2020-12-05T09:29:40Z
http://scientiairanica.sharif.edu/?_action=export&rf=summon&issue=294
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Simulations of Particle Filtration and Tracking in Electrical Field
Ahmad
Sedaghat
Amir Hossein
Mohammadzadeh
The movement of charged particles in an electrical field is of practical importance in filtration efficiency and in electrostatic coating. In this paper, both of the applications have been investigated computationally. For the case of filtration, a mathematical model is introduced for the electret filter which is made of split type fibers. The filter was assumed to be composed of rectangular fibers arranged in staggered array field. Simulation was conducted to study the filtration efficiency. Single fiber efficiencies under various filtration conditions were calculated and compared with results obtained from semi-empirical expressions. In the electrostatic powder painting, the gas flow and particle flow fields inside a coating booth under given operating conditions are considered and the effects of particle sizes on their trajectories are studied. Steady state turbulent gas flow was simulated by solving incompressible Navier–Stokes equations and the standard k−ε turbulence model. The discrete phase of particles was modeled based on the Lagrangian approach. In both cases studied here, the flow field and the collection mechanisms were accurately simulated experimental observations.
Particle/gas flow
numerical simulation
Electrical filter
Powder coating
2014
02
01
109
118
http://scientiairanica.sharif.edu/article_3474_35e45f539e39f60047fe99653fb68cfe.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Numerical simulation of oblique impact of a droplet on a surface in the film boiling regime
P.
Pournaderi
A. R.
Pishevar
In this study we focused on the simulation of oblique collision of a water droplet on a superheated surface via a novel algorithm. In this approach vaporization rate of the droplet is computed and is accurately applied in the solution process. High temperature of the surface leads to the formation of a vapor layer between droplet and surface. Mesh clustering near the surface is used to capture the effect of the vapor layer. The level set method in conjunction with the ghost fluid method is used to represent a sharp interface. Available experiments confirmed the validity of the proposed algorithm. The Weber number based on the normal velocity is the dominant parameter in the oblique impact process. Spreading radius and contact time of the droplet are dependent on the normal Weber number. An increase in the initial normal velocity of the droplet enhances the total heat removal from the wall.
oblique impact
Leidenfrost regime
droplet
hot surface
level set
ghost fluid method
2014
02
01
119
129
http://scientiairanica.sharif.edu/article_3475_b7e8ee0f67f29711c3739a82e2d18fd1.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
The Effect of Angle of Attack on Limit Cycle Oscillations for High-Aspect-Ratio Wings
Morteza
Dardel
Keivan
Eskandary
Mohammad Hadi
Pashaei
Amir Hossein
Kiaeian Moosavi
In this study, the effect of the angle of attack on aeroelastic characteristics of high aspect ratio wing models with structural nonlinearities in unsteady subsonic aerodynamics flows are investigated. The studied wing model is a cantilever wing with flag, lag and torsion vibrations and with large deflection capability in according to Hodges-Dowell wing model. An unsteady low speed incompressible air flow is assumed to include the flow time lags. Variation of the limit cycle amplitudes and frequency with free stream velocity in different angle of attacks are carefully studied. For considered model, angle of attack has little effect on flutter velocity but its effect on limit cycle amplitudes and frequency is considerable. This study shows that the limit cycle amplitudes are very sensitive to variations in angle of attacks.
High aspect ratio wing
flap-lag and torsion
angle of attack
flutter
limit cycle oscillation
2014
02
01
130
146
http://scientiairanica.sharif.edu/article_3476_c33e649be4d50d6a6b366203152ccd4e.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Modified fixed-grid finite element method in shape optimization problems based on gradientless method
M.
Heshmati
F.
Daneshmand
Y.
Amini
This paper presents a methodology for solving shape optimization problemswhere the unknown is the shape of the problem domain. The proposed algorithm is based on the minimization of the stress along design boundary calculated by the Modified Fixed Grid Finite Element Method (MFGFEM).
Using MFGFEM eliminates mesh adaptation and re-meshing processes as needed in the standard finite element method and reduces the analysis cost significantly. In this study, a new approach for computing stiffness matrix of boundary intersecting elements is also presented and optimal shape of the problem domain is obtained via a simple optimization algorithm.The performance of the proposed approach is investigated for the shape optimization problems. It is concluded that the results of the present method are in a good agreement with other analytical and finite element solutions.
Shape optimization
Fixed-grid finite element method
gradientless method
Stress concentration
2014
02
01
147
161
http://scientiairanica.sharif.edu/article_3477_140fe1a51edf2b55873c74336b63bcef.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Tribological Investigation of RBD Palm Olein in Different Sliding Speeds using Pin-on-disk Tribotester
S.
Syahrullail
M.I.
Izhan
A.K.
