AJSE Vol 14 No 1 August 2015
Design and Evaluation of a Compact Ultra Wide Band Textile Antenna for Wearable Body Area Applications
Shahriar Hasan Shehab
American International University-Bangladesh, Bangladesh
Shahreen Hassan
American International University-Bangladesh, Bangladesh
Farhadur Arifin
American International University-Bangladesh, Bangladesh
Abstract
In this paper the design of a novel compact Ultra wide band (UWB) textile antenna is realized. The designed UWB antenna operates from the frequency range of 3 GHz to 14 GHz, covering the entire Ultra wide band frequency range of 3.1-10.6 GHz, as approved by FCC. Hybrid design technique is applied to a simplified circular patch design and finally a slotted octagonal shape is achieved that exhibits Ultra wide band characteristics. The substrate of the designed antenna is made of Fleece fabric (ɛr= 1.17) while patch and the ground plane is made of copper tape. The dimension of the substrate is 40×30 mm2. A partial ground plane with a square notch is placed at the back of the substrate. This antenna performance is also analyzed at eight different bending angles. The characteristics, low profile and compact size of the proposed antenna depicts as a potential candidate for Ultra wide band applications.
Effects of Active Region Thickness on the Performance Characteristics of InGaN Based 420 nm MQW Blue Violet Laser
Aniqa Tahsin
American International University-Bangladesh, Bangladesh
Tinni Rani Paul
American International University-Bangladesh, Bangladesh
Shakhila Afrin
American International University-Bangladesh, Bangladesh
Rinku Basak
American International University-Bangladesh, Bangladesh
Abstract
In this work, the effects of active region thickness variation on the performance characteristics of a MQW blue violet laser are discussed. For this purpose the structure is designed using In0.156Ga0.844N/Al0.07Ga0.93N. The active region thickness is varied from 27 nm to 31 nm to understand the effects of active region thickness variation on the performance characteristics of the designed laser. The laser structure with smaller active region thickness has the lower threshold current which increases the optical output power and total efficiency. The performance characteristics and their dependence to active region thickness of the blue violet laser have been investigated by using MATLAB simulation. It was found that lasers having smaller active region thickness give better performance.
Performance Evaluation of Energy Detection based Cooperative Spectrum Sensing for Cognitive Radio
Ikram Ilyas
Uttara University, Bangladesh
Niger Fatema
Australian International School-Dhaka, Bangladesh
Md. Abdur Rahman
American International University-Bangladesh, Bangladesh
Abstract
Radio frequency spectrum is a very limited resource. With the increased dependence on modern wireless devices, the management and proper utilization of the spectrum has become a major challenge. The concept of cognitive radio aims to overcome these problems by helping to achieve improved spectral management, utilization, and efficiency. To sense the unoccupied spectrum gap is one of the essential tasks of cognitive radio. There are many spectrum sensing algorithms available for cognitive radio. This paper describes Energy Detection based detection method of cooperative and non-cooperative spectrum sensing for cognitive radio. We also spoke about the basics of Cognitive Radio and developed Simulink models for the Hard Decision Fusion Method and the Soft Decision Fusion Method of the Cooperative spectrum sensing technique. We compared the performance of the OR Method and the SC Method of Energy Detection Spectrum Sensing and discussed which of the methods has a better performance based on the observed output spectrum of each method.
Design and Performance Analysis of Nano Microstrip Rectangular Patch Antenna at 0.25 THz
Mehnaj Mahbuba
American International University-Bangladesh, Bangladesh
Nafiz Ahmed Chisty
American International University-Bangladesh, Bangladesh
Abstract
To achieve the future demand of high data rates and high gain with better efficiency, two nano Microstrip patch antennas were designed with nickel and silver substrates. The operating or resonance frequency selected for the two antennas was 0.25 THz or 250 GHz. The main reason behind designing the antenna at 250 GHz is that the frequency range is completely free. The rectangular shape of the patch was selected because of the simplicity of dimension calculation. The transmission line model was taken for the analytical purpose. It is the simplest model of all other models. The values of patch width and length were calculated. The height of the antenna was taken too small for better performance. To operate the antennas at desired 250 GHz some dimensions were varied. Directivity of 16.37 dBi was found for the Nickel substrate patch antenna and 17.37 dBi directivity was found for the Silver substrate patch antenna.
