Sharif Digital Repository

Extensive subsonic wind tunnel tests were conducted on a coplanar wing-canard configuration at various angles of attack. In these experiments, a 60° swept canard was placed upstream of a 60° swept main delta wing. This paper deals with the distribution of mean and fluctuating pressure coefficients on the upper surfaces of both the canard and the wing immersed in a variety of angles of attack. According to the results, presence of canard postpones the vortex formation and growth on the wing to higher angles of attack compared to the canard-off case. Due to the canard downwash field, the wing operates at lower effective angles of attack and therefore, its vortex breakdown is delayed. The... 

One of the most important subsystems in the air-breathing engines is the atomizers, which break the fuel into many droplets. It is well known that atomization quality has a significant influence on combustion characteristics such as stability limits, efficiency, and pollutant emission. Both jet and swirl injectors are applicable in gas turbine engines. The latter have been widely used for combustion chambers and the former are usually employed for fuel injection in the afterburner part. Since experimental and numerical study of atomizers could be complex and costly, a design methodology of atomizers based on empirical relations is still very advantageous and effective in reducing... 

The first notable megawatt class wind turbine, which was the pioneer of improvement in the blade performance in large wind turbines, appeared in Vermont. Nowadays, modern wind turbines are using blades with multi-airfoils at different sections. In this study, in order to indicate the best airfoil profile for the optimum performance in different sections of a blade, five popular airfoils, including S8xx, FFA and AH series, were studied. On the large-scale profile, shear stress transport K–ω model was applied for the simulation of horizontal axis wind turbines for different wind speeds. The aerodynamic simulation was accomplished using computational fluid dynamic method, which in turn is based... 

In this investigation, core-shell rubber particles and organically modified clay were added to an epoxy resin and the changes in mechanical behavior were studied. As expected, the yield strength of the organoclay-filled epoxies increased modestly with increasing clay content and the yield strength of the rubber-modified compounds decreased with rubber content. Interestingly, the compressive yield strength of epoxy resins containing both rubber particles and organoclay (a.k.a. hybrid nanocomposites) was found to be independent on organoclay content (up to 5 phr). The fracture toughness of organoclay-filled epoxies increased modestly with clay content and, as expected, the increases in... 

Diquaternarization of dipyrido-[2,3-a:2′,3′-c]-phenazine,(dppz) and its analogous dipyrido-[2,3-a:2′,3′-c]-dimethylphenazine,(dppx) using 1,3-dibromopropane afford new water-soluble derivatives of phenazine, propylene-bipyridyldiylium-phenazine (1) and propylene-bipyridyldiylium-dimethylphenazine (2). The compounds have been characterized by means of FT-IR, NMR, elemental analysis and conductometric measurements and their structure were determined by X-ray crystallography. The experimental studies on the compounds have been accompanied computationally by Density Functional Theory (DFT) calculations. The DNA binding properties of both compounds to calf thymus DNA (ctDNA) were investigated by... 

The aim of this paper is to investigate adhesion property between nano-layered filler and the polymer matrix using a combination of experimental and micromechanical models as well as the changes in yield strength and stiffness of a layered silicate-filled epoxy nanocomposite. The results indicate that addition of intercalated layered silicate particles increased Young's modulus and yield strength of the epoxy resin, although the increases in stiffness and yield strength are modest, 30% and 4%, respectively. In addition, experimental results were compared with predictive stiffening and strengthening models. The rule of mixtures provides an upper bound for the modulus in these materials, while... 

The new water-soluble derivative of pyrazino[2,3-f][1,10] phenanthroline has been synthesized and characterized by conductivity measurement, elemental analysis, FT-IR, 1H NMR, 13C NMR spectroscopic studies, as well as single crystal x-ray crystallography. Theoretical calculations have been performed using the density functional theory (DFT) in order to confirm the structure and understand the electronic structure of the synthesized compound. The DNA binding properties of the compound were investigated by absorption spectroscopy, melting temperature and viscosity measurements. The intrinsic binding constant, Kb, was determined as 7.84 × 103 M−1 at 298 K. Thermodynamic parameters showed that... 

The performance of an HTPB/N2O hybrid motor was experimentally investigated. A hybrid motor was designed and manufactured in a laboratory with the purpose of studying the effects of various parameters on the motor's performance, including fuel regression rate and specific impulse. A series of tests were conducted to find a correlation between the fuel regression rate and the oxidizer's mass flux. The effects of chamber's pressure on the regression rate as well as other performance parameters were investigated. While the burning rate did not change dramatically, both the efficiency and ISP of the motor increased. The local fuel regression rate and the fuel port were also calculated. In... 

A study was conducted to report an observation on the effect of nanoclay fillers on the α-relaxation in an epoxy resin. The observation provided useful facts about glass transition processes in nanoclay-filled epoxy composites. The investigation involved the synthesis of intercalated-exfoliated clay-epoxy compounds, by swelling an organophilic montmorillonite in an aromatic epoxy resin and polymerization. The epoxy resin used in the study was a diglycidyl ether of bisphenol A (DGEBA), EPON 828, with an equivalent weight of 184-190 g/eq from Hexion Specialty Chemicals. The epoxy resin was cured with piperidine, obtained from Sigma-Aldrich. Nanomer® 1.30E. An octadecyl amine treated... 

