Articles in This Issue
Abstract
Mathematical programming techniques have been used to minimize the cost of reinforced concrete T-beam floor. The floor system consists of one way continuous slab and simply supported T-beams. The study presents a formulation based on elastic analysis followed by the ultimate strength method of design with the consideration of serviceability constraints as per ACI Code. The formulation of optimization problem has been made by utilizing the interior penalty function method as an optimization method with the purpose of minimizing the objective function representing the cost of one-meter length of the floor system. The cost includes cost of concrete, reinforcement, and formwork. The design variables considered in this study are the dimensions and the amounts of reinforcement for the slab and beams, in addition to the spacing of the beams. Many examples are solved to show the effect of these design variables on the optimum solution of the floor system. The effect on the optimum design of the compressive strength of concrete, yield strength of steel, concrete cost ratios, and formwork cost ratios has also been studied.
Abstract
تم في هذا البحث دراسة تأثير الرسابات في خشونة القنوات الحصوية القعر حيث تم اجراء التجارب في قناة مختبرية مستطيلة الشكل بطول (10) (م) وعرض (0.3 م) وعمق (0.45 م) باستخدام ثلاثة أنواع من مادة القعر الحصوية وبأقطار تتراوح بين (0.02 - 0.03) و (0.03 - 0.04) و (0.04 - 0.05) م ولدراسة تأثير الرسابات تم استخدام ثلاثة نماذج من الرمل. وتبين من ملاحظة نتائج هذا البحث حصول نقصان في مقاومة الجريان نتيجة تعرض القناة إلى تأثير الرسابات حيث تملأ الرسابات الفراغات المحصورة بين حبيبات مادة القعر بصورة تدريجية مسببة تناقصاً في معامل خشونة القعر إلى الحد الذي تملأ فيه الرسابات كافة الفراغات المحصورة بين حبيبات مادة القعر. وتم في هذا البحث استنباط معادلة وضعية لتقدير معامل ماننك والتصريف الحقيقي بعد تعرض القناة الى تأثير الرسابات، وقد أعطت هذه المعادلة تطابقاً جيداً مع القيم المقاسة بحيث لم تتجاوز نسبة الخطأ في تقدير معامل مانتك عن (7.3%).
Abstract
This research has been conducted in order to evaluate the compression index of Gypsiferous soil. A series of consolidation experimental tests with different percentage between 5% - 20% of gypsum added to the soil have been performed. From results. It had been seen that with increasing percentage of gypsum the compression index increased, with a maximum percentage of 30.4%.
Abstract
In the present study, the dynamic analysis of jacket type offshore structures under the action of sea waves is carried out. The finite element method is adopted for the solution of the problem. The effect of soil-structure interaction on the dynamic behavior of the offshore structure is taken into account due to the deformations of the soil caused by the motion of the structure, which in turn modify the response of the structure. The supporting elastic foundation is represented by Winkler type model having normal and tangential moduli of subgrade reaction. These moduli may be constant or varying linearly or nonlinearly along the embedded length of the piles that support the offshore structure. The pile tip conditions are also considered. A time domain solution is recommended. The generalized Morison's equation is used to calculate the wave forces and Airy's linear theory to describe the flow characteristics. Both free and forced vibration analyses are studied. The dynamic response has been obtained by modal analysis in conjunction with Wilson-θ method. As an example, a modified model of an actual jacket type offshore platform is analyzed under the action of wave forces.
Abstract
This paper presents a PWM AC/DC buck converter circuit incorporating a frontend rectifier followed by a DC/DC converter. Two transistors are used as a main and auxiliary switches. The proposed circuit provides zero-current (ZC) turn ON and zero-current/zero-voltage (ZCZV) turn OFF to the two transistors, besides zero-voltage turn ON to two diodes. Numerical methods are used to analyse and determine the performance of the converter system. A feed forward technique is employed to improve the performance of the converter over a range of output power.
Abstract
This paper considers the neural network based PID controller. The learning and generalization properties of neural network are utilized in improving the performance of a conventional PID controller. Two different schemes are introduced. Both schemes are studied and their performances are comparatively evaluated on an example for uncertain system.
Abstract
The influence of time delay on the statistical behavior of the first-order phase-locked-loop is investigated in VHF and UHF synchronous communication systems. The Fokker-Plank equation has been proposed to estimate the probability density function (pdf) of phase fluctuations as well as the average time to loss lock in the presence of noise. The result reveal that the degradation in the loop performance occurs under various conditions of detuning when the inherent time delay is present
Abstract
The use of fiber-optic links as the connecting media in wireless microcellular networks can be provide uniform radio coverage to spatially distributed mobile users in cost effective manner. This paper investigates theoretically the performance of fiber distribution system for mobile phone networks that uses a single high power Nd:YAG laser in the base station and shared by many microcells. Analytical expressions are derived for the bit-error-rate (BER) floor characteristics and optimum operating conditions. The results indicate clearly that the laser power can be reduced significantly when the modulation index is optimized.
Abstract
The main objects of this investigation are to obtain convenient expressions for the estimation of discharge coefficient for submerge flow over concave and convex semicircle shape crested weirs. Sixteen weir models were constructed and tested. these, models were classified into four groups. The first and second groups were of single cycles having concave and convex shapes, respectively, with curvature radius of 15cm. The third and forth groups were of double cycles having concave and convex shapes, respectively, with curvature radius of 7.5cm.in each group the weir height, p was varied four times 10cm, 7.5cm, 5cm and 2.5cm Based on results of this study it was found that for constant weir radius, R, the discharge coefficient, Cd, increases with the increase in the relative upstream head, h/p, while, for constant upstream bead, weirs of small heights give higher discharge coefficient than those of large height Two general expressions were obtained for the estimation of Cd as function of, relative upstream head, h/p and relative radius, R/P, one expression for single and double cycle concave submerged weirs and the other for convex submerged weirs.
Abstract
This study concems with the improvement of soils in Basrah area. Two types of soil have been selected; the first from Garmatt Ali place and the second type from Abu Al-Khasseeb place. Natural (palm) fibers are used in stabilization of these soils. These fibers were added by different percentages (0, 1, 2, and 3%) by weight of dry soil so as to improve soil properties. The selected soil are subjected to different tests such as liquid and plastic limit, specific gravity, unconfined compressive strength, compaction test. It was found that the addition of fibers to the soil affects compaction characteristics by decreasing maximum dry density and increasing optimum moisture content for both types of soils. The unconfined compressive strength increased with more addition of fibers The affect of fibers content on swelling, the swelling percent reduced especially during first days of the test.