Performance Analysis of MIMO Antennas Based on Compact Corner Notched Printed Rectangular Monopole Antenna for UWB Applications
Mohammad Tareq
Dhaka International University, Bangladesh
Zeenat Afroze
American International University-Bangladesh, Bangladesh
Abstract
In this paper a compact 
Multiple-Input Multiple-Output (MIMO) antenna has been proposed for ultra-wideband (UWB) applications. Proposed MIMO antenna has been designed based on a Printed Rectangular Monopole Antenna (PRMA) and two 
MIMO antennas. Proposed MIMO antenna satisfies the UWB design specifications such as reflection coefficient, transmission coefficient, group delay, correlation coefficient and radiation pattern. All of the simulations have been carried out by Computer Simulation Technology Microwave Studio (CST MWS) 2013.
Design of A Novel, Low-Profile, Elliptical Patch Super Wide Band MIMO Antenna and Performance Analysis for UWB Applications
Md. Ashif Islam Oni
World University of Bangladesh, Bangladesh
M. Tanseer Ali
American International University-Bangladesh, Bangladesh
Abstract
In this paper, A novel, low-profile, coplanar waveguide fed elliptical patch Super Wide Band (SWB) MIMO antenna is presented for Ultra Wideband (UWB) applications. Two planar elliptical patch antennas with Microstrip-fed are used as the elements of the MIMO antenna. Ground planes and the radiating patch elements are on the same side of dielectric substrate whose relative permittivity (εr) is 3.38 which is a RO4000® series high frequency circuit material. The proposed antenna occupies a wide usable fractional bandwidth of more than 170.7% (2.37-30 GHz) which covers UWB frequency range for all types of UWB applications. Performance analysis of designed antenna is carried out in free space in terms of reflection coefficient, radiation pattern and voltage standing wave ratio (VSWR) and the results show that, this antenna could be a very suitable one for UWB applications.
Speed Control for SPWM-VSI Fed Induction Motor Taking Core Loss and Stray Load Losses into Account
Md. Rifat Hazari
American International University-Bangladesh, Bangladesh
Mohammad Abdul Mannan
American International University-Bangladesh, Bangladesh
Toshiaki Murata
Kitami Institute of Technology, Japan
Junji Tamura
Kitami Institute of Technology, Japan
Abstract
To control the flux and the torque precisely based on the FOC, core losses (CL) and stray load losses (SLL), which are generally neglected, should be considered in the mathematical model of IM to design the controller. In this paper, a discrete time multi input multi output (MIMO) optimal regulator is proposed based on the state space equations of IM taking CL and SLL into account. IRFOC technique is used to design the proposed controller. The performance of the designed controller is verified by the simulation studies which have been done by using Matlab/Simulink.
Design and Simulation of a Dual-stage DC to DC Boost Converter Driven Micro Grid Tie Inverter
Zaber Hasan Mahmud
American International University-Bangladesh, Bangladesh
Md. Kamrul Hassan
American International University-Bangladesh, Bangladesh
Abstract
The paper represents a single phase and transformer-less photovoltaic (PV) grid-tie inverter for residential application, the output of which is 220 V rms at grid to meet the future power crisis and hence named as a micro grid tie inverter. The simulation result using PSIM ensures that the frequency of the inverter output voltage is exactly 50 Hz with a magnitude of 220 V rms and is in phase with the grid voltage. The total harmonic distortion (THD) of the inverter output is less than 0.1% and the efficiency of the inverter also increases up to 98% which is obtained through an inverter circuit design by employing a PV panel, a dual-stage switch mode boost converter, a voltage divider circuit, an H-bridge inverter and a T-LCL filter circuit.
