Dissertations/Theses - Department of Mechanical Engineering

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Acoustics of rectangular flat plates
(Department of Mechanical Engineering, 1988-04) Alauddin Ahmed; Wahhaj Uddin, Dr. Md.
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Acoustics of rectangular flat plates of mixed boundary conditions
(Department of Mechanical Engineering, 1989-04) Mandal, Nirmal Kumar; Wahhaj Uddin, Dr. Md.
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Acoustics of rectangular flat plates with free-simply supported and clamped-simply supported edge conditions
(Department of Mechanical Engineering, 1989-08) Khalilur Rahman, Md.; Wahhaj Uddin, Dr. Md.
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Adaptation of ring spinning in the flyer spinning machine for making fine jute yarn
(Department of Mechanical Engineering, 1997-09) Osman Ghani Miazi, Md.; Sarkar, Dr. M. A. Rashid
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Aerodynamic characteristics of a five bladed S-shaped savonius rotor
(Department of Mechanical Engineering (ME), 2016-03) Nayem Ashraf, MD.; Quamrul Islam, Dr. Md.
The S-shaped rotor is a modification of the Savonius rotor with no overlap. Drag and torque coefficients of a five bladed S-shaped Savonius rotor have been investigated by measuring the pressure distribution on the blade surfaces for various rotor angles. The experiments have been carried out at a Reynolds number of 2.1x105 in a uniform flow jet produced by an open circuit wind tunnel. To calculate drag force and torque in non-dimensional form, the data are taken on 12 pressure tapping points on each blade of the five bladed S-shaped Savonius rotor for every 100 interval of the angle of rotation. The pressure distributions both on the concave and convex surface of the blade at different angle of rotation are presented graphically. At rotor angle α = 400, difference of pressure coefficient on convex surface and concave surface is maximum. At rotor angle α = 3100, difference of pressure coefficient on convex surface and concave surface is minimum. The measurements indicate that drag forces and the torque, vary with rotor angle. The normal drag coefficient increases with the rotor angle, reaches its maximum value at the rotor angle α = 400, remains approximately constant value at the rotor angle α = 1400 to 2100 and minimum value at the rotor angle α = 3100. The tangential drag coefficient increases with the rotor angle, reaches its maximum value at the rotor angle α = 2900 and minimum value at the rotor angle α = 00. The torque coefficient also increases with the rotor angle, reaches its maximum value at the rotor angle α = 400, remains approximately constant value at the rotor angle α = 1400 to 2100 and reaches minimum value at the rotor angle α = 3100. The result facilitates predicting the performance of five bladed S-shaped Savonius rotor under dynamic conditions.
Aerodynamic characteristics of a four bladed savonius rotor
(Department of Mechanical Engineering, 2003-11) Humayun Kabir Bhuiyan, Md.; Quamrul Islam, Dr. Md.
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Aerodynamic characteristics of a transonic airfoil cascade
(Department of Mechanical Engineering (ME), 2016-12) Saha, Sudarshan Chandra; Hasan, Dr. A. B. M. Toufique
The trend towards higher pressure ratio and compact turbomachines with a reduced number of stages leads to a considerable increase of aerodynamic loading of the airfoil cascades. Thereby the velocities relative to the blades increase to transonic and supersonic speeds and shock-waves occur within the airfoil cascade. These shock waves could interact with the airfoil surface boundary layer and can cause unsteady boundary layer separation. In fact, Shock wave–boundary-layer interactions (SBLIs) occur when a shock wave and a boundary layer converge and since both can be found in almost every supersonic flow, these interactions are commonplace. The most obvious way for them to arise is for an externally generated shock wave to impinge onto a surface on which there is a boundary layer. In the transonic regime, shock waves are formed at the downstream edge of an embedded supersonic region; where these shocks come close to the surface, a SBLI is produced. In any SBLI, the shock imposes an intense adverse pressure gradient on the boundary layer, which causes it to thicken and possibly also to separate. SBLI also causes