconfined wedge-shaped aquifers     

Mohammad Mahdi Sedghi  Nozar Samani  Brent Sleep 《Advances in water resources》2009

The Laplace domain solutions have been obtained for three-dimensional groundwater flow to a well in confined and unconfined wedge-shaped aquifers. The solutions take into account partial penetration effects, instantaneous drainage or delayed yield, vertical anisotropy and the water table boundary condition. As a basis, the Laplace domain solutions for drawdown created by a point source in uniform, anisotropic confined and unconfined wedge-shaped aquifers are first derived. Then, by the principle of superposition the point source solutions are extended to the cases of partially and fully penetrating wells. Unlike the previous solution for the confined aquifer that contains improper integrals arising from the Hankel transform [Yeh HD, Chang YC. New analytical solutions for groundwater flow in wedge-shaped aquifers with various topographic boundary conditions. Adv Water Resour 2006;26:471–80], numerical evaluation of our solution is relatively easy using well known numerical Laplace inversion methods. The effects of wedge angle, pumping well location and observation point location on drawdown and the effects of partial penetration, screen location and delay index on the wedge boundary hydraulic gradient in unconfined aquifers have also been investigated. The results are presented in the form of dimensionless drawdown-time and boundary gradient-time type curves. The curves are useful for parameter identification, calculation of stream depletion rates and the assessment of water budgets in river basins.  相似文献   

Route Matching in Sketch and Metric Maps     

Zare Zardiny  Ali  Hakimpour  Farshad 《Journal of Geographical Systems》2021,23(3):381-405

Journal of Geographical Systems - Despite all distortions and incompleteness present in Sketch maps, they can be used for different purposes such as collecting and searching spatial data and...  相似文献   

A two-step wavelet-based regularization for linear inversion of geophysical data     

Ali Gholami  Hamid Reza Siahkoohi 《Geophysical Prospecting》2009,57(5):847-862

Regularization methods are used to recover a unique and stable solution in ill-posed geophysical inverse problems. Due to the connection of homogeneous operators that arise in many geophysical inverse problems to the Fourier basis, for these operators classical regularization methods possess some limitations that one may try to circumvent by wavelet techniques.
In this paper, we introduce a two-step wavelet-based regularization method that combines classical regularization methods with wavelet transform to solve ill-posed linear inverse problems in geophysics. The power of the two-step wavelet-based regularization for linear inversion is twofold. First, regularization parameter choice is straightforward; it is obtained from a priori estimate of data variance. Second, in two-step wavelet-based regularization the basis can simultaneously diagonalize both the operator and the prior information about the model to be recovered. The latter is performed by wavelet-vaguelette decomposition using orthogonal symmetric fractional B-spline wavelets.
In the two-step wavelet-based regularization method, at the first step where fully classical tools are used, data is inverted for the Moore-Penrose solution of the problem, which is subsequently used as a preliminary input model for the second step. Also in this step, a model-independent estimate of data variance is made using nonparametric estimation and L-curve analysis. At the second step, wavelet-based regularization is used to partially recover the smoothness properties of the exact model from the oscillatory preliminary model.
We illustrated the efficiency of the method by applying on a synthetic vertical seismic profiling data. The results indicate that a simple non-linear operation of weighting and thresholding of wavelet coefficients can consistently outperform classical linear inverse methods.  相似文献   

Impact of season and road on stream crossings and river water quality in Darabkola,hyrcanian forest     

Mananeh Akbarimehr  Seyed Ataollah Hosseini  Fatemeh Shariati  Seyed Mohammad Hodjati 《Water Resources》2016,43(2):369-376

Nutrients are important building blocks for healthy aquatic ecosystems and are generally nontoxic; but they can change with alteration in environmental parameters. The main objective of this study was to consider the seasonal variability of NO ₃ ^– , PO ₄ ^3– and total suspended solids (TSS) concentrations in water. The study sites, stream crossings (L30, L15) and river (R), are located in the hyrcanian forests, district 1 of Darabkola forest. The sampling was conducted in winter and spring. Water samples were taken into plastic bottles, labeled, and carried out to the laboratory for NO ₃ ^– , PO ₄ ^3– and TSS analysis. T-test results showed that there was a seasonal change in nutrient concentrations (p < 0.05) except for NO ₃ ^– concentration at L30. Also, there was no significant seasonal change in TSS concentrations at all stations. Pearson correlation analysis did not reveal the same trend. Further analysis showed that the effect of road age on water quality parameters was statistically significant for PO ₄ ^3– in spring and winter. Atmospheric precipitation plays vital role in nutrient loss and increasing concentration of suspended sediment. To prevent soil erosion from activities and discharge of wastes in the vicinity of river and stream an effective management should be planned and enforced.  相似文献   

Quantification of seismic potential failure modes in concrete dams          下载免费PDF全文

Mohammad Amin Hariri‐Ardebili  Victor. E. Saouma  Keith A. Porter 《地震工程与结构动力学》2016,45(6):979-997

