http://dspace-su.server.ly:8080/xmlui/handle/123456789/1535 2026-05-01T10:24:04Z http://dspace-su.server.ly:8080/xmlui/handle/123456789/1546 Comparison of Experimental and Numerical Heat Losses on Air Conditioned Office in Desert Climate Ali M. Wahhad; Nor Mariah Adam; Mohd S.Salit; Ahmed A.B. Alarabi In recent years, the building community has integrated sustainable design concepts that can improve indoor air quality while conserving energy in buildings. A computational fluid dynamics (CFD) simulation program using three-dimensional flow finite difference of k –ε has been used and compared with experimental results. The study was carried in a new air-conditioned administrative office center built in 2002 as part of Libya’s regional development, as shown in Figure 1. The building is located in Hoon City, province of Al Jufrah, Southern Libya, at lat. 7’ N and lat. 56’ E. Experimentally eight thermocouples were placed at eight different positions on the inner surface to measure the surface inner temperature. The main aim of the study is to evaluate the temperature difference between outdoor and indoor and the distribution of the air temperature and the velocity inside the room. The temperature differences between the indoor and outdoor was found to be varied between 9 °C to15 °C. Good agreement was achieved between the computed and measured results. The error percentage was varied from 0.3% to 0.8%. For both inner and outer surface, good agreement between experimental and CFD heat transfer coefficient has been achieved. 2015-12-01T00:00:00Z http://dspace-su.server.ly:8080/xmlui/handle/123456789/1544 Motor Current Signature Analysis to Detect Static Eccentricity in Case of 300 kW Induction Motor Saleh Elawgali In this paper the current spectrums of a five pole-pairs, 300 kW, squirrel cage induction motor were calculated for the cases of full symmetry and static eccentricity. The calculations account for variable inductances affected by slotting and eccentricity. The calculations were followed by Fourier analysis of the stator currents in steady state operation. The paper includes stator current spectrums affected by different degrees of static eccentricity to demonstrate the effect of static eccentricity on the stator current spectrum and to predict the harmonics related to this ailment. The motor under investigation represents a special example because its stator current spectrum includes more than one slot harmonic that is, supposedly, due to the unique configuration of the stator winding and rather high number of pole pairs (p=5). Zooms of the current spectrums, around the 50 Hz fundamental harmonic as well as of each slot harmonic zone, are included. In addition the paper includes the stator current spectrum that referred to the real measured currents. 2015-12-01T00:00:00Z http://dspace-su.server.ly:8080/xmlui/handle/123456789/1543 on some Techniques of Treating Weakly Singular Integrals Hanya A. M. Ben Hamdin The weak singularity issue arises in the boundary integral equations either directly or as a result of reducing the hypersingularity to at worst weak singularity by using some regularization formulae. Here we show some analytic and numerical techniques to deal with the weak singularity phenomenon of the boundary integral equations. These powerful techniques include the logarithmic Gaussian quadrature, subtraction of singularity and coordinate transformations that are formulated in such a way that the singularity is removed. 2015-12-01T00:00:00Z http://dspace-su.server.ly:8080/xmlui/handle/123456789/1540 Microstructure Evolution of A356 Alloy Under Ultrasonic Vibration Abdalfattah A. Khalil; Maftah H. Alkathafi; Mohamed A.Waly Grain refinement and modification of eutectic silicon in Al-Si alloy are considered as important task resulting from solidification process. Two different approaches to grain refinement by solidification process have been pursued chemically stimulated and physically induced. The chemical route depends primarily on addition of grain refiner, while the physical relies mainly on the use of external field, such as ultrasonic vibration, which is the subject of this research work. Ultrasonic vibration was used to modify the microstructure of A356 alloy. The effect of ultrasonic vibration on the solidification of the A356 alloy was investigated and the obtained samples were characterized by optical microscopy, scanning electron microscopy (SEM) and mechanical properties as well. The results showed that both the primary aluminium and eutectic silicon were significantly refined; the dendritic primary aluminium became small polygonal and globular in some cases, in addition the plate-like or big spherical eutectic silicon turned into rod-like and small spheres during the solidification process under ultrasonic vibration. The mechanism of the microstructure evolution under ultrasonic vibration was also preliminarily discussed. 2015-12-01T00:00:00Z