flow unsteadiness. Shock induced oscillations (SIO), aerodynamic instabilities, high cycle fatigue failure (HCF), non-synchronous vibration (NSV), aeroacoustic noise and so on are the detrimental consequences of this unsteady shock wave boundary layer interaction. On transonic wings, it increases the drag and has the potential to cause flow unsteadiness and buffet. In hypersonic flight, SBLI can be disastrous because at high Mach numbers, it has the potential to cause intense localized heating that can be severe enough to destroy a vehicle. Because of its significance for many practical applications, SBLI is the focus of numerous studies spanning several decades. Many of the investigations have been dealt considering an isolated airfoil in transonic flows. However, little information is available on the aerodynamics of airfoil cascades. The goal of the present research is to analyze and to understand the transonic flow phenomena in a circular arc airfoil cascade using experiments and numerical computation. Experimental tests were conducted to investigate the behavior of passage shock waves with the shock induced boundary layer separation in a supersonic wind tunnel flow facility. Further, a Reynolds averaged Navier- Stokes (RANS) solver was used to provide airfoil surface pressures, overall performance from wake characteristics and so on. Particular attention is to be paid on the embedded shock wave structure and an accurate simulation of the shock boundary layer interaction. The experiment was performed for unstaggered case and the numerical studies were performed for stagger or setting angle 0º to 20º. The results show that the self-excited shock wave oscillations occur in the cascade passage for a pressure ratio of 0.75 in both unstaggered and staggered case. Fluctuating pressure histories are recorded at different locations in the flow field. PSD from FFT calculation of the data is used to find the principal frequency of the unsteady behaviour. A frequency of 976 Hz is found to be the dominating frequency.It is observed that for all the cases, the flow field remains undisturbed from leading edge to x/c=0.50, as in that portion no shock wave is observed on the airfoil surfaces. For different stagger angle, peak RMS of pressure oscillation (prms/q0) is calculated and its location is identified. Flow separation occurs at a distance after the shock wave. Separation points and separation lengths are also calculated. Wave drags contribution is much higher than viscous drag at high speed compressible flow. Wave drag coefficients are also calculated for different flow conditions.
Aerodynamics characteristics of a vertical axis vane type wind turbine
(Department of Mechanical Engineering, 2008-04) Faizul Mohammad Kamal; Quamrul Islam, Dr. Md.
This research work has been carried out to study the aerodynamic characteristics and to analyze the effect on an equally spaced vertical axis four, five and six bladed vane type rotor. The aerodynamic characteristics i.e. torque coefficient, drag coefficient etc. of vertical axis vane type rotor have been studied in this present research work by measuring the pressure distribution on the blade surfaces at various rotor angles. The experiments have been carried out at a Reynolds number of 1.65 x 105 in a uniform flow jet produced by an open circuit wind tunnel. The pressure measurements have been made at 8 tapping points on each blade of the vane rotors. Pressure on the convex and concave surfaces have been measured for every 100 interval of rotor angle up to 3600 angle of rotation. The data obtained experimentally has presented in terms of non-dimensional coefficients. To calculate drag force and torque in non-dimensional form, computer based software has been used and the output have been subsequently plotted and analyzed. Aerodynamic characteristics on individual and group of four, five, six blades have also been determined in the present work. A quasi-steady approach has been applied for studying the dynamic performance of the rotor at different rotor angle using the static drag and torque coefficients. Power coefficient versus tip speed ratio curve for four, five and six bladed vane type rotor has also been drawn. Power coefficient versus tip speed ratio of the present measurement and the previous researcher's works has plotted on the same graph for comparison. This method results in a reasonable agreement with the previous measurement.
