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61.
The dynamic characteristics of a circular cylindrical shell in contact with a liquid are theoretically studied. The cantilevered cylindrical shell with open ends is partially submerged in a liquid which is unbounded in the radial direction, but bounded by a rigid and flat bottom. Since the liquid is assumed to be incompressible and inviscid, the liquid motion can be described as the velocity potentials written in terms of the appropriate Bessel functions for both the inner and the outer liquid regions. The compatibility of the dynamic displacement along the contacting surfaces between the shell and liquid leads the resulting equations, satisfying both the shell and liquid motions, which are solved by using the collocation method. Finally, the Rayleigh–Ritz method is applied to extract the wet natural frequencies and the mode shapes of the liquid-coupled system. The validity of the theoretical method is established with the aid of a commercial finite element computer code. In order to evaluate the dynamic characteristics of the liquid-coupled system, the effects of the submerged depth and the axial gap between the bottom end of the shell and the bottom surface of the liquid are demonstrated. 相似文献
62.
Support system suggestion based on back-analysis results case study: Babolak water conveyance tunnel
Ehsan Dadashi Kaveh Ahangari Ali Noorzad Alireza Arab 《Arabian Journal of Geosciences》2012,5(6):1297-1306
Determining in-situ soil or rock geotechnical properties is a difficult task for a design engineer. Back analysis is a helpful technique for evaluating soil property by considering and measuring the convergence of an underground opening. Back analysis was performed by matching numerical modeling results with the measured tunnel convergence. The main purpose of this study was to determine optimum rock mass properties using back analysis in order to suggest the best and most economical support system. Accordingly, the difference between measured and calculated convergence values was minimized by using an error function (objective function). In this paper, through the parameters obtained from back analysis, a support system based on a set consisting of shotcrete, wire mesh, and lattice girder was suggested for the Babolak water conveyance tunnel in Mazandaran, Iran. Therefore, the suggested design was based on decreasing shotcrete thickness from 25 to 20?cm and eliminating of rock bolts. 相似文献
63.
Ship board testing of a deoxygenation ballast water treatment 总被引：2，自引：1，他引：1
McCollin T Quilez-Badia G Josefsen KD Gill ME Mesbahi E Frid CL 《Marine pollution bulletin》2007,54(8):1170-1178
A ship board trial of a deoxygenation method for treating ballast water was carried out during a voyage from Southampton (United Kingdom) to Manzanillo (Panama). A nutrient solution added to two ballast tanks encouraged bacterial growth, resulting in a gradual change to an anoxic environment. Samples were taken from two treated tanks and two untreated tanks to assess changes in the abundance and viability of zooplankton, phytoplankton and bacteria. The work was carried out before the International Maritime Organization (IMO) standard was agreed so only a broad indication of whether the results achieved the standard was given. For the zooplankton, the standard would have been achieved within 5 or 7 days but the phytoplankton results were inconclusive. The biological efficacy was the result of the combination of several factors, including the treatment, pump damage and an increase in the water temperature during the voyage. 相似文献
64.
A precise value of the matrix-fracture transfer shape factor is essential for modeling fluid flow in fractured porous media by a dual-porosity approach. The slightly compressible fluid shape factor has been widely investigated in the literature. In a recent study, we have developed a transfer function for flow of a compressible fluid using a constant fracture pressure boundary condition [Ranjbar E, Hassanzadeh H, Matrix-fracture transfer shape factor for modeling flow of a compressible fluid in dual-porosity media. Adv Water Res 2011;34(5):627-39. doi:10.1016/j.advwatres.2011.02.012]. However, for a compressible fluid, the consequence of a pressure depletion boundary condition on the shape factor has not been investigated in the previous studies. The main purpose of this paper is, therefore, to investigate the effect of the fracture pressure depletion regime on the shape factor for single-phase flow of a compressible fluid. In the current study, a model for evaluation of the shape factor is derived using solutions of a nonlinear diffusivity equation subject to different pressure depletion regimes. A combination of the heat integral method, the method of moments and Duhamel’s theorem is used to solve this nonlinear equation. The developed solution is validated by fine-grid numerical simulations. The presented model can recover the shape factor of slightly compressible fluids reported in the literature. This study demonstrates that in the case of a single-phase flow of compressible fluid, the shape factor is a function of the imposed boundary condition in the fracture and its variability with time. It is shown that such dependence can be described by an exponentially declining fracture pressure with different decline exponents. These findings improve our understanding of fluid flow in fractured porous media. 相似文献
65.