Mohammed Rafiq
The tribological investigation in term of coefficient of friction and wear resistance of refined, bleached and deodorized palm olein was conducted using a pin-on-disk tribotester. Palm oil was selected as a candidate due to its superior tribological properties and its large production, that can lead to the mass production of bio-lubricant. The material of the pin and the disk is Titanium (Ti6Al4V).The experiments were conducted following the ASTM G99. The normal load was 9.8N and the observation time was 1 hour. The sliding speeds were 0.25m/s and 1m/s. In this research, only 5ml of the test lubricant was applied at the beginning of the experiment to investigate the capability of the lubricant to maintain its function. To make sure the lubricant do not subside due to the centrifugal force from the rotating disk, a groove was crafted on the disk. In this research, coefficient of friction and wear rate were calculated. From the analyses, the coefficient of friction calculated for palm olein was the lowest for both sliding speed conditions, while the wear rate obtained showed that palm olein was an efficient lubricating oil at a low speed and had high wear rate obtained at the high speed.
pin-on-disk
palm olein
wear rate
coefficient of friction
sliding speed
2014
02
01
162
170
http://scientiairanica.sharif.edu/article_3478_149ceb755cd6f2f8356b3c675adad2ab.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Effect of speed and load on exergy recovery in a water-cooled two stroke gasoline-ethanol engine for the bsfc reduction purposes
M.
Ghazikhani
M.
Hatami
B.
Safari
Most important part of the second law of thermodynamic is described as determining the value and sources of wasting exergy in processes and suggests concepts for reducing the losses in order to enhance the efficiency. So, the main purpose of this paper is to study the effect of alcoholic additives and load and engine speed on combustion irreversibilities and second law efficiency. The mentioned alcoholic fuel is Ethanol which is combined with gasoline in different percentages of 5, 10, and 15%. The experiments have been done for 2500, 3000, 3500 and 4500 rpm and 25%, 50% and 75% full load. The results show that in most of the times that the alcoholic fuel was used, the combustion internal irreversibility increased and second law efficiency decreased, which is due to the increase in temperature difference between burnedcombustionproductsand unburned mixture, but increasing in load and engine speeds, increased the second law efficiency. Another important outcome from present study is demonstrating the brake specific fuel consumption (bsfc) reduction due to using recovered exergy from water which its average value was 14.1%.
Exergy
Irreversibility
Two Stroke Engine
Ethanol
bsfc
2014
02
01
171
180
http://scientiairanica.sharif.edu/article_3479_fb0f8ea8ced2dae6745e0c156d94959a.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Machining commands generation with the rotational C2 PHquintic curve interpolant for cam profile manufacturing
Javad
Jahanpour
Hossein
Dolatabadi
This paper presents a new method to generate the cam position commands required for manufacturing a cam profile by an open-architecture CNCmachine. At first, the junction points of several connected PH quintic curves as the cam segments are obtained based on the supposed desired follower motion. Consequently, the desired cam curve is represented via multi-segment C2 PH quintic curve. After that, the new interpolation algorithm is proposed to generate the position commands required for machining of the cam. The designed cam-follower mechanism is performed for several case studies to evaluate the effectiveness of the employed curve representation and the proposed interpolation algorithm. The simulation results demonstrate that the proposed interpolation algorithm is capable for providing a smooth transition for all regions of the follower motion and the obtaineddisplacement, velocity, acceleration and jerk profiles match the corresponding desired profiles closely. Therefore, the newly advised interpolation algorithm with the uniform segmentation scheme is not only feasible for generating the cam position commands but also yields satisfactory performance for the follower motion. Also, the non-uniform rotational segmentation of the cam curve causes the amount of the kinematic characteristics of the follower motion are significantly increased compared to the corresponding desired profiles.
Cam profile
C2 PH quintic curve
Junction point
Rotational interpolation
CNC command generation
2014
02
01
181
191
http://scientiairanica.sharif.edu/article_3480_ba9fdeb6a00669a237bdce925040fb2f.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
The Unsteady Behavior of Subsonic Wind Tunnel Wall Pressure during a Pitching Motion of the Model
Ali R.
Davari
M. R.
Soltani
M.
Ghaeminasab
Extensive low speed wind tunnel experiments have been undertaken to measure the test section floor wall pressure distribution in presence of a 2D wing inside the test section. The experiments were performed for both static and dynamic pitching motion of the model at different conditions. In these measurements the effects of existence and oscillations of 2D wing on the floor wall pressure at various locations were studied. According to the results, as the oscillation parameters such as mean angle of attack and frequency change, the wall pressure at the points located in the front part of the test section, in the upstream region, exhibit a different behavior than those in the downstream part. Viscosity is shown to be a major contributor in convecting the fluctuations caused by the model oscillations to the flowfield. As the Reynolds number increases, the downstream region receives less disturbances from the pure dynamic motion of the model. It is believed that the static wake is the dominant contributor in the absence of the viscous effects.
Interference Effect- Pitching Oscillation- Reduced Frequency- Upstream- Disturbance Convection
2014
02
01
192
202
http://scientiairanica.sharif.edu/article_3481_b684bbd593480b5f9497e3d862d60c88.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Magnetohydrodynamic flow in a permeable channel filled with nanofluid
M.
