Bailey C.G.,University of Manchester |
Yaqub M.,University of Engineering & Technology, Taxila
Composite Structures | Year: 2012
An experimental study was carried out to investigate the seismic performance of post-heated circular reinforced concrete columns wrapped with glass or carbon fibre reinforced polymer jackets. Eight shear critical reinforced circular columns with a shear span-to-depth ratio of 2.5 were tested under a combined constant axial and cyclic lateral displacement history, simulating earthquake loading. The columns were tested in three groups, unheated, post-heated and post-heated repaired with either glass fibre reinforced polymer (GFRP) or carbon fibre reinforced polymer (CFRP). In terms of seismic performance the test results indicated that using GFRP or CFRP jackets significantly increased the shear capacity, ductility and energy dissipation of the post-heated damaged columns. However, the GFRP or CFRP did not increase the stiffness of the post-heated damaged columns. It was found that the unheated and post-heated damaged columns failed in a brittle shear mode while the mode of failure of posted-heated columns repaired with GFRP or CFRP was successfully shifted from a shear to a ductile flexural failure. © 2011 Elsevier Ltd.
Yaqub M.,University of Engineering & Technology, Taxila |
Bailey C.G.,University of Manchester
Construction and Building Materials | Year: 2012
This paper describes the results of an experimental study carried out to investigate the seismic performance of post-heated reinforced concrete square columns repaired with unidirectional glass or carbon fibre reinforced polymers (GFRPs or CFRPs). The test specimens were categorized into three groups; (a) un-heated, (b) post-heated and (c) post-heated columns repaired with GFRP or CFRP jackets. Each group consisted of two columns with a shear-span-to-depth ratio of 2.5 tested under similar conditions comprising a constant axial and a lateral cyclic load simulating earthquake loading. The main variables investigated in this experimental study were the effect of heat damaged columns, the type of fibres used for repair, the orientation of the main fibres and the peak drift ratios achieved. The seismic performance of the GFRP or CFRP wrapped post-heated columns were compared to the reference un-heated and post-heated columns through the hysteretic response, shear resistance, lateral strength, ductility, energy dissipation and stiffness degradation. The test results showed that wrapping of columns with a single layer of GFRP or CFRP notably enhanced the shear capacity, ductility, energy dissipation ability and slowed the rate of strength and stiffness degradation. It was shown that the post-heated columns regained the lateral strength up to the original level of un-heated columns wrapped with a single layer of GFRP or CFRP. However, it was also shown that the post-heated columns wrapped with a single layer of GFRP or CFRP did not restore the repaired post-heated column to the original level of stiffness of the un-heated columns. Additionally, the un-heated and post-heated columns failed in shear while the governing failure mechanism of the GFRP or CFRP wrapped post-heated columns was successfully shifted from column shear to flexural failure. © 2012 Elsevier Ltd. All rights reserved.
Choudhry M.A.,University of Engineering & Technology, Taxila |
Khan H.,University of Engineering & Technology, Taxila
Energy | Year: 2010
To provide electric utility service of desired quality at the lowest possible cost, voltage drop and power loss reduction is crucial for distribution network. Distribution systems with Distributed Energy Resources (DER) have shown an enormous potential for power loss and voltage drop reduction. This paper investigates existing islanding detection techniques for feeder performance and proposes a new islanding detection algorithm (NIDA) for node voltage profile improvement and power loss reduction in the distribution network.The NIDA has been validated with three case studies. It has been investigated for its capabilities to improve the feeder performance in electric distribution system. The proposed algorithm outperforms the conventional approaches, which have many limitations to detect the islanding operation. The non-uniform distribution of electric loads, unity power factor, complexities in the design of control interface and functioning of the system in multi-DER environment are the most common obstacles in implementation of existing islanding detection techniques. NIDA is capable of handling the above mentioned complexities. The simulation results show that NIDA can detect islanding formation during the fault condition. The DER(s) provide uninterruptible power supply to sensitive load in the island, maintaining the nodes voltage and the power loss within the permissible limits. © 2010 Elsevier Ltd.
Shehzad K.,University of Engineering & Technology, Taxila
IEEE Transactions on Knowledge and Data Engineering | Year: 2013
Pruning achieves the dual goal of reducing the complexity of the final hypothesis for improved comprehensibility, and improving its predictive accuracy by minimizing the overfitting due to noisy data. This paper presents a new hybrid pruning technique for rule induction, as well as an incremental postpruning technique based on a misclassification tolerance. Although both have been designed for RULES-7, the latter is also applicable to any rule induction algorithm in general. A thorough empirical evaluation reveals that the proposed techniques enable RULES-7 to outperform other state-of-the-art classification techniques. The improved classifier is also more accurate and up to two orders of magnitude faster than before. © 1989-2012 IEEE.