Negin Kananizadeh Taghi Ebadi Seyed Alireza Khoshniat Seyed Ehsan Mousavirizi 《洁净——土壤、空气、水》2011,39(7):605-611
This study evaluates the effect of nanoclay on permeability, swelling, compressive strength, and cation exchange capacity of a compacted Kahrizak landfill clay liner. The results show that 4% nanoclay significantly reduces permeability (3 × 10?9 to 7.74 × 10?11 cm/s in neutral, 3.66 × 10?9 to 7.9 × 10?10 cm/s in acidic, and 3.25 × 10?9 to 5.24 × 10?10 cm/s in alkaline condition), and increases compressive strength (by 36.28%) and the percentage of swelling (from 16.67 to 41.82, 23.33 to 45.45, and 15 to 38.18 at pH 7, 4.8, and 9, respectively) compare to raw clay samples. Moreover, the results of cation exchange capacity tests show that adding 4% nanoclay to the Kahrizak clay, permeated with landfill leachate, helps the sample maintain its mono‐valent ions between layers and remains dispersed. The results of SEM and XRD analyses show that by adding nanoclay, nanoclay clusters are formed in the sample; as a result, the interlayer spacing decreases which makes it remain dispersed. XRF analyses also demonstrate that by adding nanoclay to the mixture, the permeability and therefore, the amount of heavy metals which can penetrate into it decreases. The results justify the construction of clay barriers with nanoclay in order to prevent leachate penetration, and consequently reduce the operation costs. 相似文献
66.
A modification to the nonlinear Pastor–Zienkiewicz–Chan (PZC) constitutive model without any change in the number of model parameters is introduced in order to simulate stiffness degradation of dense sands at dynamic loading. The PZC model is based on generalized plasticity and was verified by good prediction of liquefaction and undrained behavior of saturated sand. The PZC is a robust model that can predict drained dynamic behavior of sands, especially stiffness increase in loose sand at reloading of dynamic loading. Yet, this model does not show stiffness degradation of dense sand at reloading. The modification is made through modifying the stress memory factor, H DM, which is multiplied by the plastic modulus, H L. This modification does not influence reloading behavior of loose sand. The modified PZC model is verified via results of drained cyclic tests. Two cyclic triaxial tests on loose and dense specimens, along with two cyclic plane strain tests on dense sand are utilized for validation. The model simulation shows that the modified PZC model is able to predict the stiffness degradation of dense sand at reloading well. 相似文献
67.
Using the Sagdeev pseudo-potential technique, further investigation on the effect of nonextensive hot electrons on finite amplitude nonlinear low-frequency electrostatic waves in a magnetized two-component plasma have been reported in detail. The plasma model consists of cold ions fluid and nonextensively distributed electrons. The existence domain for the nonlinear structures have been established analytically and numerically. Apart from the compressive and rarefactive soliton solutions that have been reported earlier, the present investigation shows that double layer structures can be obtained for certain values of nonextensive electrons in the supersonic Mach number regime. The present results may provide an explanation for the observed nonlinear structures in the auroral region of the Earth’s magnetosphere. 相似文献
68.