Swage autofrettage process is used for internal forming and sizing of thick-walled tubes designed to withstand high internal pressures. In this process, a mandrel with a diameter slightly larger than that of the tube is pressed inside the tube and in so doing, creates the internal profile. This paper presents an experimental and numerical study of this process. Two dimensional axi-symmetric and three dimensional finite element analyses are used to investigate the effects of workpiece and mandrel geometry on the forming load and part quality. Experiments are carried out to validate the numerical results. © 2005 Elsevier Ltd. All rights reserved  

An extensive experimental investigation was conducted to study the effects of Dielectric Barrier Discharge (DBD), on the flow field of an airfoil at low Reynolds number. The DBD was mounted near the leading edge of a section of a wind turbine blade. It is believed that DBD can postpone the separation point on the airfoil by injecting momentum to the flow. The effects of steady actuations on the velocity profiles in the wake region have been investigated. The tests were performed at α = 4 to 36 degrees i.e. from low to deep stall angles of attack regions. Both surface pressure distribution and wake profile show remarkable improvement at high angles of attack, beyond the static stall angle of... 

In this investigation, the mechanical and thermal properties of the montmorillonite-epoxy nanocomposites were studied. The epoxy compounds were prepared by in situ polymerization and the intercalation dispersion were obtained as evidenced using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal remarkable stiffening effect and slight toughening effect of the MMT in the epoxy resin and an insight about the crack tip and notch tip toughening mechanism. According to the DMA, the glass transition temperature increases as increasing the MMT content. © 2008 World Scientific Publishing Company  

A mathematical model was introduced to describe the heat transfer behaviour of moist wheat bran beds. Comparison of predicted transient temperature profiles with experimental data collected in a simulated bed was used to evaluate bed thermal conductivity at various conditions. This parameter was correlated with the bed density and moisture content via a mathematical relation. Furthermore, extent of error in thermal conductivity evaluation resulted from neglecting water vapour diffusion was quantified. Results provide useful means to design, analyse, and predict the behaviour of solid state fermenters in a more reliable manner. © 2005 Institution of Chemical Engineers  

This paper presents a novel method fortuning the parameters of an sliding mode (SM) controller to obtain near-optimal performance. In order to do so the Linear Quadratic Regulator (LQR) was implemented on a linearized system. The input history of the LQR was used as a reference to obtain an optimal space for sliding mode controller parameters. Afterwards, the optimal space boundaries were dedicated to Genetic Algorithm (GA) to search for the optimal parameter for the nonlinear model. Also, the center of the obtained optimal space was used as an initial guess to the Particle Swarm Optimization (PSO) Algorithm. The proposed algorithm was implemented to regulate SM controller for the attitude... 

This paper discusses the mission requirements and design constraints for an Unmanned Martian research aircraft based on a tailor-made classical airplane design methodology. First, the exploration mission is described using the information from previous real-world experiences and the desired payload is proposed accordingly. The environmental conditions that dictate severe constraints to the design space are characterized afterwards. The conventional airplane design cycle is modified to address the lack of statistical data and to define a proper design recycling criteria. Eventually, the outcome is presented in the form of a novel configuration that is well suited to carry out the specified... 

Abstract In this study, the response spectrum of a time-varying system such as a beam subjected to moving masses under a harmonic and earthquake support excitations is explored. The excitations are supposed to act on the horizontal directions of the beam axis. The inertial effect of the moving masses on the natural frequencies of the beam for different cases of loading is investigated and a critical value of a so called parameter "mass staying time" is presented to avoid dynamic instability of the system. Finally, some 3D response spectra for different supports excitations as well as the beam natural frequencies are depicted  

This paper presents an optimisation model for polymer electrolyte membrane fuel cell system based on simultaneous power maximisation and cost minimisation. The results show that, by employing appropriate relation between the objectives, the innovative design could be proposed. Genetic algorithm is applied to solve the optimisation problem. Power maximisation results reveal that at maximum amount of power (1.95 kW), unit cost of energy is $0.64. In contrast, minimisation of cost decreases unit cost of energy to $0.33. In this condition, output power is reduced approximately to 0.93 kW. To consider both optimisation problems concurrently, weighting method and Pareto set are employed. Our... 

Metal forming processes are widely used in industrial productions, automobile bodies, food industries, oil refineries, and liquid and gas transmission systems. Analyzing these processes is very important to reduce wastes and optimize the processes. Study of some main factors such as physical and mechanical properties of material and its formability, die geometry, die material, lubrication and pressing speed has been the topic of many research projects. In this paper, forming limit diagrams (FLDs) for LC and ULC steels and the effect of different parameters like the work-hardening exponent, n, and the plastic strain ratio, r, on these diagrams have been evaluated and simulated using... 

In the present paper, a comprehensive study on the prediction of forming limit diagrams (FLDs) for an AA3003-O aluminium alloy is developed theoretically and experimentally. For obtaining the experimental FLDs, an out-of-plane formability test was performed based on the technique proposed by Ozturk and Lee [F. Ozturk, D. Lee, J. Mater. Process. Technol. 170 (2005) 247-253]. The classical Marciniak-Kuczynski (M-K) model and some new yield criteria are utilized to simulate the necking phenomenon and calculate the limit strains theoretically. The employed yield functions are: the BBC2000, BBC2002, and BBC2003 yield criteria proposed by Banabic et al. [D. Banabic, S.D. Comsa, T. Balan, in:...