Aerothermal analysis of supersonic flow around an airfoil in transitional rarefied conditions
(Department of Mechanical Engineering, 2020-01-18) Salehin, Musfequs; Hasan, Dr. A.B.M. Toufique
When the physical length scale of a fluid mechanical system becomes comparable to the molecular mean free path (the average distance traveled by each molecule of gas between successive intermolecular collisions), the system could not able to attain the flow and thermodynamic equilibrium conditions. Such cases are known as rarefied conditions. In general, these rarefied conditions occur when the gas flow is at very low density (low pressure) environment and/or involves very small length scales such as- flight of high-speed vehicles at very high altitude in the earth’s atmosphere, micro- and nanoelectromechanical systems (MEMS/NEMS), flow around spacecraft thrusters, and so on. In rarefied gas flows, the discrete particle effects (representing atoms and molecules of gas) become dominant and a sharp gradient of the macroscopic quantities such as velocity, temperature, pressure and so on are observed. As a result, the well-established continuum descriptions of gas flows that take into account the molecular behavior in an aggregate sense (bulk) collapse at rarefied conditions. Therefore, the mathematical modeling of such gas flows with Navier-Stokes (NS) equations becomes inaccurate. In these cases, the kinetic theory of gas i.e. the Boltzmann equation is to be considered to predict the rarefied flow phenomena which take into account the particle collisions and the post-collision molecular velocity distributions. The degree of rarefaction is defined by Knudsen number (Kn) which is defined as the ratio between the molecular mean free path and the characteristics length of the flow system. The continuum hypothesis is valid for very small values of Kn (Kn < 0.01); whereas the hypothesis breaks down at slip regime (0.01 < Kn < 0.1) and transitional regime (0.1 < Kn < 10). In this present work, supersonic flow over an airfoil in the transitional rarefied conditions has been studied. The aerothermal characteristics of the system have modeled and computationally solved using Direct Simulation Monte Carlo (DSMC) approach. The computations have been performed with ‘dsmcFOAM’ solver which is available in the open-source CFD software platform ‘OpenFOAM.’ ‘dsmcFOAM’ is a validated and widely used DSMC solver that is dedicated to solving the Boltzmann equation stochastically for the rarefied gas flow problems. A classical series of symmetric airfoil NACA 00XX has been considered. DSMC computation has been performed for three airfoils; namely- NACA 0012 (12% thick), NACA 0010 (10% thick) and NACA 0007 (10% thick) airfoils at 0o angle of attack (AOA). Supersonic flows with freestream Mach number in the range of M∞ = 2 – 4 and transitional rarefied conditions in the range of Kn = 0.5 - 5 are considered. The results have been validated with the available relevant experimental data as well as with the solution data from other DSMC computations. DSMC results showed that the shock waves which are obvious in the supersonic flow field around the airfoil vanishes in the transitional rarefied conditions and a series of diffusive waves are observed. These diffusive waves deviate the free stream flow properties from the airfoil leading edge. The surface-particles interactions which result the shear stress shows decreasing behavior with the increase of Kn. However, this stress was found to be increased with the increase of free-stream Mach number, M∞ for a particular degree of rarefaction (Kn). The cumulative effects of shear stress, pressure and compressibility are considered to determine the aerodynamic drag force. It is found that the aerodynamic drag increases with the increase of Kn at a fixed Mach number. On the other hand, for a constant Kn, a linear decrement of drag is found while Mach number increases. The non-equilibrium effects, i.e. velocity slip and temperature jump at the airfoil surfaces are identified by the present DSMC approach. Whenever the degree of rarefication (Kn) increases, the velocity increases at the vicinity of the airfoil surface which results in significant-velocity slip. At supersonic speeds, gas molecules accumulate at the leading edge of the airfoil and the macroscopic properties such as density, pressure and temperature increase. Moreover, at these speeds, a large number of molecules collide at the leading edge and their kinetic energy is transported into force action and heating. As the Mach number increases, the particle density at the airfoil leading-edge increases. However, the particle density decreases over the airfoil surface. The Kn number has effects on particle interactions with airfoil surfaces. At Kn = 5.0, the lowest amount of particle density linearly distributed over the airfoil surface is observed. At lower Kn number, gas molecules possess a larger amount of kinetic and internal energy which are responsible to affect the flow temperatures. Conversely, the molecules at higher Kn number have negligible kinetic and internal energy. The heat load, i.e. surface heat flux is higher for the slower particles within the viscous regime of the flow filed. Therefore, at lower Kn number, the airfoil surface encounters a higher heat load than a higher Kn number. Mach number has an adverse effect on heat flux. The higher Mach number provides higher heat flux at all the rarefied conditions studied here. Additionally, the thickness effects of the airfoil in the transitional rarefied condition have been investigated based on their aerodynamic performance and surface heat load. Consequently, the airfoil with lower thickness encounters optimum aerodynamic drag and surface heat flux.
