Showing papers by "Chittagong University of Engineering & Technology published in 2010"

Impact of large-scale PV penetration on power system oscillatory stability

Abstract: This paper presents the impact of large-scale photovoltaic (PV) generation on power system oscillatory instability. Two models of PV generation systems, namely detailed dynamic and simplified models, have been studied in IEEE-14 bus test system typically used for power system oscillatory instability studies. Influence of radiation pattern, and size and location of PV generating system on the power system stability issue is thoroughly investigated. In PV generation penetration, two scenarios, namely concentrated and scattered are examined. Simulation shows that the increased penetration of PV system enhances power system oscillatory stability.

Prospects of Back Surface Field Effect in Ultra-Thin High-Efficiency CdS/CdTe Solar Cells from Numerical Modeling

Abstract: Polycrystalline CdTe shows greater promises for the development of cost-effective, efficient, and reliable thin film solar cells. Results of numerical analysis using AMPS-1D simulator in exploring the possibility of ultrathin, high efficiency, and stable CdS/CdTe cells are presented. The conventional baseline case structure of CdS/CdTe cell has been explored with reduced CdTe absorber and CdS window layer thickness, where 1 μm thin CdTe and 50 nm CdS layers showed reasonable efficiencies over 15%. The viability of 1 μm CdTe absorber layer together with possible back surface field (BSF) layers to reduce minority carrier recombination loss at the back contact in ultra thin CdS/CdTe cells was investigated. Higher bandgap material like ZnTe and low bandgap materials like Sb2Te3 and As2Te3 as BSF were inserted to reduce the holes barrier height in the proposed ultra thin CdS/CdTe cells. The proposed structure of SnO2/Zn2SnO4/CdS/CdTe/As2Te3/Cu showed the highest conversion efficiency of 18.6% (Voc = 0.92 V, Jsc = 24.97 mA/cm2, and FF = 0.81). However, other proposed structures such as SnO2/Zn2SnO4/CdS/CdTe/Sb2Te3/Mo and SnO2/Zn2SnO4/CdS/CdTe/ZnTe/Al have also shown better stability at higher operating temperatures with acceptable efficiencies. Moreover, it was found that the cells normalized efficiency linearly decreased with the increased operating temperature with relatively lower gradient, which eventually indicates better stability of the proposed ultra thin CdS/CdTe cells.

Maximum power point tracking of photovoltaic arrays in Matlab using fuzzy logic controller

Abstract: A generalized photovoltaic array simulation model in Matlab/Simulink environment is developed and presented in this paper. The model includes PV module and array for easy use on simulation platform. The proposed model is designed with a user-friendly icon and a dialog box like Simulink block libraries. Considering the effect of solar irradiance and temperature changes, the output current and voltage of PV modules are simulated and optimized using this model. A fuzzy logic based maximum power point tracker is also developed using the presented model in Matlab/Simulink. The maximum power point tracker is tested in changing environment of irradiance and/or temperature. It can successfully track the maximum power point more accurately and quicker than conventional perturb and observe based controller in these situations. The overall test results validate the efficiency of the model as well as the fuzzy controller which can be used in related research works.

Strength Behavior of Mortar Using Fly Ash as Partial Replacement of Cement

Abstract: This paper reports the results of an experimental investigation carried out to study the effects of fly ash on strength development of mortar and the optimum use of fly ash in mortar. Cement was partially replaced with six percentages (10%, 20%, 30%, 40%, 50% and 60%) of class F fly ash by weight. Ordinary Portland cement (OPC) mortar was also prepared as reference mortar. Compressive as well as tensile strengths of the mortar specimens were determined at 3, 7, 14, 28, 60 and 90 days. Test results show that strength increases with the increase of fly ash up to an optimum value, beyond which, strength values start decreasing with further addition of fly ash. Among the six fly ash mortars, the optimum amount of cement replacement in mortar is about 40%, which provides 14% higher compressive strength and 8% higher tensile strength as compared to OPC mortar.