A comprehensive framework for potential failure modes (PFM) identification and quantification of concrete dams subjected to seismic excitation is presented. A quantifiable indicator of PFM is presented in the context of both linear and nonlinear analyses. As an illustrative example, a thin arch dam subjected to a set of ground motions at different seismic intensity levels is investigated and corresponding PFM quantified. An outcome of this analysis is the probabilistic‐based correlation between linear and nonlinear analyses and identification of the optimal intensity measure parameter. This study, is an adaptation and extension of well‐accepted procedures defined by the performance‐based earthquake engineering paradigm in buildings. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Systematic development of a new hysteretic damper based on torsional yielding: part I—design and development          下载免费PDF全文

Ali Salem Milani  Murat Dicleli 《地震工程与结构动力学》2016,45(6):845-867

Analytical and experimental studies into the behavior of a new hysteretic damper, designed for seismic protection of structures is presented in two papers. Although the subject matter of the papers is a specific system, they are also intended as an illustration of practical application of diverse engineering tools in systematic development of an anti‐seismic product. The Multi‐directional Torsional Hysteretic Damper (MTHD) is a recently patented invention in which a symmetrical arrangement of identical cylindrical steel energy dissipaters is configured to yield in torsion while the structure experiences planar movements due to earthquake shakings. The device has gone through many stages of design refinement, prototype verification tests and development of design guidelines and computer codes to facilitate its implementation in practice. The first of this two‐part paper summarizes the development stages of the new system, conceptual and analytical. The experimental phase of the research is the focus of the accompanying paper. The new device has certain desirable properties. Notably, it is characterized by a variable and controllable‐via‐design or adaptive post‐elastic stiffness. This feature gives the isolated structure the capability to evade the dominant period of the ground motion leading to reduced displacements while having force levels comparable to regular bilinear isolation systems. The device has already been applied to four major bridges. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Systematic development of a new hysteretic damper based on torsional yielding: part II—experimental phase          下载免费PDF全文

Ali Salem Milani  Murat Dicleli 《地震工程与结构动力学》2016,45(5):779-796

This paper reports on experimental studies carried out on a 200 kN, 120 mm‐capacity prototype of the newly developed multidirectional torsional hysteretic damper for seismic protection of structures. The main goal of the experiments is to test the validity of the theory developed in a companion paper and to evaluate the low‐cycle fatigue performance of the energy dissipaters of the damper. Because the design and configuration of the damper allow easy replacement of the energy dissipaters, four sets of energy dissipaters were produced out of S355J2 + N, C45 (two sets), and 42CrMo4 + QT steel grades. Force–displacement response of the multidirectional torsional hysteretic damper is studied through fully reversed cyclic quasi‐static displacement‐controlled tests that were carried out in compliance with EN 15129. Following the verification tests, with the aim of studying fatigue and fracture behavior of the cylindrical energy dissipaters of the device, certain numbers of them were subjected to further cyclic tests up to failure, and observations on their fatigue/fracture behavior are reported. The experimental verification test results proved the validity of the developed theory and component design assumptions presented in a companion paper. Furthermore, the energy dissipaters exhibited excellent torsional low‐cycle fatigue performance with number of cycles to failure reaching 118 at a maximum shear strain of 8% for S355J2 + N steel grade. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Multivariate approach for chlorophyll-a and suspended matter retrievals in Case II type waters using hyperspectral data     

Khalid A. Ali  Joseph D. Ortiz 《水文科学杂志》2013,58(1):200-213

Abstract

Remote sensing has become promising in providing temporal and spatial information on biogeodynamics in large and open freshwater bodies. In optically complex environments, such as in the Western Basin of Lake Erie (WBLE), the water contains multiple biogeochemical constituents or colour producing agents (CPAs), such as phytoplankton, suspended matter and dissolved organic carbon; identifying and analysing such in-water constituents is crucial for understanding and assessing many biogeochemical processes. For example, concentrations of chlorophyll-a and total suspended matter can be used as proxies to assess phytoplankton dynamics and particulate loading. However, quantitative estimation of their concentrations from satellite observations is complicated when working with mixed spectral signatures. Hyperspectral remote sensing is fast emerging as a key technology for advanced and improved understanding of optically complex waters. This study estimates concentrations of chlorophyll-a and total suspended matter (TSM) in the WBLE by applying the partial least squares (PLS) method to a full range (400–900 nm) of continuous narrow spectral bands. The PLS method models the covariance between hyperspectral bands and CPAs, and identifies the optimal bands that characterize most of the variance in the CPAs. This method avoids the curse of dimensionality and the effects of multi-collinearity, a challenge that is associated with new-generation hyperspectral satellite sensors. Validation parameters for the PLS-based models produced R² of 0.84 for chlorophyll-a (RMSE = 1.18 μg/L), and R² of 0.90 for TSM (RMSE = 1.26 mg/L), illustrating the potential of the PLS method for isolating and extracting absorption features characterizing the various CPAs in optically complex Case II type waters.