Speed Control of Separately Excited DC Motor with Efficiency Maximization Propensity
Sumaiya Umme Hani
American International University-Bangladesh, Bangladesh
Md. Kamrul Hassan
American International University-Bangladesh, Bangladesh
Md. Rifat Hazari
American International University-Bangladesh, Bangladesh
Mohammad Abdul Mannan
American International University-Bangladesh, Bangladesh
Abstract
DC motors are exceptionally eminent in various applications where speed is the foremost aspect such as industrial applications, robot manipulators and home appliances. The supreme advantage of dc motors is having the control over speed. For a DC motor, there are many systems to signify the machine behavior with good accuracy. In order to maximize the efficiency of the DC motor with an appreciable speed control, it is essential to trail the optimized field current for various operating point with the help of a field controller. This paper contains the proposal of designing a speed controller named Multi Input and Multi Output Optimal Regulator, which holds better performance, zero overshooting and reduced steady state error forth. The paper also deals with efficiency maximization overture for DC motor. State space model of DC motor is constructed, which in turn used for designing the proposed controller. Using the MATLAB/SIMULINK contrivance, all the simulations are verified and this puts into evidence that the proposed controller is simple, reliable and robust.
Measurement of Content Distribution in the Internet
Md Hasib Noor
American International University-Bangladesh, Bangladesh
Miftah Al Karim
American International University-Bangladesh, Bangladesh
Saiful Islam Khan
American International University-Bangladesh, Bangladesh
Abstract
As Content Delivery Networks and P2P architectures take a leading role in today's Internet development, an important aspect that has been under research, so it is essential to investigate the measurement techniques of this kind of infrastructures. Researchers are interested in deploying further research in these areas and therefore a deep knowledge about the tools, methodologies and frameworks used to make measurements in such networks is more than necessary .It is also required to have real datasets of P2P and CDN ecosystems as well as the methods to detect anomalies and the projected solutions; so the goal of this project is to make a survey on the relevant work in characterizing different such ecosystems.
Crystallographic Orientation-dependent Optical Properties of InGaAs/GaAs Quantum Well Architecture by 4×4 Hamiltonian Matrix
S.M. Tasmeeh Ahsan
American International University-Bangladesh, Bangladesh
Mahmoodul Islam
American International University-Bangladesh, Bangladesh
Sourav Roy
Jessore University of Science and Technology, Bangladesh
Abstract
A methodical approach is introduced to establish energy dispersion relations with hole sub-band states and optical gain spectra for variant growth directions such as [001], [110], [1 1 2], [113] and [111] of compressively strained InGaAs/GaAs quantum well (QW) architecture by solving envelope function equation using finite difference method. It is demonstrated that there is a substantial correlation between optical gain and its emission wavelength amidst a particular crystal orientation of the QW. From the MATLAB simulation results, it can be settled that the dispersion relation between hole sub-band states, optical gain, and the threshold current density in [1 1 1] direction deviates exclusively from the other directions, in particular, the more conventional [0 0 1]. The regular optical gains are inspected 3100, 3080, 2700, 3300, and 2800 cm-1 in [0 0 1], [1 1 0], [1 1 1], [1 1 3], and [1 3 1] crystal orientations, respectively, when the injection carrier density is 2 × 1018 cm-3. Eventually, the highest optical power and the lowest threshold current are attained in orientation [1 1 3] while the number of quantum well is five.
Nilima Rahman
American International University-Bangladesh, Bangladesh
M. Tanseer Ali
American International University-Bangladesh, Bangladesh
Abstract
In this paper, a new design methodology based on X-parameter is presented. X-parameters are developed as an extension of S-parameters capable of modeling non-linear devices driven by large signals. A class-A power amplifier with single MOSFET is designed. The limitation of S-parameter is shown by simulating this designed power amplifier. A new amplifier linearization technique based on the negative impedance compensation has been demonstrated. This paper carries the comparison results between with negative impedance and without negative impedance. All the circuitry level simulations have been implemented by using Agilent ADS software. An effective Two Tone nonlinear simulation and measurement results show that, with this proposed technique linearity is improved by 9.39 dBm and gain is improved by 3.69 dB as well as power of the spectrum curve, adjacent channel power ratio (ACPR) is improved by 4 dBm.
