University of Thi-Qar Journal for Engineering Sciences

The performance of photovoltaic cell is affected by the value of its tilt angle with respect to horizontal plane, where the variation of tilt angle changes the amount of solar radiation permit to the photovoltaic cell surface. So that, the using of solar tracking system for photovoltaic cell will get the maximum solar radiation that permit to the surface of the cell at any time and day of the year, but the solar tracking systems have high operation and maintenance costs and are not always applicable. It is often convenient to set the solar collector at an optimum fixed tilt angle over a time of the year with less reduction in solar radiation received in the cell surface.This work is to find an optimum tilt angle of photovoltaic cell located in southern Iraqi cities Basrah city (latitude 30.30), Amarah city (31.55) and Nasiriyah (31). A mathematical models was used and programed by engineering equation solver EES to find an optimum tilt angle depending on the maximum solar radiation, the tilted angle varied with range from 0 to 90. The results showed that the optimum tilt angle for Basrah is 28, where for Amarah is 30 and for Nasiriyah is 29.

Present study was conducted at Tigris river, near Wasit Thermal Power Plant (WTPP) in Al Zubiadiyah city to evaluate the impact of discharging domestic sewage during construction period(2010-2016) on water quality of the river; to assess the level at which effluents discharged from WTPP affect the quality of Tigris river water; and to compare the quantity of pollutants in the water with the acceptable limits of Iraqi Standards. Observation recorded during the three months study depicted that the river is polluted in certain areas downstream the river as comparatively higher values of biological oxygen demand (BOD) and chemical oxygen demand (COD) were recorded. The level of total dissolved solids (TDS), dissolved oxygen (DO), chemical oxygen demand (COD), biological oxygen demand (BOD), total hardness, sodium ion, and sulfates (SO4) in the water sample were quite high. With the exception of pH, all other physical-chemical parameters measured are between 100% and 180% higher and have exceeded the maximum permissible limit given by the permissible Iraqi standards. The domestic wastewater is discharged directly to river without any treatment during this period (construction period), there is tendency of these pollutants to persist in the water and its uptake may cause long term health problems when the water is used as drinking water, especially in areas near the point of discharge, since there is an intake of a water compact unit 1 km downstream from the point of discharge (Al-Bokhauder village ), as well as the adverse effects on plants when the contaminated water used for plant irrigation .

Dynamic analysis of coaxial dual rotor system was demonstrated in this paper through the use of finite element script files developed using matlab. A coaxial rotor system, generally employed in the aircraft engines to save space and keep the weight to minimum, and for the importance of this application it was considered for this analysis. The system was modeled using eight finite elements only with different shafts and bearings properties. The results obtained in this investigation were closed to other previous studies found in the literature. The developed matlab script files proved to be very essential for designers and analyst of coaxial rotors.

The behavior of composite beams with circular web openings is described. Four composite beams comprising one control beam were tested. The perforated beams have six circular openings with various locations. Opening size was fixed (66.7% of the steel section web depth) while number of openings in each composite beam was varied. Deflections at midspan and at openings were observed. Cracking of concrete slab and behavior of each opening were explained in detail. Tests indicated that circular web opening reduced the strength of composite beams. The behavior of composite beams relatively unaffected by the presence of circular web openings up to first yield. Less effect for the inclusion of circular web openings located out of midspan. The concrete slab has limited contribution to the strength of composite beams with circular web openings.

The present work investigates the influence of fuel injection pressure on the combustion and emission characteristics of ultra-low diesel fuel for high speed direct injection ( HSDI) diesel engine at different fuel injection timings( -12,-9,-6,-3,0 ) ATDC has been made . The fuel injection pressure were(800,1000,1200) bar and at high load ( 80Nm= 5BMAP) , low load ( 40Nm=2.5BMAP ) , With constant engine speed ( 1500rpm) . In-cylinder pressure was measured and analyzed using LABVIWE program .A calculation program specially written in MATLAB software was used to extract the apparent heat release rate, the ignition delay, combustion duration and specifies the amount of heat released during the premixed and diffusion combustion phases ( premixed burn fraction PMBF) and ( diffusion burn fraction DBF). The influence of injection pressure on the exhaust emissions such as carbon monoxide (CO), total hydrocarbons (THCs), nitric oxides (NOx), smoke number (SN) and fuel consumption were also investigated.A result referring to that when the injection pressure was increased, the ignition delay reduced. A shorter ignition delay at high injection pressure also advanced the combustion, and increased the in-cylinder pressure, heat release rate and their peaks respectively .The premixed burn fraction increased with fuel injection pressure increasing, and this caused a decrease in each of the exhaust SN, THC and CO emissions but the NOx emissions increased.

In this paper, A robust adaptive speed sensorless by a neural network approach of a separately excited (DC) motor without the use of speed sensors is presented.The simulation carried out by Matlab backage. The actual speed is estimated using a feed-forward neural network, the neural estimator have three inputs which are armature current, armature voltage, and the speed in the previous step of time; and one output which represents the estimated speed. The obtained results are presented to show the validity and efficiency of sensorless control scheme, which in turn obtains high performances.

This study presents an idealization scheme for the analysis of rectangular storage tanks acted upon by earthquake excitations. Above and below ground tank, are considered. A linear three-dimensional finite element analysis is adopted to predict the natural frequencies. The analysis parameters are the ratio of height to length of the tank, the type of soil, level of water in the tank, and also the wall thickness.Tanks made from steel as well as from concrete are investigated. A general purpose finite element program (ANSYS 12.0)used to model the analysed system. The tank base and wall are modelled by plane strain shell elements. The contained liquid is represented by a special solid element. Finally, the soil is modelled by simple spring-damper elements. The soil medium is idealized by the elastic half space model, that is, linear springs are assumed to represent the structure-soil interface. Which is then modelled by two-node spring dashpot elements.Forced vibration analysis is conducted on above ground and buried concrete tank. This analysis is carried out by applying the records of the North-South component of the 1940 El Centro earthquake with peak acceleration of 0.32g. It is found that the bending stresses in above ground concrete tank is (74.167) % greater than the stresses in buried tank with the same dimensions.

In this paper, the large amplitude of free vibration and buckling of Euler–Bernoulli beam rests on a non-linear elastic foundation subjected to an axial force are studied. Hamilton’s principle is followed to derive governing equation of the beam response. Using an analytical method based on the Galerkin technique,the nonlinear governing equations of motion was simplified to a time-dependent Duffing equation with cubic nonlinearities and then solved using Laplace Iteration Method. Comparison between results of the present work and those available in literature review shows reasonable agreement of this method. Effects of vibration amplitude, elastic coefficients of foundation and axial force on the non-linear natural frequencies and buckling load of beams are presented. Results reveal that decreasing linear and shear parameters and increasing nonlinear parameters of foundation lead to increasing frequency ratio and buckling load ratio. Furthermore, increasing axial force decreases absolute values of both linear and nonlinear frequencies as well as natural frequency ratio.