Alternative arrangement of metered dosing fluid using centrifugal pump
(Department of Mechanical Engineering (ME), 2016-03) Arafat Islam, MD.; Ehsan, Dr. Md.
Positive displacement dosing pumps are extensively used in various types of process industries in Bangladesh. They are widely used for metering small flow rates of a dosing fluid into a main flow. High head and low controllable flow rates make these pumps suitable for industrial flow metering applications. However their pulsating flow is not very suitable for proper mixing of fluids and they are much more expensive to buy and maintain. Considering such problems some alternative techniques may be suggested to control the fluid flow of a typical centrifugal pumps including - throttling, variable speed drive, impeller geometry control and bypass control. Variable speed drive and impeller geometry control are comparatively costly and the flow control by throttling is not an energy efficient process. Bypass flow control can be an alternative means to control the dosing flow range. An arrangement of creating dosing flow was developed using a typical low cost centrifugal pump with bypass flow technique. A wide range of dosing flow control was attained using fixed pump geometry and drive speed. The returning bulk flow from the pump into the main tank ensured better mixing due to churning effect which may eliminate the need of separate agitators. In this project, performance of a dosing pump was evaluated and compared to an alternative arrangement of similar fluid flow from a centrifugal pump flow arrangement using bypass technique. Water was used as a working fluid of the pump. Experiments were performed in total four phases. The first phase consists of only performance evaluation of the dosing pump and it is found that, the range of the metered flow of the dosing pump is 22.4 -1.5 L/h at corresponding head of 0.7725-71.36 m. The power consumption is almost constant 72 watt. The maximum and minimum efficiency is around 4% and 0.01% respectively. In the second phase, performance study of the centrifugal pump was evaluated. The range of fluid flow rate is almost 2650-11.4 L/h at corresponding head of 0.973-28 m. The power consumption varies from maximum 677.92 watt to minimum 624.4 watt depending on the flow rate changes. The maximum overall efficiency is found around 13.5%. In order to reduce the discharge of the centrifugal pump, bypass flow arrangement has been established and the third phase of experiment was carried out. Similar types of flow rates could be possible to be attained by the arrangement and the new established flow range was found 2.66-23.01 L/h at corresponding head of 13.19-28.5 meter. The power consumption varies from maximum 677.92 to minimum 624.4 watt at this phase. Impeller diameter has been reduced to decrease the power consumption and new operating range has been established due to impeller modification, which varies form 2.83-22.05 L/h at corresponding head of 6.01 -14.0 meter. With the modification, the power consumption reduces by 40% compared to the centrifugal bypass arrangement without impeller diameter reduction. But it slightly decreases the overall efficiency. Operability of the modified system was tested at low voltage, which also showed improvement of overall efficiency and reduction of further power consumption by 32% compared to bypass arrangement with impeller modification only. The capital cost can be saved by this centrifugal bypass flow system is approximately 87.5% of the capital cost of the dosing pump. This alternate system is more cost effective in terms of capital investment.