Performance Improvement of Power System Network by Placing Unified Power Flow Controller at Appropriate Location
Shameem Ahmad
American International University-Bangladesh, Bangladesh
Saad Mekhilef
University of Malaya, Malaysia
Fadi M. Albatsh
University of Malaya, Malaysia
Shuvra Saha
American International University-Bangladesh, Bangladesh
Abstract
This paper presents a dynamic model of UPFC to enhance performance of power system in terms of power flow capability or voltage stability where its location has been determined by employing two line stability indices (LSIs) known as Fast Voltage Stability Index (FVSI) and Voltage Collapse Point Indicators (VCPI). These indices have been exploited dynamically to find out the weakest links of the power system network which are prone to voltage instability. The control algorithms for both series and shunt converters of UPFC are designed based on PI controller. To investigate the performance of UPFC on the enhancement of voltage stability, dynamic simulations has been carried out in PSCAD/EMTDC software. IEEE-5 and IEEE-14 bus systems have been selected for case studies. The locations have been found using FVSI and VCPI for UPFC placement proved to be the best locations through the simulation results which have also exhibited the improvement in power system performance.
ZigBee: Simulation and Investigation of Star and Mesh Topology by using different Transmission Bands
Md. Mamunur Rashid
American International University-Bangladesh, Bangladesh
Rethwan Faiz
American International University-Bangladesh, Bangladesh
Abstract
ZigBee is based on an IEEE 802.15.4 standard and it is used to create Personal Area Networks (PAN) built for small, low-power digital radios. ZigBee operates in three different industrial, scientific and medical (ISM, unlicensed) radio bands: 868 MHz (EU and Japan), 915 MHz (ISM, US) and 2.4 GHz (Worldwide). The supported data rates of these three bands are 20 Kbps, 40 Kbps and 250 Kbps respectively. In this paper, three types of bands are experimented in star and mesh topology and performance metrics like throughput, delay etc. are measured using OPNET simulator.
Varying Sample-Width to Realize Area-Efficient FPGA Realization of Sobel-Fieldman Edge Detector
Kazi Ahmed Asif Fuad
American International University-Bangladesh, Bangladesh
Shahriyar Masud Rizvi
American International University-Bangladesh, Bangladesh
Abstract
Multiple gradient-based edge detection algorithms exist today with Canny and Sobel-Fieldman being the most popular. These algorithms can be realized in software using MATLAB or OpenCV and also in hardware using either direct RTL (Verilog/VHDL) or hardware/software co-design, which generates RTL from block-level descriptions. We realized Sobel-Fieldman algorithm in Spartan-6 FPGA (from Xilinx) using HW/SW co-design tool Xilinx System Generator (XSG) coupled with Simulink. We presented new implementation approach for area-efficient FPGA realization of Sobel-Fieldman algorithm by manipulating sample-widths of input. After varying sample-widths we find that some smaller sample widths generate images of a quality that is identical to ones attained from standard sample-width (16:14) but with sufficiently lesser FPGA resources. The sample-width of (6:4) generates images of quality attained in standard sample-size of (16:14) with 27% lesser no of LUTs, 25% lesser no of registers and overall 21% lesser slices.
