UET Peshawar Publications Site (University of Engineering and Technology, Peshawar)
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MULTIOBJECTIVE PSSs DESIGN FOR DAMPING INTRA-AREA OSCILLATIONS IN MULTI-MACHINES POWER SYSTEM USING HIERARCHICAL MICRO GA
No full textIn recent years, the occurrence of Low Frequency Oscillations (LFOs) has increased due lo the growth in size and complexity of power systems. This has strong impact on overall system and can deteriorate power system angular stability. The classical and cost effective way of preventing low-frequency oscillations in power system is to use power system stabilizers (PSSs). These controllers have been traditionally designed using classical theory such as eigenvalue/eigenvector analyses, root locus, etc., and are made of lead-lag networks. However, because the parameters of the controllers are fixed they cannot provide adequate damping over a wide range of operating conditions. The objective of this paper is to develop cost-effective control strategy that maintain the lead-lag structure of existing PSSs while optimizing the robust performance of the controller to cope with various uncertainties in the system and varying operating conditions.In this paper a method for selecting and tuning multiple power system damping controllers simultaneously by genetic algorithms (GA s) has presented. The performance of the control system is considered for different operating conditions to ensure robustness of the controllers. Robust multi objective design of the PSSs is achieved that ensures system stability by shifting the poles to the desired place in the left half s-plane
LS DYNA AS A VALID TOOL FOR ANALYZING STRESS WAVE PROPAGATION UNDER IMPACT LOADING
No full textHopkinson Fracture bar was successfully modeled in ANSYS — LS DYNA. The results showed very good conformity with stress wave theory used for analyzing impact experiments. Ramberg-Osgood constitutive model was successfully employed to simulate high strain rate deformation. The materials constants used in Ramberg-Osgood for the commercial purity aluminum and 440 WGA steel were determined by comparison with experiments. The results showed mesh independence. The current study validates LS DYNA as a tool to analyze dynamic experiments using stress wave theory
CAPACITIVE TRANSDUCER CIRCUIT FOR LIQUID LEVEL MEASUREMENT
No full textThis paper presents a capacitance measuring circuit used for the measurement of liquid levels in a container and its corresponding results. The transfer function of the circuit is derived to confirm that the measured parameter can be directly proportional to the liquid level while keeping other values constant. Experimental results show that under similar conditions, changes in capacitance produce identical changes ¡n an output voltage which, when plotted against the changes in the liquid level, show up a good level of linearity. Furthermore, results are obtained with different liquids which are clearly justifying the accuracy of circuit and the apparatus used
PERFORMANCE OF MODIFIED UNCOATED TUNGSTEN CARBIDE INSERT
No full textIn high speed and high production machining, cemented carbide tools are widely used for its superior characteristics. These superior characteristics of cemented carbide are mainly governed by the grain size of the tungsten carbide particles and the cobalt content. The tool life and machining performance can be controlled by the composition of the cemented carbide tool alloy. In this research, machining performance of uncoated cemented carbide inserts are examined experimentally by changing the alloying compositions of the inserts. For this purpose a new insert of cemented carbide is fabricated by modifying the traditional existing compositions and grain size of tungsten carbide (WC), while the other process parameters are kept within the standard value. To compare the performance of the new insert with the existing traditional insert, machining on steel is performed under same cutting condition. Tool wear, surface finish, chip-tool inertface temperature and tool life are measured and compared with the existing tool. It is experimentally found that surface finish of machined part is improved whereas tool wear and temperature generation are reduced for the newly fabricated insert
STRENGTH PREDICTION OF STEEL TUBULAR SQUARE COLUMNS IN-FILLED WITH CONCRETE
No full textThe behaviour of concrete filled steel tubular (CFST) square column sections with various concrete (partial replacement of fine aggregate by fly-ash and quarry dust and coarse aggregate by granite and construction & demolition debris) strength under axial load is presented. The effects of steel tube size, length and the confinement of concrete are examined. Measured column strengths are compared with the values predicted by Eurocode 4, Australian Standards and American Codes. 18 specimens were tested with strength of concrete as 20 MPa, L/D ratio varies from 4.16 to 12.5 and a D/t ratio of 22.5. The columns were 72.0 mm in side, 3.2 mm in thick and are 300, 600 & 900 mm in length. All the three codes and modified ACI/AS predicted lower values when compare to experimental results. Hence ACl/AS equation is proposed by multi plying factor ‘k’ to predict good results for columns of L/D < 12 In this study k factor for varies L/D ratio from 4 to 12 are suggested. Modified ACI/AS gives the best estimation for CFST sections with 900 mm column length
AIRCRAFT FAULT IDENTIFICATION AND DIAGNOSIS USING AN EXPERT SYSTEM: A CASE STUDY
No full textArtificial intelligence (Al) technology is widely suggested for systematic diagnosis of faults where the amount of well-defined diagnosis knowledge ¡s vast and the sequence of steps required to identify the fault is very long. This paper addresses the practical use of Expert System (ES) for aircraft fault identification and diagnosis. A prototype Expert System has been developed using Microsoft Windows® based K-Vision® software, a freely available expert system development tool and run on a PC. The heart of the ES i.e., the knowledge base has been developed from interviewing the experts, existing aircraft manuals and maintenance history. It has been demonstrated that expert systems can be employed effectively for aircraft fault identification and diagnosis as well as for any other problem area. The result of this development is expected to introduce a systematic and intelligent method in aircraft fault identification and diagnosis and also act as a tutor for inexperienced aircraft technicians and engineers. The paper gives brief theory of the Expert Systems and then a demonstration of the software is presented