Effect of Sea Salts on Structural Concrete in a Tidal Environment

Abstract: Structural concrete exposed to the tidal/splash zone of marine environments is always subjected to ambient external, as well as internal, action of seawater over its entire lifespan. The environmental loading causes maximum damage to structural concrete in the tidal/splash zone of marine environments where it experiences the concentrated effect of salt ions found in seawater in presence of atmospheric oxygen, carbon dioxide and other harmful gases. The gradual penetration of sea salt ions and the formation of expansive/leachable compounds leads to cracking, spalling and even structural distress. This paper presents a part of a durability study on the effect of sea salts on structural concrete exposed to simulated tidal/splash zone marine conditions over a period of one year. The concrete specimens cast from two different grades of concrete were exposed to seawater of different concentration under submerged, alternate wetting-drying and atmospheric state of exposure in a controlled humidity and temperature environment. Using accelerated test techniques, the deteriorative effects were measured by studying visual appearance, weight and volume change, compressive strength, permeability and stress-strain characteristics, and x-ray diffraction patterns of salt-attacked concrete specimens. The test data provide useful information regarding the durability of structural concrete exposed to the tidal/splash zone of marine environments.

Modeling and performance analysis of a generalized photovoltaic array in Matlab

Abstract: A generalized photovoltaic array simulation model in Matlab/Simulink environment is developed and presented in this paper The model includes PV module and array for easy use on simulation platform The proposed model is designed with a user-friendly icon and a dialog box like Simulink block libraries This makes the generalized PV model easily simulated and analyzed even with a maximum power point tracker Considering the effect of solar irradiance and temperature change, the output current and voltage of PV modules are simulated and optimized using the proposed model The model was tested using a directly coupled dc load as well as an ac load via an inverter The test result validates the model which can be used in related research works

Installation of a Solid-Waste fuelled Power Plant in Chittagong, Bangladesh: A feasibility study

Abstract: Global interest in renewable energy resources from organic solid wastes has increased, as there is a huge amount of energy locked in these wastes. A study on the potential of such energy resources is presented in the paper. It is estimated that a Solid-Waste fuelled Power Plant (SWFPP) of 8-MW is feasible to be installed in Chittagong City Corporation (CCC), Bangladesh. The technology and cost analysis of such a power plant is also presented in the paper.

An Efficient Audio Watermarking Algorithm in Frequency Domain for Copyright Protection

Abstract: Digital Watermarking plays an important role for copyright protection of multimedia data. This paper proposes a new watermarking system in frequency domain for copyright protection of digital audio. In our proposed watermarking system, the original audio is segmented into non-overlapping frames. Watermarks are then embedded into the selected prominent peaks in the magnitude spectrum of each frame. Watermarks are extracted by performing the inverse operation of watermark embedding process. Simulation results indicate that the proposed watermarking system is highly robust against various kinds of attacks such as noise addition, cropping, re-sampling, re-quantization, MP3 compression, and low-pass filtering. Our proposed watermarking system outperforms Cox’s method in terms of imperceptibility, while keeping comparable robustness with the Cox’s method. Our proposed system achieves SNR (signal-to-noise ratio) values ranging from 20 dB to 28 dB, in contrast to Cox’s method which achieves SNR values ranging from only 14 dB to 23 dB.

Shared key vulnerability in IEEE 802.16e: Analysis & solution

Abstract: As a promising broadband wireless technology, WiMAX has many salient advantages over such as: high data rates, quality of service, scalability, security and mobility. Many sophisticated authentication and encryption techniques have been embedded into WiMAX but it still facing a lot of challenging situations. This paper shows different security vulnerabilities found in IEEE 802.16e and gives possible solutions to eliminate them. These vulnerabilities are the possibilities to forge key messages in Multi- and Broadcast operation, some unauthenticated messages which are susceptible to forgery and the unencrypted management communication which reveals important management information. We modify DH key exchange protocol to fit it into mobile WiMAX network as well as eliminate existing weakness in original DH key exchange protocol.