Impact of Urban Canyon on the Micro Climate: A study through ENVI-met Model in the Context of Dhanmondi, Dhaka
Saiful Hasan Tariq
American International University-Bangladesh, Bangladesh
Syma Haque Trisha
Bangladesh University of Engineering and Technology, Bangladesh
Zarrin Tasnim
J.A. Architects ltd., Bangladesh
Abstract
Dhanmondi is one of the prime residential areas of Dhaka City characterized by diverse road pattern with primary, secondary and tertiary arteries, open spaces and variation in porosity in urban fabric. Satmasjid road is the primary road that runs through the Dhanmondi Residential area and retains the character of the urban canyon of 30m-40m width and 20m-40m enclosure on both sides. There are vegetal canopy on road islands, robust open spaces and lakes alongside. The paper is based on the study conducted to understand the impact of urban canyon on the micro-climate of the surrounding area through a field survey along with the ENVI-met simulation model of the study area.
Creating New Eco-Cities for Sustainable Urban Development
Sharmina Haque
American International University-Bangladesh, Bangladesh
Tabassum Zarin
American International University-Bangladesh, Bangladesh
Abstract
More than half of the world’s population now lives in urban areas and the number is expected to continue growing. To accommodate population and economic growth in the cities, two prominent development trends seem to be emerging. One is, an approach that primarily seeks to optimize existing infrastructure and improving the city's environment, with a focus on managed intensification through compact developments, urban regeneration and Brownfield redevelopment. Other involves developing new towns or eco-towns away from existing areas, usually on Greenfield sites in the rural or agriculture hinterland. But there are arguments between proponents about the two approaches of development. This paper explores the paradigms that influence the development of the concept of building new Eco-Cities. It tries to discuss the popular notion that well-planned, comprehensive eco-towns offer the most sustainable way for fast -growing cities, and present the analysis on how they address the critical issues of social, economical and environmental sustainability.
Bring Back Nature in the Post Mining Landscape of the West Rand, Johannesburg
Md Sariful Islam
American International University-Bangladesh, Bangladesh
Tabassum Zarin
American International University-Bangladesh, Bangladesh
Sharmina Haque
American International University-Bangladesh, Bangladesh
Abstract
West Rand, Johannesburg in South Africa, the city which is famous for its celebration of gold mining for more than hundred years, but this growing situation of gold mining is creating a great deal of destruction and degradation of natural habitats and elimination of different species of plants with wildlife from this territory. In recent years the government and private developers are aware about post mining sector. Rehabilitation and alternate use of unused mine residue area are burning issues of Johannesburg. Environmental impacts like acidic water, toxic soil and polluted air are discussed again and again to reclaim the mining landscape [1]. Affordable housing for poor or utilize large portions of the area for industrial purpose is proposed to use these lands for productive purposes. Unfortunately, bring back the wildlife or regenerate the landscape as forest, woodland, savannah, grassland and wetland is rarely discussed as tools to reclaim the mining belt. But this landscape has the possibility to rejuvenate the nature together with solving the contamination problem. Environmental problem can be treated through the use of plants known as 'Phytoremediation' that mitigate the problem without the contaminant material excavation and dispose of it elsewhere [2]. Sensible modification of topography can create a harmonious condition to improve the quality of vegetation and wildlife habitation. This paper emphasizes the importance of bringing back nature and the possible options to achieve the goal.
Creating Connectivity in Urban Renewal Places: The Case of Central Footscray
Hasnun Wara Khondker
American International University-Bangladesh, Bangladesh
Mohammed Azizul Mohith
American International University-Bangladesh, Bangladesh
Ashik Vaskor Mannan
American International University-Bangladesh, Bangladesh
Abstract
Footscray, the former manufacturing hub of Victoria, Australia has lost its previous glory and economic strength due to shifting of the manufacturing industries overseas. As a result, this area now becomes the address of relatively disadvantaged people of Melbourne including minor communities, recent migrants and international students. Inadequate community facilities and lack of connectivity linkages within the area, together with its underprivileged residents are causing detrimental consequences on Footscray by creating safety concerns and social issues like public drinking, crimes, violence and isolation. The aim of this research is to check, if creating connectivity between places and activating public realms to initiate passive surveillance and public interaction would eventually reduce crime and other social problems of the area. Hence, this paper would document key connectivity issues and barriers taking Central Footscray as the focus area and recommend strategies to improve public realms and activate urban spaces through accessibility and connectivity.