Sheikholeslami
D.
D. Ganji
In this paper, the problem of laminar Magnetohydrodynamic nanofluid flow in a porous channel is investigated. Optimal Homotopy Asymptotic Method (OHAM) is used to solve this problem.In order to consume CPU time, Galerkin method is used to minimize the residual. This investigation compared with numerical method (four-order Rung-kutte method) and found to be in excellent agreement. The base fluid in the channel is water containing copper as nanoparticle. The effective thermal conductivity and viscosity of nanofluid are calculated by the Maxwell–Garnetts (MG) and Brinkman models, respectively. The influence of the three dimensionless numbers: the nanofluid volume fraction, Hartmann number and the Reynolds number are examined. The results indicate that velocity boundary layer thickness decreases with increase of Reynolds number and nanoparticle volume fraction and it increases as Hartmann number increases.
Nanofluid
Laminar flow
Permeable channel
Uniform magnetic
Optimal Homotopy Asymptotic Method (OHAM)
galerkin method
2014
02
01
203
212
http://scientiairanica.sharif.edu/article_3482_f3cf86f183452192313c202b51a09d74.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Mathematical Modeling and Decomposition of Hydrodynamics-Acoustic Fields Using Perturbation Methods
Mohammad
Riahi
Norouz M.
Nouri
Ali
Valipour
Conservation of mass, momentum, energy and state equations are recognized as basic mathematical models in the analysis of acoustic behavior of cavitation as well as supercavitation. Also, it is known that the order of acoustics effects aren’t as higher as hydrodynamics ones. Therefore, in this paper, initially, for comparing different terms of equations, via using scale analysis, conservation equations are converted into dimensionless. Then by comparing all conditions coupled with weighting terms available in those equations, groups of parameter which are most appropriate with the hydrodynamics and hydroacoustic of the cavitating flow were selected. By regarding acoustic as lower order phenomenon, compared to hydrodynamic of flow and simultaneously using perturbation method, two equations containing leading and first orders and different terms could be attained. Obtained results were indicated that leading order equations represent hydrodynamic of the cavitating flow and first order equations indicate acoustics of cavitation or supercavitation. Acoustic equations of the present study contain terms related to fluid viscosity, density and pressure changes and background flow velocity. As acoustic equations coupled with leading order equations, in order to find noise of cavitation, equations of fluid flow for compressible flow should be resolved.
Mathematics Modeling
Cavitation
Supercavitation
Perturbation method
Scale Analysis
2014
02
01
213
221
http://scientiairanica.sharif.edu/article_3483_41fe54f78c84ec32e18ab89f99a4ba3a.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Performance Study on Dehumidifier of Packed bed Liquid desiccant System
Hesamoddin
Salarian
Bahram
Ghorbani
Majid
Amidpour
Gholamreza
Salehi
Liquid desiccant evaporation cooling air conditioning system introduced in this paper. The dehumidifier and regenerator play the most important role in this system. For liquid-gas contact, packed towers with low pressure drop provide good heat and mass transfer characteristics for compact designs.The experimental data have been obtained from a built prototype of liquid desiccant system in a packed bed unit with a surface area per unit volume ratio of 125 m2/m3, the liquid desiccant ,viz lithium chloride. The result showed that the mean mass transfer coefficient of the packing dehumidifier was 0.02kg/ m2s Also the absorber characteristic parameter, the packing size or number of transfer units (NTU), and air-to-desiccant solution mass flow rate ratio (ASMR) are crucial parameters. These parameters are affected to humidity effectiveness and enthalpy efficiency, are introduced and defined in this paper. High efficiency could be achieved if proper values of these variables are selected. In this studyenthalpy efficiency from experimental results has been comparedwith theanalytical computation result based on optimumASMR. From analytical solution, an optimum mass flow rate ratio can be deduced for optimal design of both dehumidifiers and regenerators, but in this studybehavior of the absorberhas been considered.
liquid desiccant system
absorber
Experimental model
dehumidifier efficiency
mass transfer coefficient
optimumASMR
2014
02
01
222
228
http://scientiairanica.sharif.edu/article_3484_6fb625792bee477fe28dc4388bdf5a68.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2014
21
1
Analytical solution for the generalized Kuramoto-Sivashinsky equation by differential transform method
Saeideh
Hesam
Alireza
Nazemi
Ahmad
Haghbin
In this paper, the numerical solution of the generalized Kuramoto-Sivashinsky equation is presented by differential transform method (DTM). The DTM is a powerful and efficient technique for nding solutions of nonlinear equations without the need of a linearization process. In this approach the solution is found in the form of a rapidly convergent series with easily computed components. Numerical experiments demonstrate accuracy and robustness of the method for solving a class of onlinear partial differential equations.
Kuramoto-Sivashinsky equation
Differential transform method
exact solution
Closed form solution
2014
02
01
229
229
http://scientiairanica.sharif.edu/article_3485_f0e7f08a6c45f6e2afb58d8b3b276c67.pdf