Mehran University Research Journal of Engineering and Technology

6

Authors: Ursani A.A., Shah W., Shah S.A.A.

The texture descriptors derived from 1-D DFT (Discrete Fourier Transform) of the pixel values of a local neighbourhood have been shown to perform better than the methods based on wavelets for image retrieval and recognition. These DFT-based texture descriptors were extracted from rectangular or circular neighbourhoods. This paper compares the texture descriptors extracted from rectangular and the circular neighbourhoods previously proposed in the literature. A database of images is constructed from Brodatz album and the texture descriptors extracted from the two types of neighbourhoods are compared for texture retrieval. This paper shows that extracting DFT-based features from circular neighbourhood is almost thrice as expensive as extracting the same from the rectangular neighbourhood. The results of image retrieval on a large image database show that the descriptor extracted from rectangular neighbourhoods performs better than the same extracted from the circular neighbourhoods.

6

Authors: Malik Z.A., Tanwari A., Sheikh H.R.

A study was carried out to investigate the effects of plain and 3/1 twill weave designs on the tensile strength of polyester-cotton blended fabrics. For this purpose five fabric samples, each of plain and twill designs, were made on projectile weaving machine from 15 tex polyester-cotton (52:48%) yarn. The fabric count was increased from 80 (40+40) to 160 (80+80) with equal increment of 10 threads per 25mm both in warp and weft directions to obtained fabrics of different weights. After enzymatic desizing, tensile strength of fabric samples was determined as per standard test method. Comparison of test results shows that plain fabric samples have considerable high tensile strength as compared to twill fabric samples at the same fabric counts.

8

Authors: Larik A.S., Mahar M.A., Shaikh A.R.

AC voltage controllers are used to vary the output ac voltage from a fixed ac input source. They are also commonly called ac voltage regulators or ac choppers. The output voltage is either controlled by PAC (Phase Angle Control) method or on-off control method. Due to various advantages of ac voltage controllers, such as high efficiency, simplicity, low cost and ability to control large amount of power they efficiently control the speed of ac motors, light dimming and industrial heating, etc. These converters are variable structure systems and generate harmonics during the operation which will affect the power quality when connected to system network. During the last couple of years, a number of new semiconductor devices and various power electronic converters has been introduced. Accordingly the subject of harmonics and its problems are of great concern to power industry and customers. In this research work, initially the simulation models of single phase unidirectional and bidirectional ac voltage controllers were developed by using MATLAB software. The harmonics of these models are investigated by simulation. In the end, the harmonics were also analyzed experimentally. The simulated as well as experimental results are presented.

8

Authors: Goraya R.A., Ahmed K., Tahir M.A.

GFRP (Glass Fiber Reinforced Polymer) rebars are frequently used as reinforcement for reinforced concrete. This concrete being a composite material resists the flexural & shear loads, if adequate bond exists between GFRP rebars and concrete & through which transfer of stresses take place between them. The bond strength of such concrete is a function of several factors. Out of these factors, surface texture of GFRP rebars is one of the most important parameters. Experimental study was carried out with data acquisition system and linear displacement transducers to determine the effect of surface texture (sand coatings on GFRP rebars) on adhesion & frictional component of the bond strength. Overall and post peak bond behavior was studied through pullout tests using strain controlled universal testing machine. The results of experimental work showed that by sand coating on GFRP rebars, bond strength increased for both large and small diameter rebars. Furthermore for smaller diameter rebars, the effect of sand coating was more pronounced as compared to medium & larger diameter rebars. The sand coating improved the friction between GFRP rebars and the surrounded concrete. Moreover, after failure of chemical adhesion due to slip, friction between broken sand particles and rough surface of GFRP rebars provided further resistance to slip which consequently improved the bond strength.

10

Authors: Umrani A.W., Umrani F.A., Ursani A.A.

A novel beamforming algorithm based on conjugate gradient methods is described and its performance is computed in terms of bit error rate for practical CDMA 2000 communication systems. The proposed technique attempts to maximize signal-to-noise plus interference of the received signal, and is based on solving the eigenvalue problem where the optimization of the weight vector is done using the pilot channel. The performance is simulated for practical CDMA 2000 1X communications systems in wireless propagation environments with high angle spread. The performance of the proposed beamforming algorithm is also compared with existing beamforming algorithms. Simulation results show that the performance of the proposed algorithm is more robust to higher angle spread.