An Approach for Classifying ECG Arrhythmia Based on Features Extracted from EMD and Wavelet Packet Domains
(Department of Mechanical Engineering, 2012-07) Raju Sinha; Shahnaz, Dr. Celia
Any disturbance in the activity of heart can cause irregular heart rhythm known as cardiac arrhythmia. Electrocardiogram (ECG) is one of the most promising tools for classi cation of di erent types of arrhythmia, which is necessary until it goes fatal and causes loss of life. For ECG arrhythmia classi cation, a wide range of signal processing techniques extracting features from time, frequency and time frequency domains have been reported in the literature. Since, ECG is a nonstationary signal, time frequency analysis can perform better than the conventional time or frequency analysis methods. But, development of a multi-class arrhythmia classi cation method, which is simple yet e ective in handling practical conditions such as lack of enough training dataset and random selection of training and testing dataset, is still a challenging task. ECG signals can be well modeled as self-a ned fractal sets which vary under di erent arrhythmia. Thus local fractal dimension (LFD) can be employed as a feature in classifying di erent ECG arrhythmia. In the empirical mode decomposition (EMD) domain, the basic functions are directly derived from the original signal without the knowledge of any previous value of the signal. Therefore, the Hurst exponent (HE) required for deriving a set of LFD features is calculated from the intrinsic mode functions (IMFs) obtained via EMD of ECG signals. Since, for better approximation of LFD, at least three IMFs are to be determined which is dependent on the length of the ECG signal, time-frequency analysis in the wavelet packet decomposition (WPD) domain is performed for calculating the HE as well as deriving a set of more e ective LFD features. Considering the complexity and ease of implementation as an important criterion, a feature set based on energy and entropy of only the 4th level detail WPD coe cients is found to be simple yet the highest capable of solving a multi-class ECG arrhythmia problem. Each of the proposed sets of feature when fed to Euclidean distance based classi er can classify di erent arrhythmia even with reduced training dataset as well as randomly selected training and testing dataset. Simulations are carried out to evaluate the performance of the proposed method in terms of sensitivity, speci city and accuracy. It is shown that the proposed method outperforms some of the state-of-the-art methods with superior e cacy.
Analysis of a Guided Deep Beam of Composite Materials
(Department of Mechanical Engineering, 2009-02) Muzibur Rahman, M; Ahmed, Dr. S. Reaz
Analytical solution scores the highest degree of importance in structural analysis. But the existing mathematical models for analytical solutions are still inadequate. Neither the beam theory nor the stress function approach can address the guided deep beam appropriately. Though, in many cases, the numerical techniques can well approximate the response, if analytical solution is possible, that remains as the highly desirable one. An ideal mathematical model called displacement potential formulation is used to develop a new scheme for analyzing guided simply-supported deep beam of isotropic as well as orthotropic materials with different loading and support arrangements. The results are then analyzed and the effect of fiber reinforcement and beam aspect-ratio on the distributions of displacement and stresses in the beam are investigated. Besides, taking into account the effect of Saint Venant’s principle, a new analytical scheme is developed to generate the solution of an unguided simply supported deep beam, in which the guided beam solution is considered as the limiting case of the unguided one. Solutions of the guided isotropic and orthotropic deep beams are obtained satisfying all the physical conditions of the beam appropriately. In the investigation of solutions, the guided ends of the beam are identified to be the most critical section in terms of stresses. The bending stress distribution is found highly non-linear near the guides. The shearing stress distributions assume the standard parabolic pattern. The stresses at the load transition section are found to be different from other sections of the beam. Finally, comparative studies are carried out to ascertain the reliability and credibility of the present displacement potential solutions with those of classical beam theory, standard theory of elasticity as well as numerical method. Here the numerical solution is obtained using the standard finite element method. The study reveals that the displacement potential approach is the most appropriate way to deal with the guided deep beams analytically. Results of the present analysis are claimed to be highly reliable and accurate, and thus will provide a reliable design guideline for deep composite beams with/without guides.
