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244.
ATM Sakiur Rahman Md. Kamruzzama Chowdhury Sarwar Jahan Quamrul Hasan Mazumder 《Journal of the Geological Society of India》2016,87(2):179-193
In Bangladesh, agriculture plays a major role in the national economy. In the drought prone Barind area in NW Bangladesh, cropping intensity has increased almost double since late eighties of last century (from 1985) because of the introduction of groundwater irrigation. Long-term behavior of groundwater table (GWT) in the drought prone Barind area has been studied using MAKESENS model in the wake of massive installation of tube-wells. The study reveals that the maximum and minimum depths to GWT during 1991-2010 show on average declining trend of 4.51 m and 4.73 m. The long-term prediction for the period of 2020-50 assuming the current rate of groundwater withdrawal is that the declining trend will be 1.16 to 1.59 and 1.07 to 1.82 times more for maximum and minimum groundwater depths respectively in comparison to the present. The rigorous exploitation of groundwater for irrigation, decreasing rainfall and surface geological attributes lead towards declining trend of GWT. This will hamper the country’s food security and ultimately threaten its socio-economic sustainability. So the appropriate strategies for the management of groundwater resource on a sustainable basis should be the priority for maintaining agricultural productivity. 相似文献
245.
Utilization of bituminous limestone ash from EL-LAJJUN area for engineering applications 总被引:1,自引:1,他引:0
The following work aims at minimizing the environmental impact of the solid wastes (ash) that is produced after the utilization
of the bituminous limestone in thermal power stations and /or retort processes. Limy ash has been prepared from the El-Lajjun
bituminous limestone by direct combustion at 1,200, 950, and 525°C respectively. The laboratory tests have been selected with
respect to construction needs and possible post construction conditions. Utilization of the various types of ash in the stabilization
problematic soils from Jordan as brown soils and the clayey marl has revealed optimum results. The unconfined compressive
strength of the parent brown soil and the clayey marl has been raised from 5 kg/cm2 to 50 and 25 kg/cm2, respectively. The CBR value has been raised from 4.5 to 150% for both problematic soil types. Various mortars and construction
elements can be produced at normal room curing temperature without the use of ordinary Portland cement (OPC). Low quality
sub-base and base course can be mixed with ash to produce cement treated base (CTB) and roller compacted concrete (RCC) without
OPC. Durable pavements, embankments can be constructed with very long life and low cost. CTB and RCC utilizing ash can be
used in dam construction instead of normal soil in earth fill dams. The high alkalinity of El-Lajjun ash is considered as
a disadvantage to be utilized in normal concrete mixes for structural purposes. Ash only can be mixed with aggregates to produce
lean concrete like for blinding purposes to be prepared for foundation activities. 相似文献
246.
Flow‐through column experiments were carried out to investigate the influence of pH on the sorption of three phenols (2‐methyl‐4, 6‐dinitrophenol, 2, 4, 6‐trichlorophenol, pentachlorophenol) onto a natural sandy aquifer material collected from a bank filtration site of River Elbe, Germany. For the phenols investigated, an increase in sorption (retardation) with decreasing pH is observed indicating a stronger sorption of the neutral species in comparison to that of the anions formed by dissociation. The anions of 2‐methyl‐4, 6‐dinitrophenol and 2, 4, 6‐trichlorophenol do not show significant sorption. On the contrary, pentachlorophenol showed sorption not only in neutral form but also in ionic form significantly which should be taken into account while assessing the fate and transport of such compound. A linear model based on the degree of protonation (calculated from pH and pKa) can be used to resolve the apparent (observed) sorption coefficient (Kd, app) into its neutral (Kd, n) and ionised (Kd, i) components. Knowing pKa, Kd, n, and Kd, i the apparent sorption coefficient for pH values other than experimentally investigated can be predicted. 相似文献
247.
Matiur Rahman 《Ocean Engineering》1987,14(1)
An approximate analytical analysis is demonstrated in this research note to obtain the approximate wave forces on rectangular caissons fixed vertically on the sea-bed. A data plot has been depicted to show the effect of linear forces for the case of rectangular caissons and that for the case of square caissons. 相似文献
248.
Mohammad Mahfuzul Islam M. Reaz H. Khondoker Chowdhury Mofizur Rahman 《Ocean Engineering》2001,28(12)
The paper describes a methodology for automatic hull form generation of ships with some desired performances using artificial intelligence techniques. The whole implementation process is divided into three main components. First of all the half-breadth weight matrices are generated that would provide population with pre-fitness by examining the relationship of the hull form with the principal dimensions of a number of existing vessels. Secondly, breadth and draft are adjusted using Neural Network Concepts. Breadth, draft, length, displacement and speed of the ship are very related terms and relations among them create some constraints. Neural Networks solve these constraints and adjust the parameters. Finally, Genetic Algorithm is used for searching the exact solution by examining several generations. For this, the algorithms need to measure fitness for every population in every generation. Unfortunately, GA doesn't guarantee fairness of the surface of the hull form, which can't be ignored. So, for every population especially for newborn population fairing techniques would be used. However, being complex geometric shape, hull form surface can't be faired using least-square or other single equation fitting techniques. Fairness is done taking pair-wise points using B-spline functions [CAD 20(1988)]. 相似文献
249.
Based on the linear diffraction theory, an investigation is made on the interaction of water waves with a completely submerged sphere in water of finite depth in this paper. The method of multipole expansions is used to obtain the fluid velocity potential in the form of double series of the associated Legendre functions with the unknown coefficients of the infinite set of infinite matrix equations. The truncation property of the matrices and the convergence of the multipole series coefficients are investigated for various wavelengths and depths. The systematic numerical simulation, based on our analytical solution, is carried out and the fields of the hydrodynamic diffraction pressure and fluid velocity around the sphere, the three-dimensional free surface elevation, and total exciting forces acting on the sphere are graphically presented for a wide range of the body submergences, ocean depths and wavelengths. 相似文献
250.
M. Rahman 《Applied Ocean Research》1984,6(2):90-100
An exact second order theory has been formulated in this paper to calculate the wave forces on offshore structures. Lighthill's method for deep water waves has been extended to shallow water waves. Exact expression for linear velocity potential applicable to the circular cylindrical strcutures for shallow water waves have been used in these calculations. These results have been verified with those obtained by direct perturbation technique reported recently by Rahman and Heaps. It is interesting to note that both the methods yield identical results. 相似文献