AL-Rafidain Engineering Journal (AREJ)

The types of corrosion protection on corrosion resistance of steel pipe samples buried in soil have been studied in this research. Samples of unprotected carbon steel are used with other protected by different corrosion protection such as galvanic coating, rubber coating and two types of cathodic protection (impressed current and sacrificial anodes). The weight loss technique is used as a function of the corrosion rate (mdd). The results, which have been obtained, show that the corrosion rates in the unprotected samples are high compared with the corrosion protected samples, and the maximum corrosion resistance is found to be at the cathodic protection systems

This study presents a numerical analysis of push-off and modified push-off fibrous concrete specimens. The investigated variables were, volume fraction of fibres, area of reinforcement, and the ratio of the compressive to the shear stress. Eight nodes isoparametric elements were used to represent concrete, and embedded bar elements to represent the reinforcement. The nonlinear behaviour of fibrous concrete in compression, tension and the reduction of the shear modulus due to cracking were taken into account.The numerical results showed good agreement with the experimental results, the average ratio of the calculated to the experimental first crack shear stress is (0.955), and the average ratio of the calculated to the experimental shear strength was (0.981). The cracks patterns showed that the fibrous specimens have less numbers of cracks than that of plain specimens at a certain shear force, and the presence of fibres delay the initiation the cracks. The calculated slip is slightly more than the experimental slip at early stage of loading and the difference increased prior to the failure load.

In the present work, the finite element method has been used to investigate the behavior of fibre reinforced concrete slabs in the pre and post-cracking levels up to the ultimate load. Assumed transverse shear strain is used in the formulation to overcome the shear locking, and Heterosis elements are employed in the analysis. Both an elastic-perfectly plastic and strain hardening plasticity approach have been employed to model the compressive behavior of the fibre concrete. The yield condition is formulated in terms of the first two stress invariants. Concrete crushing is a strain-controlled phenomenon, which is monitored by a fracture surface similar to the yield surface. A layered approach is adopted to discretize the concrete through the thickness. A tension stiffening model has been suggested by making a regression analysis of the experimental results, with index of determination (90.61%). The steel is considered either as an elastic perfectly plastic material or as an elastic-plastic material with linear strain hardening. Steel reinforcement is assumed to have similar tensile and compressive stress-strain relationship.

In the recent years, the uses of the binding materials of different types in addition to cement become very wide in the product of concrete as blending of portland cement with limestone, so it is necessary to investigate the influence of the binder material on the concrete properties. In order to asses the performance of this type of concrete, it is important to understand the changes in the concrete properties especially in case of exposure to elevated temperature.This paper summarize and discuss the effect of the limestone powder (CaCO3) as a compensating material with cement on the compressive and tensile strength and discuss the effect of elevated temperature on this type of concrete.Limestone powder (LP) was used as a compensating material with different ratio of cement include (0, 10, 15, 20, 25) %. Compressive and tensile strength were investigated before and after the exposure to high temperature including (200, 400, 600) °C.The study show that limestone compensate changes in both compressive, and tensile strengths. Negative effects on the properties observed as the amount of limestone exceeds 15% of the cement weight. After the exposure to high temperature the results show a drop in compressive and tensile strengths in a different form.

This paper deals with the tensile behaviour and strength of cast-in-place short headed anchor bolts embedded in both normal concrete (NC) and steel fibre reinforced concrete (SFRC). Four volume fractions (vf =0.4%, 0.8%, 1.2%, and 1.6%), two aspect ratios (lf / df =19.63, 36.33), three bolt diameters (db =8, 10, 12mm), and four embedment depths (hef =25, 37.5, 50, 62.5mm) were used. More than (108) specimens were tested under monotonic tensile loading. Only (90) specimens were failed by large concrete failure cone exceeding the dimensions of the specimen and the cone breaks into pieces in most cases (concrete failure), while the other specimens were failed by yielding or fracture of the bolts (steel failure). Tests results showed that breakout capacity ( ) of the anchors were significantly enhanced by the addition of steel fibers to concrete and the size of the failure cone in (SFRC) specimens were smaller than the size of failure cones in (NC).

In this paper the effect of high temperature on plain concrete strengthened with Carbon Fiber Reinforced Polymer ( CFRP ) sheets and behavior of concrete strengthened after heating were studied for flexure and compression properties . For this purpose a total of 44 prismatic specimens of 100x100x350 mm dimensions were tested . Results indicate that due to high temperature there is a continuous reduction in flexural strength of concrete strengthened with CFRP sheet . Deflection corresponding to flexural strength also reduced for exposure temperature higher than 350oC . The effect of finishing CFRP layers with cement mortar for controlling the reduction of flexural and compressive strengths due to high temperature was found to be not important . According to the obtained results , plain concrete damage by high temperature can be repaired using CFRP sheets for compressive strength of about 74% of that of plain concrete , and flexural strength of about 69% of that of strengthened concrete before heating

A proposed method of Macrocell / Microcell channel selection in multitier cellular system using sojourn time of microcell overlapped region. To keep the handoff rate to acceptable level, low mobility users (with speed V < Vth) should undergo handoffs at microcell boundaries and high mobility users (with speed V > Vth) should undergo handoffs at macrocell boundaries. Investigation of variation of the number of channels in the microcells and the macrocell with the blocking probability. Also the variation of microcell radius on the blocking probability for different mobile stations speed.