A modified New Reno for performance enhancement of TCP in wireless network

Abstract: Transmission Control Protocol (TCP) is the dominant transport protocol in the Internet and supports many of the most popular Internet applications, such as the World Wide Web (www), file transfer and e-mail. TCP assumes congestion which is the primary cause of packet loss and uses congestion control mechanisms such as Tahoe, Reno and New Reno to overcome this congestion in wireless network. These TCP variants take longer time to detect and recover packet loss. In order to improve retransmission scheme, we propose a modified version of New Reno that shows better performance than previous TCP variants because of utilizing faster retransmission scheme as well as transferring more packets to the destination.

Facial Features Approximation for Expression Detection in Human-Robot Interface

Abstract: This paper presents a facial expression recognition system employing Bezier curves approximation technique. The system is based on facial features extraction using the knowledge of the face geometry and approximated by 3rd order Bezier curves representing the relationship between the motion of features and changes of expressions. For face detection, color segmentation based on the novel idea of fuzzy classification has been employed that manipulates ambiguity in colors. Experimental results demonstrate that this method can recognize the facial expressions with an accuracy of more than 90% in all cases. Finally the system has been implemented using a manipulator robot and issuing facial expression commands.

Forced convection film condensation on a horizontal tube with variable properties

Abstract: The paper presents the results of numerical calculations for filmwise condensation of downward flowing pure saturated steam on a horizontal tube. A tube of 19.05 mm diameter was used. Steam approach conditions used were 5000 N/m 2 (T sat = 32.9 o C) pressure and velocity 5 – 100 m/s. Tube wall temperatures were considered to be constant at 22.9 o C and 30.9 o C, giving condensate subcooling D T = 10 K and 2 K respectively. Earlier theoretical studies omitted the variations of physical properties with pressure arising from flow of vapor over the tube surface. The present work takes into account these property variations. The velocity and pressure distributions were taken from the potential flow theory. At low condensate subcooling, D T = 2 K, and high steam velocities, significant reduction of average heat transfer coefficient was predicted when property variations were taken into account, compared to constant property values. The mean heat flux predicted considering the variation of properties was up to 9 % and 42 % less than that obtained for D T = 10 K and 2 K respectively. Keywords: Laminar filmwise condensation; horizontal tube; boundary layer separation; numerical. DOI: 10.3329/jme.v40i2.5347 Journal of Mechanical Engineering , Vol. ME 40, No. 2, December 2009 79-89

Effects of carrier gas flow-rate and oxygen admixture ratio on particle parameters in Ar-O 2 plasma

Abstract: Taking into account the strong plasma-particle interactions and particle loading effects, a model of plasma-particle interaction of argon-oxygen plasma has been developed for the numerical predict the particle temperature, velocity, trajectory and plasma temperature isotherm during the in-flight treatment. In this model the conservative equations solves the conservative equations to predict the plasma trajectories under local thermal equilibrium condition. It is found that the carrier gas flow-rate strongly affects the particle temperature and the admixture ratio of oxygen to argon affects the plasma temperature isotherm as well as the particle temperature.

Quantification of errors in the wilson plot applied to condensation on the outside of tubes

Abstract: In condensation over horizontal tubes where the wall temperature is not measured directly, the Wilson plot is used to determine the cooling side heat transfer coefficient. Conventionally, the variation in Nusselt number, Nu, with condensate side temperature drop, D T s , which accompanies change of cooling side flowrate, is assumed to be Nu µ 1/ D T s n with n = 0.25. This is the free convention condensation value. In this paper a technique is devised, not only to check the accuracy of this assumption in the usual vapor side cross flow situation, but also to determine the effect on this accuracy of allowing the index n to vary. In a case study the best agreement between D T s assumed and the value obtained using the cooling side heat transfer coefficient which resulted from the Wilson plot, occurred at n = 0.21. Based on the random errors in the measured data, a linear regression taking into account the errors in both Wilson plot coordinates gave the cooling side heat transfer coefficient and its uncertainty . Keywords: Heat transfer; condensation; Wilson plots. DOI: 10.3329/jme.v41i1.5360 Journal of Mechanical Engineering , Vol. ME 41, No. 1, June 2010 31-41