Analysis of a Laminated Composite Panel with Discrete Variable Stiffeners
(Department of Mechanical Engineering, 2013-02) Modak, Partha; Ahmed, Dr. S. Reaz
This research addresses a new analysis of the elastic field of laminated composite structures under the influence of discrete stiffeners at the bounding surfaces. In this work, theory of elasticity, a new potential function, constitutive relations for composite materials, special lamination theory and finite-difference computational algorithm are integrated to develop a new computational scheme for stress analysis of laminated composite structures. Specific contribution are follows: A new mathematical formulation is developed for the analysis of structural components of laminated composites with mixed and changeable boundary conditions. In this formulation, the displacement components of plane elasticity are expressed in terms of a single potential function, which satisfies one of the equilibrium equations automatically. The remaining equilibrium equation is transformed into a fourth order partial differential equation of the unknown potential function. Thus the mixed boundary value plane elasticity problem is reduced to the solution of a single fourth order partial differential equation. The finite difference technique is used to develop an efficient computational algorithm based on the potential function formulation. A general computer program is developed based on the finite difference computational algorithm, which is capable of dealing with almost all the special cases of composite material, namely orthotropic and anisotropic lamina, angle-ply and cross-ply symmetric laminates, symmetric balanced laminates, etc., with mixed and changeable physical conditions at the surfaces of the structural composites. The application of the computational scheme is investigated to stress analysis of disxxi NOMENCLATURE xxii cretely stiffened panels of laminated composites. A number of practical problems of interest are solved and results are presented in the form of graphs. The problem includes symmetric and antisymmetric discretely stiffened laminated cantilever under shear loading, a laminated panel with periodic axial stiffeners subjected to eccentric loading and a laminated cantilever panel with discrete variable stiffeners. Finally, in an attempt to validate the new computational method, the potential function solutions are compared with both analytical and numerical solutions obtained by standard computational method. For this purpose, finite element solutions are obtained using the commercial FEM software, SAP2000. For all the problems, both the numerical solutions are found to be in excellent agreement with each other, which in turn, establishes the suitability and appropriateness of the present potential function computational scheme.
Analysis of a simply-supported thick composite beam with stiffened lateral ends
(Department of Mechanical Engineering, 2014-05) Abdullah Al Mamun; Ahmed, Dr. S Reaz
This thesis deals with the analysis of stress and displacement fields of a mixed boundaryvalue problem of fiber-reinforced composite materials. More specifically, the elastic field of a thick stiffened simply-supported composite beam is investigated using an efficient analytical scheme based on displacement-potential field formulation. In the present displacement-potential approach, the elastic problem of composite materials is formulated in terms of a single potential function of space variables, which is defined in terms of the displacement components of plane elasticity. Accordingly, all the parameters associated with the solution, namely stress, strain and displacements are expressed in terms of the same potential function, which eventually reduces the plane problem to the determination of the potential function from a single partial differential equation of equilibrium. The solution of the equilibrium equation is obtained in the form of infinite series, the coefficients of which are determined by appropriately satisfying the boundary conditions at different edges of the beam. Analytical expressions of the elastic field of the simply-supported beam are derived in terms of the potential function using Fourier series. Solutions are obtained for two different types of stiffeners (axial and lateral stiffeners) at the opposing lateral ends of the beam. Both the isotropic as well as fiber-reinforced composite materials are considered for the present analysis. Some of the practical issues of interest, like the effects of beam aspect ratio and stiffeners are discussed in relation to the composite beam. The analytical scheme is then extended to determine the fiber-orientation dependent stresses in stiffened simply-supported beam. Two limiting cases of fiber orientation ( = 0o and 90o) are considered for a wide range of beam aspect ratio. In an attempt to verify the reliability and accuracy of the analytical scheme developed, the present potential function solutions are compared with the corresponding solutions obtained by classical beam theory and verified with two standard computational methods of numerical techniques. The four solutions are found to be in excellent agreement with each other for all the cases of stiffeners and fiber orientations considered, which eventually establishes the soundness and appropriateness of the analytical scheme developed.
Analysis of an oscillating squeeze flim between a rubber surface and a rigid
(Department of Mechanical Engineering, 2007-11) Muhannad Mustafa; Mahabubur Razzaque, Dr. M.
Squeeze film theories have often been a major area of interest in fluid mechanics. In the present thesis, effects of surface roughness and permeability of rubber block on leakage flow rate and hydrodynamic force developed in fluid film between a cylindrical rigid surface and a cylindrical rubber surface are analyzed. The modified Reynolds equation, Laplace equation and governing equation for three parameter viscoelastic model are solved simultaneously to obtain pressure developed in fluid film between the mating surfaces as well as in the porous matrix and viscoelastic deformation of rubber surface. Equations are discretized into finite difference equations and solved by Gauss-Siedel iteration. It is seen that with increasing standard deviation and center line average (CLA) of surface height of rubber block, load carrying capacity increases significantly developing huge hydrodynamic force in the fluid film. Leakage flow rate also decreases with increasing standard deviation and center line average (CLA) of surface height of rubber block. Whereas with increasing permeability of rubber block, load carrying capacity decreases significantly but leakage flow rate decreases slightly. The present analyses contribute to designing many engineering applications such as bearing, wet clutch and non-contacting face seal. The results obtained from the present model are compared with experimental results available in the literature and a very good agreement is found.