From ‘Urban Space’ to ‘Urban Place’: The case of Gulshan South Park, Dhaka, Bangladesh
Md Sariful Islam
American International University-Bangladesh, Bangladesh
Sudipta Barua
American International University-Bangladesh, Bangladesh
M. Arefeen Ibrahim
American International University-Bangladesh, Bangladesh
Dilruba Fredous Shuvra
American International University-Bangladesh, Bangladesh
Abstract
What turns an urban space into an urban place? With an intention to explore the aspects that persuades people to transform an urban space into an urban place in a socio-cultural context like Dhaka a research was done from 2006 to 2015. This paper is based on that study. In our search for production of urban place, a neighborhood park namely ‘Dr. Fazle Rabbi Park’ and popularly known as ‘Gulshan South Park’, is chosen as a case study. By virtue of its location, the Gulshan South Park is serving as a recreational space of three residential areas of Dhaka: Gulshan, Niketon and South Badda. Regardless of its earmark in the plan of Gulshan Model Town of 1962, Gulshan South Park remained as the most hideous public park on account of 25-year long illegal occupancy. In 2010, the city government of Dhaka, the Dhaka City Corporation (DCC), turned the park into a pulsating urban space. Both pre and post design state of Gulshan South Park were investigated. The study revealed that, the provisions of pathways, outdoor furniture (tables and benches), vegetation, lights, and see-through boundary wall that are applied by Gulshan Society and their proper maintenance influenced the community people inhabit the park with their activities and thus turned this space into lively place. The paper concludes with the propositions for available urban places and thus brings them into public realm. In this light, based on analyzed design forms, observed activities, and interviewed users of Gulshan South Park, a performance based recommendations rather than prescriptive recommendations are presented to guide the development of available urban spaces for the well-being of urban population of Dhaka.
An Efficient DNA Sequence Compression Method Based on Approximate Repeats and Reverse Complements
Md. Rafiqul Islam
Khulna University, Bangladesh
Md. Inzamam-ul-Hossain
North Western University, Bangladesh
Kishore Kumar Pal
Atom System Ltd., Japan
Abstract
An efficient technique for DNA sequence compression based on approximate repeats and reverse complements has been developed. Instead of using separate edit operations for approximate repeats and reverse complements, one operation for each type of mismatch and use of Look-up Table for non-repeat subsequences are proposed. To get better compression ratio, we use arithmetic coder for final encoding process. Our method is the enhancement of DNACompress that uses separate edit operation for each mismatch character in a subsequence. With this approach, we can get better compression ratio and less execution time. Experimental results show that this method can efficiently compress DNA sequences with less execution time. Basically, compression of non-repeat subsequences with Look-up Table gives less execution time and considering one edit operation for each type of edit operation gives better compression ratio. In the proposed method time complexity and compression ratio are better than those of GenCompress and DNACompress. The decompression process is effective and efficient in this method. It is the reversible process of compression process. We show in the experimental results that the decompression process also requires less execution time than the existing methods.
OTR: A Transparent Database Approach for using Ontology in Information Systems
Bayzid Ashik
American International University-Bangladesh, Bangladesh
Md. Asif Uddin
American International University-Bangladesh, Bangladesh
Tanmoy Mandal
American International University-Bangladesh, Bangladesh
Khaled Md. Tuhidul Hossain
American International University-Bangladesh, Bangladesh
Abstract
Ontology is acquiring importance and commencing popularity as a common vocabulary and open source model. On the other hand RDBMS (Relational database management system) is renowned for worldwide software development. Transparent database conceals complexity and renders opportunity to interchange between database platforms to adopt welfare from all platforms. In order to aggregate both the characteristics of ontology and RDBMS, a new and efficient algorithm as well as a new software tool for database transparency is suggested to commute ontology OWL (Web Ontology Language) database to RDB (Relational database) and RDB to OWL. Besides general software cannot use ontology based database owing to its complication which lead to resolve the problem by using OTR (OWL to RDB converter), an adjuvant tool to convert OWL to RDB. OTR constitutes an intermediate XML file from OWL then retorts SQL (Structured Query Language) from it. Therefore software can be formulated based on ontology.