Analysis of geological structure and anthropological factors affecting arsenic distribution in the Lahore aquifer,Pakistan 总被引：1，自引：0，他引：1
Akhtar Malik Muhammad Tang Zhonghua Zakari Sissou Bahaa Mohamadi Muhsan Ehsan 《Hydrogeology Journal》2016,24(7):1891-1904
This study investigated the potential factors affecting arsenic concentration in the groundwater system of Lahore, Pakistan. The effects of several factors such as population density (PD), pumping rate (PR), impermeable land use (LU), surface elevation (SE), and water-table elevation (WL) on arsenic concentration were studied in 101 union councils of Lahore. Forty single and multi-factor models were established using geographic information system (GIS) techniques to develop an arsenic contamination map and to investigate the most effective combinations among factors. Additionally, statistical tests were used to evaluate arsenic concentration between classes of the same single factor. The arsenic concentration in the Lahore aquifer varied from 0.001 to 0.143 mg L?1. The highest arsenic concentrations were detected in the Walled City and the town of Shahdara. Among the 40 raster models, groundwater arsenic concentration showed the best matching frequency with single-factor models for PD (50.70 %) and SE (47 %). Thus, PD and SE were used to develop an arsenic distribution raster map, and they were also used to study the effect of aquifer depth on arsenic concentration. PD was found to have hidden latent variables such as PR and LU. The shallow aquifer depth was negatively correlated with arsenic concentration (r?=??0.23) and positively with PR (r?=?0.15). Therefore, when there was high PR in wells with smaller aquifer depth, the arsenic concentration was high. The existing water treatment and alternative water resources are good options, which should be developed to deal with Lahore wells contaminated with arsenic at high concentrations. 相似文献
69.
Matthieu J. Talpe R. Steven Nerem Ehsan Forootan Michael Schmidt Frank G. Lemoine Ellyn M. Enderlin Felix W. Landerer 《Journal of Geodesy》2017,91(11):1283-1298
We construct long-term time series of Greenland and Antarctic ice sheet mass change from satellite gravity measurements. A statistical reconstruction approach is developed based on a principal component analysis (PCA) to combine high-resolution spatial modes from the Gravity Recovery and Climate Experiment (GRACE) mission with the gravity information from conventional satellite tracking data. Uncertainties of this reconstruction are rigorously assessed; they include temporal limitations for short GRACE measurements, spatial limitations for the low-resolution conventional tracking data measurements, and limitations of the estimated statistical relationships between low- and high-degree potential coefficients reflected in the PCA modes. Trends of mass variations in Greenland and Antarctica are assessed against a number of previous studies. The resulting time series for Greenland show a higher rate of mass loss than other methods before 2000, while the Antarctic ice sheet appears heavily influenced by interannual variations. 相似文献
70.
Hydrological models are necessary tools for simulating the water cycle and for understanding changes in water resources. To achieve realistic model simulation results, real-world observations are used to determine model parameters within a “calibration” procedure. Optimization techniques are usually applied in the model calibration step, which assures a maximum similarity between model outputs and observations. Practical experiences of hydrological model calibration have shown that single-objective approaches might not be adequate to tune different aspects of model simulations. These limitations can be as a result of (i) using observations that do not sufficiently represent the dynamics of the water cycle, and/or (ii) due to restricted efficiency of the applied calibration techniques. To address (i), we assess how adding daily Total Water Storage (dTWS) changes derived from the Gravity Recovery And Climate Experiment (GRACE) as an extra observations, besides the traditionally used runoff data, improves calibration of a simple 4-parameter conceptual hydrological model (GR4J, in French: modèle du Génie Rural à 4 paramètres Journalier) within the Danube River Basin. As selecting a proper calibration approach (in ii) is a challenging task and might have significant influence on the quality of model simulations, for the first time, four evolutionary optimization techniques, including the Non-dominated Sorting Genetic Algorithm II (NSGA-II), the Multi-objective Particle Swarm Optimization (MPSO), the Pareto Envelope-Based Selection Algorithm II (PESA-II), and the Strength Pareto Evolutionary Algorithm II (SPEA-II) along with the Combined objective function and Genetic Algorithm (CGA) are tested to calibrate the model in (i). A number of quality measures are applied to assess cardinality, accuracy, and diversity of solutions, which include the Number of Pareto Solutions (NPS), Generation Distance (GD), Spacing (SP), and Maximum Spread (MS). Our results indicate that according to MS and SP, NSGA-II performs better than other techniques for calibrating GR4J using GRACE dTWS and in situ runoff data. Considering GD as a measure of efficiency, MPSO is found to be the best technique. CGA is found to be an efficient method, while considering the statistics of the GR4J’s 4 calibrated parameters to rank the optimization techniques. The Nash-Sutcliffe model efficiency coefficient is also used to assess the predictive power of the calibrated hydrological models, for which our results indicate satisfactory performance of the assessed calibration experiments. 相似文献