An agent-based cooperative communication method in wireless sensor network for port logistics

Abstract: Cooperative communication has been considered as a promising method for benefiting the advantages from MIMO (multiple-input multiple-output) system for single antenna mobiles in the wireless network, and many important milestones in this area have been achieved, leading to a flurry of research activity. Especially, cooperative communication in wireless sensor networks (WSNs) has gained so much interest due to the limitations of WSNs. This paper proposes a new cooperative communication method for WSNs in port logistics according to the observation of real application in port. In our proposed method, we use some fixed agents to help the sensor nodes to gain more efficient communication in the network. The simulation results and analysis show that our method achieves a good performance in enhancing the transmission and energy efficiency, resulting in improvement of the communication performance of the whole network.

A safe system with safe logistics support for Chittagong Port

Abstract: This paper presents a prototype implementation of an intelligent system called safe system that monitors container security in the port logistics. Logistics supports in the port require safe container status. The main focus of our contribution is to design a system that supports RFID (Radio Frequency Identification) Readers of all types (such as Reader Protocol complaint and vendor provided Readers), real time monitoring of sensing information and notify management about the status of the container in harbor logistics.

Parallel Data Transmission: A Proposed Multilayered Reference Model

Abstract: Data transmission process between host to host in the computer network follows a basic system namely OSI reference model In this model data processing starts at the application layer, breaks the data into segments at the transport layer and processing ends at the physical layer Afterwards it transfers segmented data between different layers, bit wise conversion taking place at the physical layer through the medium In this paper a new parallel data transmission process has been proposed In this research all segmented data broken in the transport layer at the same time, transfer through the medium There is an interrelationship between layers in the proposed model Moreover this system has both way data transmission capability Layers can inherit information from upper or lower section This leads the system to more dynamic that is evolutionary To support this type of data transmission process, a new reference model proposed in this research And thus the system model works faster and more error free than the existing data transmission system

An efficient algorithm for finding the control point of 3 rd order Bezier curve

Abstract: This paper represents a modified algorithm to recover the control points of 3rd order Bezier curves more efficiently. It uses the two stage approximation learning algorithm with some modifications. In this regards, at 1st stage we modify the height (H) where we assume approximate 2nd and 3rd control points and at 2nd stage we modify the step size (δ) which moves the assumed control points towards the accurate control points. Experimental results demonstrate that our proposed method minimize the error level and reduce computation time for recovering the control points than the previous one. Our computer simulation proves the effectiveness of our proposed method.

Robust Audio Watermarking Scheme Based on Deterministic Plus Stochastic Model

Abstract: Digital watermarking has been widely used for protecting digital contents from unauthorized duplication. This paper proposes a new watermarking scheme based on spectral modeling synthesis (SMS) for copyright protection of digital contents. SMS defines a sound as a combination of deterministic events plus a stochastic component that makes it possible for a synthesized sound to attain all of the perceptual characteristics of the original sound. In our proposed scheme, watermarks are embedded into the highest prominent peak of the magnitude spectrum of each non-overlapping frame in peak trajectories. Simulation results indicate that the proposed watermarking scheme is highly robust against various kinds of attacks such as noise addition, cropping, re-sampling, re-quantization, and MP3 compression and achieves similarity values ranging from 17 to 22. In addition, our proposed scheme achieves signal-to-noise ratio (SNR) values ranging from 29 dB to 30 dB.

A better way for finding the optimal number of nodes in a distributed database management system

Abstract: Distributed Database Management System (DDBMS) is one of the prime concerns in distributed computing. The driving force of development of DDBMS is the demand of the applications that need to query very large databases (order of terabytes). Traditional Client- Server database systems are too slower to handle such applications. This paper presents a better way to find the optimal number of nodes in a distributed database management systems. Keywords: DDBMS, Data Fragmentation, Linear Search, RMI. DOI: 10.3329/diujst.v4i2.4362 Daffodil International University Journal of Science and Technology Vol.4(2) 2009 pp.19-22