Analysis of brittle fracture characteristics of an infinite plate with an FGM coating around a circular hole
(Department of Mechanical Engineering (ME), 2015-06) Shahereen Chowdhury; Ali, Dr. Md. Afsar
This study is concerned with the brittle fracture characteristics of an infinite plate with a functionally graded material (FGM) coating around a circular hole. The incompatible eigenstrain induced in the FGM coating after cooling from the sintering temperature, due to mismatch in the coefficients of thermal expansion (CTE), is taken into consideration. Two diametrically opposed radial edge cracks emanating from the circular hole are considered for the analysis of brittle fracture characteristic. A uniform internal pressure is assumed to be applied to the surfaces of the hole and cracks. The FGM coating is homogenized simulating the material nonhomogeneity by distribution of equivalent eigenstrain. Consequently, an approximation method of determining stress intensity factors (SIFs) is introduced representing the cracks by a continuous distribution of edge dislocations. This approximation method is used in analyzing the effects of material distribution in the coating, crack length, temperature, coating thickness and strength factor on fracture characteristics of the plate. Furthermore, apparent fracture toughness corresponding to prescribed material distributions is also analyzed as a function of the above mentioned parameters except for strength factor. To present numerical results, an infinite plate with TiC/Al2O3 FGM coating around a circular hole is considered. It is found that material distribution in the FGM coating around a circular hole has significant effects on the SIF and apparent fracture toughness which can be controlled by choosing the material distribution appropriately.
Analysis of data collected by LGED to determine the prospect of wind energy at Kuakata
(Department of Mechanical Engineering, 2009-02) Tanvir Hasan Dallas, Md.; Mamun, Dr. Mohammad
Energy Sector plays an important role in the development of socio-economic condition of the country. The supply of electricity by Bangladesh Power Development Board (BPDB) and Dhaka Electric Supply Authority (DESA) is mainly confined to cities and towns. Rural Electrification Board (REB) distributes electricity to the rural people through cooperatives. These rural co-operatives cover only 10% of the total population. Only about 15% of the total population is directly connected to the electricity supply. The waste material of plants, corn and animals, supply the major portion of the total energy. According to recent statistics, 73% of the final energy consumption was met by different type of bio-mass fuels (i.e. agriculture residues, wood fuel, animal dung etc.), 59% of the fuel is used for domestic purposes, 13.5% for small industrial products and 0.26% for non energy use; the latter is obviously very small covering commercial, transport and agricultural purposes. Rural, remote, coastal and isolated area development has long been considered as one of the maj or policy objectives of the Government of Bangladesh because over 85% of the populations live in those areas. In order to meet the increasing energy demand for development of agriculture and industry and for the generation of better employment opportunities, it will be necessary to harness all the available alternative sources of energy immediately.