X-Rays and Other Associated Techniques in Identifying Organic Compounds for the Production of Synthetic Graphite
Rutaba Jania
American International University-Bangladesh, Bangladesh
Tafazzal Hossain
American International University-Bangladesh, Bangladesh
Abstarct
The main objective of this paper is to study the graphitizibility of organic compounds. The author has considered the following technique by introducing XRD, DTA, Polarized light micrography, D-Cconductivity measurement. Graphitizable organic materials like anthracene, crycene, phenanthrene, coal etc are characterized by their transition through a liquid or plastic state of optical anisotropy called’carbonaceous mesophase’as a prerequisite to graphitization. X-ray analysis has been carried out to see that inter-layer spacing of graphite making carbons decreases with increase of temperature and ultimately becomes 3.3540A or nearly so, in the graphitization temperature range 2500°C to 3000°C.Sensitive tint method of the reflected polarized-light technique has also been found suitable to study the initial formation of spherules, their coalescence and mosaic formation during mesophase period. Differential thermal analysis (DTA) has been employed for detecting the graphitizability of the substance as well as to determine the temperature intervals of mesophase, the life time of which is limited by its hardening to a semi coke.DTA trace of graphitizable organic compounds shows an initial large endotherm with activation energy of the order of 60 kcal/mole or above except a very few exceptions. In graphite–making organic compounds there is a sharp fall of resistivity as temperature increases showing a semi-conducting behavior.
Non-Newtonian Casson Fluid Heat and Mass Transfer Flow and Viscous Dissipation with a Binary Chemical Reaction
American International University-Bangladesh, Bangladesh
American International University-Bangladesh, Bangladesh
Abstract
A similarity solution of a binary chemical reaction on unsteady non-Newtonian Casson fluid flow with heat and mass transfer past a flat porous plate is investigated. The effects of Casson parameter on the velocity profiles for both cooling and heating problems are studied and we also study the effects of Eckert number, chemical reaction rate and Arrhenius activation energy on the temperature and concentration respectively in this paper. The governing partial differential equations are reduced to ordinary differential equations by introducing locally similarity transformation [ Maleque [35]]. Numerical solutions to the reduced non-linear similarity equations are then obtained by adopting sixth ordered implicit Runge-Kutta and shooting method using the Nachtsheim- Swigert iteration technique. The results of the numerical solution are then presented graphically in the form of velocity, temperature and concentration profiles. The corresponding skin friction coefficient, the Nusselt number and the Sherwood number are also calculated and displayed in table showing the effects of various parameters on them.
Modification of Ahmed Car Body for Reducing Drag
Abul Kalam Azad
Rayermohal College, Bangladesh
Mohammad Arif Hossain
Khulna University of Engineering & Technology, Bangladesh
A. K. M. Sadrul Islam
Islamic University of Technology, Bangladesh
Abstract
Method of passive control can be applied to reduce aerodynamic drag of a vehicle. It provides the possibility to modify the flow locally, to remove or delay the flow separation or to reduce the development of the recirculation zone at the rear as well as the separated swirling structures around the body. In this context, flow control by transversally placed channel is applied on the rear part of the body. In this study, the Ahmed body is used as a model. The k-ε turbulence model is used in the computational simulation. In this configuration the rear part of the body was inclined at an angle of 250 with respect to the horizontal plane. The Ahmed body is placed in a 3D- rectangular numerical domain with length, width and height equal to 31.925H, 6.493H and 4.861H respectively, where the body height H = 0.288m. In this simulation a roughness height of 0.0002m is used, where the inlet velocity of the fluid is 40m/s. The result shows that approximately 2.93% drag coefficient can be reduced in this method.