12

Authors: Memon R.A., Tunio A.H., Lal K.

The results obtained from RNG (Re-Normalization Group) version of k-? turbulence model are reported in this study. The model is adopted to elucidate the impact of different building aspect ratios (i.e., ratio of building-height-to-street-canyon-width) and solar heating on temperatures in street canyon. The validation of Navier-Stokes and energy transport equations showed that the model prediction for air-temperature and ambient wind provides reasonable accuracy. The model was applied on AR (Aspect Ratios) one to eight and surface temperature difference (??s-a) of 2 -8. Notably, air-temperatures were higher in high AR street canyons in particular on the leeward side of the street canyon. Further investigation showed that the difference between the air-temperature of high and low AR street canyons ( AR) was positive and high with higher ??s-a. Conversely, the AR become negative and low gradually with lower values of ??s-a. These results could be very beneficial for the city and regional planners, civil engineers and HVAC experts who design street canyons and strive for human thermal comfort with minimum possible energy requirements.

14

Authors: Jokhio M.H., Panhwar M.I., Unar M.A.

ANN (Artificial Neural Networks) modeling methodology was adopted for predicting mechanical properties of aluminum cast composite materials. For this purpose aluminum alloy were developed using conventional foundry method. The composite materials have complex nature which posses the nonlinear relationship among heat treatment, processing parameters, and composition and affects their mechanical properties. These nonlinear relation ships with properties can more efficiently be modeled by ANNs. Neural networks modeling needs sufficient data base consisting of mechanical properties, chemical composition and processing parameters. Such data base is not available for modeling. Therefore, a large range of experimental work was carried out for the development of aluminum composite materials. Alloys containing Cu, Mg and Zn as matrix were reinforced with 1- 15% Al2O3 particles using stir casting method. Alloys composites were cast in a metal mold. More than eighty standard samples were prepared for tensile tests. Sixty samples were given solution treatments at 580oC for half an hour and tempered at 120oC for 24 hours. The samples were characterized to investigate mechanical properties using Scanning Electron Microscope, X-Ray Spectrometer, Optical Metallurgical Microscope, Vickers Hardness, Universal Testing Machine and Abrasive Wear Testing Machine. A MLP (Multilayer Perceptron) feedforward was developed and used for modeling purpose. Training, testing and validation of the model were carried out using back propagation learning algorithm. The modeling results show that an architecture of 14 inputs with 9 hidden neurons and 4 outputs which includes the tensile strength, elongation, hardness and abrasive wear resistance gives reasonably accurate results with an error within the range of 2-7 % in training, testing and validation.

16

Authors: Tunio A.H., Memon H.R., Aziz S.

Historical experimental work on the combustion oil recovery processes consists of both laboratory and field studies. Although field experiments are the ultimate test of any oil recovery process, they are costly, time consuming and difficult to analyze quantitatively. Laboratory CC (Combustion Cell) experiments are cost effective and less time consuming, but are subject to scaling and interpretation challenges. Experimental set up has been developed to understand air injection process for improving oil recovery from light oil reservoirs taking into account the sand pack petro physical and fluid properties. Some important design problems; operational criteria and considerations important to interpretation of results are pointed out. To replicate subsurface reservoir conditions or pressure and temperature, experiments up to 6895 KPa, at non-isothermal conditions with 5oC/min ramp-up are performed on unconsolidated cores with reservoir oil samples. Correlations were obtained for low temperature oxidation rate of oil, the fuel deposition rate and the rate of burning fuel as a fuel concentration. Various parameters such as (sand pack, pressure, oil saturation and flow rate/air flux) were changed to investigate their impact on reaction and chemical nature of the fuel burned. To determine the importance of distribution and pyrolysis on these reactions, the hydrogen-carbon ratio and m-ratio was calculated. For further confirmation Arrhenius graphs were drawn by assuming 1.0 order of reaction with carbon concentration which is also confirmed.This research will contribute to the overall understanding of air injection process;help to determine the most appropriate