Analysis of elastic field in structural elements of laminated composites by displacement potential approach
(Department of Mechanical Engineering, 2007-06) Nayeem Md. Lutful Huq; Ali, Dr. Md. Afsar
Composite materials drew attention of researchers from all over the world due to their outstanding advantages over conventional materials. They are being increasingly used as structural elements in almost all engineering applications. To take full advantage and ensure reliable performance of these materials in an application, it is indispensable to analyze various aspects of these materials. However, these are anisotropic and microscopically non homogeneous materials due to the presence of two phases in them. This makes the analytical investigation quite complicated due to mathematical difficulties. Therefore, only numerical and experimental approaches are extensively used in the field of composites, especially in the case of mixed boundary conditions. A reliable analytical method of analysis of these materials under mixed boundary conditions still seems to be lacking. In this study, an analytical method is developed to analyze the elastic field in structural c1cmcnts of laminated composite materials under mixed boundary conditions. The two displacement components of the two-dimensional elasticity problem are expressed in terms of a single displacement potential function, which satisfies one of the equilibrium cquations automatically. The other equilibrium equation is transformed into a fourth ordcr partial differential equation of unknown displacement potential function. Thus, the two dimcnsional mixed boundary value elasticity problem is reduced to the solution of a single fourth order partial differential equation. The solution of the fourth order partial diffcrcntial cquation is obtained in the form of Fourier series. To demonstrate the method, it is applicd to a rectangular panel consisting of (i) cross-ply laminated composite and (ii) angle-ply laminated composite. Analytical solutions of different components of stress and displacement are presented in the form of graphs. Further, the effects of laminate thickness, fiber orientation, and panel aspect ratio on the components of stress and displacement have been discussed in details. The results conform to the intuitively cxpected characteristics of the structures which verify that the method developed in the study can be applied reliably to structural elements of laminated composites under mixed boundary conditions to analyze elastic field.
Analysis of energy storage performance of supercapacitors with crumpled graphene electrodes
(Department of Mechanical Engineering (ME), 2022-06-20) Khan, Abrar Amin; Rahman, Dr. Md. Ashiqur
The Electric Double Layer Capacitors (EDLC)are one of the most promising technologies now-a-days in the field of energy storage due to its excellent power density, great cyclability and faster charging-discharging. However, having a lower energy density than batteries leading researchers to optimize the performance of supercapacitors by enhancing their energy storage capability. Improving the electrode design of the supercapacitors has been the primary approach in this regard. In this study, to enhance the capacitive performance of supercapacitors, EDLC with crumpled graphene electrode has been designed with aqueous (NaCl) electrolyte. This study is performed with the aid of molecular dynamics (MD) simulation to analyze the influence of crumpled graphene electrode on the EDLC performance. The findings show that the proposed EDLC model possesses five times higher specific capacitance (16.351 F/cm-2) than the planar graphene. Better charging mechanism and higher ion accessible area are the reasons behind this improved performance. In addition, the effects of the degree of crumpling of graphene, inclusion of defects on the crumpled graphene surface, and the variation of surface wettability on the performance of the modeled EDLC are also examined. The effect of degree of crumpling is found to be that complete crumpling aids the capacitive ability of the EDLC. The most optimized structure of the crumpled graphene electrode is observed for an added vacancy of 20% which possesses an outstanding specific capacitance of 19.8F/cm-2. Finally, for the effect of surface wettability, it is observed that super-hydrophilic electrodes facilitate better electrode-electrolyte interaction and improves ion separation, leading to a superior performance than the hydrophobic surfaces. The major takeaway from the project is that it provides significant insight into the potential of crumpled graphene electrode-based EDLC and sheds light on the possibility of achieving the desired balance of high-storage and high-power energy.
Analysis of Non-linear Self-excited Vibrations for Multiple Degrees of Freedom Systems
(Department of Mechanical Engineering, 2010-03) Sayem Uddin, Md.; Ashiqur Rahman, Dr. M.
Dynamics of nonlinear self-excited vibrations for both two degrees of freedom system (2DOFS) and three degrees of freedom system (3DOFS) using nonlinear springs and dampers is treated as a boundary value problem (BVP) considering the self-exciting force as a function of displacement, velocity or combination of both and nonlinear displacement terms. Four different cases have been considered for this analysis. Each case comprises of four different conditions depending on selfexcited force function. For different cases, a comparative study is performed varying the values of parameters to find out whether the system is stable or not. Nonlinearity is also considered for both springs and dampers to check the effect on the system’s response. A code has been developed to determine the response of the system. Some parameters for system’s stability have been determined from the system’s response obtained from the results of the developed code. It has also been tried to identify some parameters for which the system always tends to be unstable. The system’s behavior has also been observed by changing the values of self-excited force coefficients. Numerical analysis using multi-segment integration technique also shows the various phase planes and limit cycles in case of Van der Pol equation for various values of damping term, ì. This validates the developed code in analyzing such problems.