Khan H.,University of Engineering & Technology, Taxila |
Choudhry M.A.,University of Engineering & Technology, Taxila
International Journal of Electrical Power and Energy Systems | Year: 2010
This paper presents a new algorithm, written in C-language for Implementation of Distributed Generation (IDG) to radial distribution feeder, heavily overloaded with non-uniformly distributed load. Majority of the existing algorithms are designed for distribution feeders with uniformly distributed load, working in single DG scenario. The applicability of these algorithms is restricted because of the unity power factor and high computational work. The methodology proposed in the research paper is capable of functioning under randomly distributed load conditions with low power factor for single DG as well as multi-DG system. The algorithm is based on analytical approach and is implemented to radial distribution network, considering the worse case scenario. The analyses carried out show that the algorithm can be applied to enhance the performance of distribution system in terms of node voltage profile improvement and power loss reduction. The simulation results indicate that IDG is capable of identifying the optimal location and size of DG in any problematic distribution system effectively. The results obtained are verified and are within the international standards limits. © 2010 Elsevier Ltd.
Ghazanfar M.A.,University of Engineering & Technology, Taxila |
Prugel-Bennett A.,University of Southampton
Expert Systems with Applications | Year: 2014
Recommender systems apply data mining and machine learning techniques for filtering unseen information and can predict whether a user would like a given item. This paper focuses on gray-sheep users problem responsible for the increased error rate in collaborative filtering based recommender systems. This paper makes the following contributions: we show that (1) the presence of gray-sheep users can affect the performance - accuracy and coverage - of the collaborative filtering based algorithms, depending on the data sparsity and distribution; (2) gray-sheep users can be identified using clustering algorithms in offline fashion, where the similarity threshold to isolate these users from the rest of community can be found empirically. We propose various improved centroid selection approaches and distance measures for the K-means clustering algorithm; (3) content-based profile of gray-sheep users can be used for making accurate recommendations. We offer a hybrid recommendation algorithm to make reliable recommendations for gray-sheep users. To the best of our knowledge, this is the first attempt to propose a formal solution for gray-sheep users problem. By extensive experimental results on two different datasets (MovieLens and community of movie fans in the FilmTrust website), we showed that the proposed approach reduces the recommendation error rate for the gray-sheep users while maintaining reasonable computational performance.© 2013 Elsevier Ltd. All rights reserved.
Ali H.M.,University of Engineering & Technology, Taxila |
Briggs A.,Queen Mary, University of London
Applied Thermal Engineering | Year: 2014
Retention angle measurements on 15 rectangular pin-fin tubes are made under static conditions (without condensation) using water, ethylene glycol and R-113. Condensate retention angles found to be considerably larger than the equivalent integral-fin tubes (i.e. with the same fin height, root diameter and longitudinal pin thickness and spacing) in a range of 5%-60%. An expression for condensate retention angle on pin-fin tubes was proposed and found to agree with the measured retention angles to within 15%. © 2013 Elsevier Ltd. All rights reserved.
Ali H.M.,University of Engineering & Technology, Taxila |
Briggs A.,Queen Mary, University of London
International Journal of Heat and Mass Transfer | Year: 2015
A simple semi-empirical correlation accounting for the combined effect of gravity and surface tension has been developed for condensation on horizontal pin-fin tubes. The model divides the heat transfer surface into five regions, i.e. two types of pin flank, two types of pin root and the pin tip. Data for three fluids (i.e. steam, ethylene glycol and R113) condensing on eleven tubes with different geometries were used in a minimization process to find three empirical constants in the final expression. The model gives good overall agreement (within ±20%) with the experimental data, as well as correctly predicting the dependence of heat-transfer enhancement on the various geometric parameters and fluid types. © 2014 Elsevier Ltd. All rights reserved.
Ahmad S.,University of Engineering & Technology, Taxila
JVC/Journal of Vibration and Control | Year: 2010
Rubbing between a rotor and its casing has long been recognized as a major contributor to excessive maintenance and in general to machinery failure. During contact, the high energy of the rotor, dissipated by the frictional force, can severely damage both parts, and can lead to total destruction of the machine. The purpose of this article is to provide an overview of the state of the art on the rotor-casing contact phenomenon in rotor dynamics, describing aspects of different physical parameters such as stiffness, damping, Coulomb friction, acceleration of rotor, support structure asymmetry, thermal effects and disk flexibility etc. The intention is to summarize the results presented in literature which are beneficial for the designers of rotating machines and also a source of research inspiration for the scientists and technologists working in this field. © 2010 SAGE Publications Los Angeles.
Ahmed D.,University of Engineering & Technology, Taxila |
Ahmad A.,University of Engineering & Technology, Taxila
Journal of Physics: Conference Series | Year: 2013
Different types of generators are currently being used in wind power technology. The commonly used are induction generator (IG), doubly-fed induction generator (DFIG), electrically excited synchronous generator (EESG) and permanent magnet synchronous generator (PMSG). However, the use of PMSG is rapidly increasing because of advantages such as higher power density, better controllability and higher reliability. This paper presents an innovative design of a low-speed modular, direct-drive axial flux permanent magnet (AFPM) generator with coreless stator and rotor for a wind turbine power generation system that is developed using mathematical and analytical methods. This innovative design is implemented in MATLAB / Simulink environment using dynamic modelling techniques. The main focus of this research is to improve efficiency of the wind power generation system by investigating electromagnetic and structural features of AFPM generator during its operation in wind turbine. The design is validated by comparing its performance with standard models of existing wind power generators. The comparison results demonstrate that the proposed model for the wind power generator exhibits number of advantages such as improved efficiency with variable speed operation, higher energy yield, lighter weight and better wind power utilization. © Published under licence by IOP Publishing Ltd.