Literature survey indicates that the design of sequence generator is considered for a few number of control sequences of stepper motor. In our research a new circuit is built in a simple design for generation of all required sequences up to eight phases for Variable Reluctance (V.R.) stepper motor .This circuit must be followed by a power drive circuit to achieve the power requirement of the stepper motor. In case of getting a certain sequence , these data must be given to the system ; number of phases, number of 1st energized phases, type of sequence (full step or half step mode) and finally the direction of rotation, hence the system in response will generate the required sequence. Some papers previously used SSI & MSI circuits to build the sequence generator ,but in this paper an LSI (EPROM) circuit as well as SSI & MSI circuits are used to get minimal design with less components. The paper includes a brief description of the fundamentals of sequences controlling the stepper motor, the detailed proposed circuit description and samples of experimental results with an appendix illustrating a complete map of the EPROM which is used to store all required sequences.

The objective of work is to find the scale of ring array antenna for localizing field intensity at certain focal point. The study is interested in comparison between focusing by setting a scale factor of array antenna to cohere (synchronize) waves of electric field when reaching focal point, and focusing by compensating phase differences that was initiated from ray length differences between waves reaching focal point. Isotropic sources are used for simulation. These sources are distributed along a circular ring, each ring of array rings is complement with the previous rings, that means it has a phase complement to a complete cycle ( )

This paper proposes a new image steganography scheme in order to hide a secret data in cover image uses the transform domain to increase its robustness and security. Curvelet transform is the new member of the evolving family of multiscale geometric transforms. Since it represents edges better than Wavelet, Curvelet transform offers an effective solution to the problems associated with image steganography using Wavelets and DCT (Discrete Cosine Transform). In this paper we were testing four different steganographic methods. The Radon Transform used in this paper for encoding the secret image to increase security. The software used in this paper is (Matlab V 7.0.4). The results obtained are in accordance with the expected predictions of the existing theory of Curvelet transform.

This work investigates the evaluation performance of detection system for Frequency Hopping (FH) signals based on Fast Fourier Transform (FFT) with proposed decision circuit based on Adaptive Threshold Level (ATL), where the threshold level changes its value automatically without manual intervention depending on the estimated values of (SNR) in the channel, the level will be high when the noise is high and vice versus. A comparison in evaluation performance were made with a conventional mode where the decision circuit based on Manually Change Threshold Level (MCTL) done by the detector according to its observation on sensing the Signal to Noise Ratio (SNR). The results shows that the proposed mode (adaptive) is give best results for probability of detection PD and probability of false alarm PF comparing with the (Manually Change). Also the results of (adaptive) are compared with that theoretical computation and gives a very small error for high noise while vanish for low noise.

This research represents an attempt to solve a problem introduced by Ninevah drug factory to increase the out put of one of its laboratory machine located in research sector . First of all, thinking was for selection a suitable material of punches and die compatible with the surrounding environments of different drug powders as they represents corrosive agents to the metal that in touch .Beside that this material primarly must be capable of being machined to manufacture the required design, Also it is capable to be heat treated after manufacturing . Second ,we should redesign the punch and die with the same surrounding spans limitation but with increasing the number of used punches and redistributing them in a suitable manner in its restricted die, and manufacturing punches with a different sizes (7, 9, 7.9,10.3,12.53 )mm in diameter as the factory demand taking into account the concave and convex of pair of punches to create the mirror shape of tablet after pressing is completed . All that will be done must give the standardized weight , size and optimum compressibility according to the certificate of the quality control unit.

The Knelson concentrator is a centrifugal separator which was originally and successfully designed for extracting free gold particles. Despite of its wide range of applications, the exact concentration mechanism of the device is not fully understood. The purpose of this research was to determine the optimum parameters and improve the performance of knelson concentrator by investigating the effects of artificial porous beds and pulsed water jackets on the performance of the device.Artificial bed consists of glass beads of range 1.5-2 mm diameter have been used. It was found that two techniques can improve the performance of the batch Knelson concentrator. The experimental work showed that improvement ratio of concentrator was increased about 1.55 for flow rate 8 l/m compared with no bed for the same flow rate. In addition, the improvement ratio was increased about 1.25 when pulsed water was used. Another purpose of this work was to develop mathematical model approaches to understand the fundamental mechanism of the Knelson concentrator.In addition, two mathematical model of the Knelson concentrator have been developed.

The main purpose of traditional broad - crested weir is to rise and control upstream (U/S) water level. In this study a new performance was added to this weir, by making it as an energy dissipater. In order to study the energy dissipation percent (E%), the downstream (D/S) height of the weir (12 cms U/S height) was reduced four times as 9.8,8,6and3.8cms.Thirty experiments were performed in a laboratory horizontal channel of 12 m length, 0.5 m width and 0.45 m depth for a wide range of discharge. A mathematical model to compute theoretical coefficient of discharge (Cdth) was modified depending upon momentum equations. Experimental results gave a high validity to the computed values of the proposed model. On the other hand, three empirical non dimensional relations were obtained. The first is liner relation to estimate the ratio for D/S water head to U/S weir height (h/P1) in terms of the ratio for U/S water head to U/S weir height (H/P1). The second relation is nonlinear relation to estimate the discharge coefficient (Cd) in terms of H/P1 and the ratio of D/S weir height to U/S weir height (P2/P1). While the third relation is to estimate E% in terms of h/P1and P2/P1 with high correlation coefficients. The experimental results of the study showed that E% increased up to 46%. Furthermore, Cd was improved and gets higher values in comparison with traditional weirs.