RELIABILITY ANALYSIS OF ECCENTRICALLY LOADED WELDED CONNECTIONS IN DIRECT SHEAR AND TENSION: APPROXIMATE PROCEDURE
No full textReliability analysis of eccentrically welded connections fabricated from grade S2 75 steel plates, in direct shear and tension using approximate method of analysis in accordance with BS5950’ was carried using First Order Reliability Method (FORM). Design variables such as load eccentricity, ratio of breadth-to-depth of weld, weld strength and throat thickness of weld were varied at varying values of design eccentric loads. Based on the results presented, failure of the four-sided welded connections is more sensitive to variation in the strength of weld and would occur at lower weld strengths. On the other hand, in three-sided welded connections, failure occurs as a result of insufficient breadth-to depth ratio. It was also shown among other findings that, the target safety indices of four-sided and three-sided welded connections are 2.872 and 3.005 respectively. The design of the two types of connections considering the BS5950’ design criteria are satisfactory and economical2. Again, the four-sided connection is in practice loaded with higher eccentric loads because of its stability, but, will however, be unsafe at very high loads. The BS5 950’ design criteria of eccentrically loaded welded connections in direct shear and tension using approximate design procedure is satisfactory
REVIEW AND IMPLEMENTATION OF A NOVEL METHODOLOGY FOR AUTOMATED DESIGN OF MECHATRONIC SYSTEMS
No full textModern dynamic engineering systems can be characterized as mechatronic systems. The multi-domain nature of a mechatronic system makes it difficult to model using a single modeling technique over the whole system as varying sets of system variables are required. Bond-Graphs offer an advanced unified and object oriented modeling and simulation technique. They are domain independent allowing straightforward and efficient model composition, classification and analysis. Bond-Graph model of the mechatronic system can be directly simulated on a digital computer using simulation softwares like 20-Sim and Modelica graphically or manipulated mathematically to yield state equations using a simplified set of power and energy variables. The simulation scheme can be augmented to synthesize designs for mechatronic systems using genetic programming as a tool for open-ended search. This research paper presents results of simulated experiments that combine Bond-Graph modeling and simulation with genetic programming for automated design of a simple mechatronic system. A brief introduction to the methodology and review of associated concepts is also included
SUPPLEMENTAL IRRIGATION TO IMPROVE WHEAT PRODUCTION AND WATER USE EFFICIENCY UNDER RAINFED FARMING CONDITIONS
No full text
The stochastic behaviors of rainfall pose serious limitations for sustained and profitable crop production in rainfed areas; farmers hesitate to apply fertilizers when they are not sure about rainfall. In view of these limitations a research study was conducted for three years (2003-2006) at field station of Water Resources Research Institute (WRRI), National Agricultural Research Centre(NARC), Islamabad to examine the effects of supplemental irrigation (SI) on wheat production and water use efficiency (WUE). Irrigation treatments employed under the experiment were: i) Rainfed without irrigation and fertilizer application (I0); ii) SI of 25 mm was applied to non-fertilizer field at 75% management allowed deficit (MAD) (I1); iii) Rainfed with fertilizer application at sowing time (I2); and iv) SI of 25mm was applied at 75% MAD and at the time of fertilizer application as top dressing (I3).Supplemental irrigation increased the crop yield during the years 2003-2006 under both fertilizer and non-fertilizer conditions. Increased in grain yield under non-fertilizer conditions (I1) ranges between 770-980 kg/ha, which is 27 to 48% higher than the rainfed yield (I0). Supplemental irrigation and split application of fertilizer (treatment I3) increased the grain yield within the range of 1000-1350 kg/ha, which is 27-49% higher than yield under treatment I2. Whereas, due to synergetic effect of supplemental irrigation and fertilizer application, increased in grain yield ranges between 1550-2030 kg/ha, which is 49% to 100% higher than the rainfed and non-fertilizer field.WUE was calculated for rain (WUEr), for total water (grass: previous soil water storage + rain + irrigation) (WUEg), for SI water only (WUEsi) and for synergetic effect (SI water + fertilizer application) (WUEsis). Water use efficiencies namely the WUEr, WUEg and WUEsi, during the period of three years under non-fertilizer conditions ranges between 6.2-7.1, 7.9-8.5 and 19.6-30.8 kg/ha/mm of water respectively. The water use efficiencies WUEr, WUEg and WUEsi, under fertilizer conditions ranges between 7.0-8.7, 8.5-11.1 and 26.8-40 kg/ha/mm of water respectively. Whereas, the WUEsis was 40.2, 62.0 and 40.6 kg/ha/mm of water during the year 2003-04, 2004-05 and 2005-06 respectively. Supplemental irrigation increased both the wheat production and water use efficiency by supplying irrigation water at critical moisture stress and improving level of input.
 
A NEW APPROACH TOWARDS DURABILITY DESIGN OF CONCRETE STRUCTURES
No full textA method of assessing durable life of concrete structures is presented. The durable life is related to the Durability Design Index (DDI). The DDI is obtained from the product of various durability factors which are empirically assigned to the durability requirements of the most commonly used codes of practice like ACI, BS and JCI The factors have been grouped into four categories; the durability loading, compliance to standards, protective provisions and degrees of certainty. The durability loading factors are made dependant upon aggressiveness of environment, magnitudes of displacements and deformations, reinforcement detailing and concrete cover factors. The compliance to standards factors are based upon concrete strength, quality of concrete composition, quality of reinforcement detailing and construction methodology. The protective provision factors are classified as casting stage, finishing stage and service stage protective provision factors. The degree of certainty factors have been related to the level of skill of the design and construction teams. Three case studies have been presented and the results of these case studies agreed very closely to the prediction of the proposed method