University of Thi-Qar Journal for Engineering Sciences

Impervious core is used in zoned earth dam to reduce the quantity of seepage through the body of the dam and to relief part of risk of piping and erosion in the downstream side. This paper presents cases study of the effect of core permeability, thickness and location on the flow through large earth dam. Finite element method was used to solve the problem of flow of incompressible fluid which is governed by Laplace equation. A considerable range of shell permeability to core permeability was used. The study has shown that quantity of seepage was reduced as ratio of shell to core permeability increases. The reduction in seepage continues to a limited value of core permeability after which the effect decreases. Doubling the core base thickness reduces the quantity of seepage highly and inclination of core towards upstream side slightly increases the quantity of seepage.

It is well known that the anodized thin layer formed on Al-alloys surface are characterized with porosity of nanometric dimensions whatever acid or alkaline solutions are used. In this study, an attempt was made for the first time to develop a new method for obtaining anodized multilayer film by reinforcing the anodized oxide coating with incorporating nanosized graphite in the layer structure during anodizing process by means of anodizing Al- Alloy type 7075 T-6 in an electrolyte composed of water solution of chromic acid and graphite . This leads to obtain a multilayer anodized film having good thickness and high micro hardness properties. Nanosized particles of graphite have been formed into anodic oxide layer. The influence of anodizing process parameters (voltage and current density) on the thickness micro hardness and chemical composition of a multilayer oxide film are determined.

In this paper a numerical investigation is made to study the axially symmetric, laminar air flow in the entrance region of an annulus by solving the two dimensional governing equations of motion ( continuity, momentum & energy ) using implicit finite difference method and the Gauss elimination technique. A STAR CCM + program is used. The results obtained for velocity and temperature profile revealed that, the secondary flow created by natural convection have a significant effect on the heat transfer process. A comparison has been made for results which show a good agreement.

Orthogonal frequency division multiplexing (OFDM) is an attractive technique for modern wireless communication. One major drawback of orthogonal frequency division multiplexing schemes is the high peak to average power ratio (PAPR) of the output signal. Selecting mapping (SLM) and partial transmit sequences (PTS) are two important techniques for reducing PAPR, but they need to transmit side information to indicate how the transmitter generates the signals. In this paper, we proposed an efficient technique to reduce PAPR in OFDM system. For this technique, circular shifter used to produce K cyclic sequences from the same information sequence. These sequences XOR with K randomly generated keys, the same keys used in receiver side to detect data. The sequence with the lowest PAPR among K sequences is chosen for transmission. Side Information (SI) is coded using Hamming code and embedded into the information sequence. Computer simulation tests have been applied on BPSK and N= 64 subcarriers OFDM system with the proposed method. Moreover, this system will be evaluated under the effect of AWGN channel. The results exhibit the ability of such technique to reduce the PAPR without major effect on the system performance as compared with the conventional OFDM technique. The PAPR of OFDM signal is further reduced by 4–5 dB by this technique.

In this paper the code DEFORM-3D V6.1 was used to perform a finite element analysis simulating the turning process of AISI 1045 carbon steel. A series of thermal simulations have been performed, the value and location of maximum temperature have been determined. The comparison of the simulations with earlier works gave promising trend for the presented work with a maximum percentage of error 3.23%. The results of this work show that the maximum temperature exists in the vicinity of the cutting edge. i.e. in the tool-chip contact and then starts cooling immediately when the tool crosses this region. Besides the maximum temperature in the tool-chip interface increases as the cutting time increases until the process reaches the steady-state condition where the temperature is alternating around the mean temperature. Finally the behavior of temperature differs in value and distribution for the same location and time (same boundary conditions) in the cutting direction with the change in depth of cut where the maximum temperature occurs at maximum depth of cut.

In this work the temperature rise in AL7075 wire drawing is predicted numerically using a 3D finite element model. The commercial code Deform-3D was used to construct the model and simulate the wire drawing process. Aluminum wire of 46.38mm was drawn at room temperature through a conical die with semi-die angle α=5°and percentage reduction in area equal to 10%. This case was run for different values of friction coefficient (μ=0.05, 0.075, 0.1, 0.125, 0.15, 0.175, 0.2). The result shows that as the coefficient of friction increases, the temperature rises in linear form. The behavior of temperature rise distribution is studied in details for μ=0.1, for this case the temperature rise in wire during the drawing process is (22.3Co) less than in die (28.7Co), also the location of maximum temperature in the die occurs at the contact area before wire exit from the die.

Partial Transmission Sequence (PTS) method proposed is one of the methods to reduce the Peak to Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) system. In which each symbol of OFDM in the frequency domain is divided into sub blocks and each one, multiplied by a phase factor to rearrange the origin symbol to a version with the lowest PAPR. This method is based on changing the phase of each sub blocks to reduce the probability of occurrence high PAPR. The nonlinear behavior of the phase affect's the accuracy of reduction which makes it different as compared with this method. In this paper, a proposed method is suggested to reduce the complexity of such method .

The power chimney tower is one of modern promised energy which may be developed by low losses, simple and has high facilities. In this paper, many parameters were studied for prediction of system operation. Velocity distribution is the important parameter which gives the first prediction to put the position of erection of power turbine, made or not. The numerical analysis was presented by using GAMBIT and FLUENT 6.3 to predict that high velocity at the expansion of chimney near the solar collector place. This position is very suitable for promoting and building the power turbine since the velocity range was between (33 - 54 m/s) for different solar flux 200W/m2, 400W/m2, 600W/m2 and 800W/m2. So, the other factors, temperature and pressure were studied to coincide with previous papers in this field.

Galvanized steel stranded ropes ( 10.3 mm diameter ) were welded by brazing and soldering , also stranded copper cables ( 9.5 mm diameter ) using Socket – Butt joint with capillary gap between 50 – 100 um , and 2 mm butt gap . Welding was completed by torch technique with commercial fluxes . The filler – metal alloy are copper – phosphors for brazing and tin-lead eutectic for soldering . The bonding mechanisms are generally the same . Bonding phase I will be created at the interface , while the intermediate phase II is the remainder . Mechanisms are different in spreading , wetting and bonding strength .

This paper investigates the use of statistical control techniques such as (statistical control charts and process capability) in quality control of the electrical wires and cables which were produced in Ur Company (Cable factories) and in order to evaluate the performance of the manufacturing machines. Two types of manufacturing processes were selected namely (drawing and insulation) by testing diameter, max. tensile strength, elongation, and electrical resistance of wires, and testing of nominal thickness, strength, and elongation of insulation and sheathing of cables, for evaluating of quality control and process capability by using control charts namely (Average-Range) chart and process capability calculations and statistical analysis based on histogram technique. The results showed that some of machines are unable to satisfy the specification tolerances due to wide differences in the resulted values of the statistical parameter. Therefore, it is important to carry out the total maintenance for these machines, and increase the quality control activities such as testing the raw materials by chemical analysis.