2018-12-11T11:27:10Z
http://scientiairanica.sharif.edu/?_action=export&rf=summon&issue=345
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
On the orientation dynamics and viscoelasticity of Brownian rigid disklike particles suspended in a shear flow
A.
Moosaie
In this paper, numerical simulations are employed to study the orientation behavior of a dilute suspension of Brownian rigid disklike particles in a simple shear flow. Also, the viscoelasticity of such a suspension is analyzed by considering the stress budget of the two-phase material. A direct Monte-Carlo simulator as well as the moment approximation approaches with two dierent closure models are used to produce the data.Results are compared by available experimental and analytical data, and a very good agreement is established. After the validation of the simulators, the results are presented and discussed. Different Peclet numbers and shape factors of particles are considered and their effects on various quantities are presented, e.g. particle orientations in space, viscous and elastic contributions to the non-Newtonian stress tensor, etc.
Dilute suspension
Rigid disklike particle
Direct Monte-Carlo simulation
Moment approximation
Moment closure model
Brownian motion
2017
06
01
1027
1171
http://scientiairanica.sharif.edu/article_4086_f2bff903af9a658f8339f500d4618cd2.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Feasibility study of a water-to-air heat pipe based heat exchanger for cooling load reduction and energy saving in the office buildings: A simulation study
M.
Ahmadzadehtalatapeh
In the present investigation, the feasibility of cooling load and power consumption effect of a water-to-air heat pipe based heat exchanger (HPHX) on an office building was studied. An oce building in Chabahar Maritime University, in southeast region of Iran, which is considered as a high cooling load demanding region, was chosen as the case study. The present research uses the TRNSYS software to investigate the hourly responses of the existing system added with the water-to-air HPHXs in terms of indoor air conditions and monthly power consumption. The eect of added water-to-air HPHXs on the system was determined, and the results were compared with the existing situation. Water-to-air HPHXs with two, four, and six numbers of rows were examined to recommend the most appropriate conguration for the system. According to the simulation ndings, the existing system with the added six-row water-to-air HPHX is capable of establishing the convenient air into the office space. Moreover, it was shown that by implementation of the six-row water-to-air HPHX, a total amount of 3,108.57 kWh power, which is about 42%, could be saved in a year.
energy consumption
Water-to-air heat pipe based heat exchanger
Indoor air
TRNSYS
2017
06
01
1040
1050
http://scientiairanica.sharif.edu/article_4087_6a5aa5e4074d2ac545779b9ef0740171.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Chaotic behaviors of a ground vehicle oscillating system with passengers
J.
Fakhraei
H.M.
Khanlo
M.
Ghayour
In this paper, some considerations regarding a ground vehicle oscillating system based on chaotic behaviors are studied. The vehicle system is modeled as a full nonlinear seven-degree freedom with an additional degree of freedom for each passenger. Roughness of the road surface is considered as sinusoidal waveforms with time delays for the tires. The governing dierential equations are extracted under Newton-Euler laws andsolved via numerical methods. The dynamic behavior of the system is investigated by special nonlinear techniques such as bifurcation diagram, time series, phase plane portrait, power spectrum, Poincare section, and maximum Lyapunov exponents. The time delays between the tires are used as a control parameter. First, the vehicle behavior is investigated and the chaotic regions are detected. Then, the damping and stiness coecients are used to return to the regular behavior. Results show that by changing the system parameters andselecting the appropriate values, one can minimize vibrations as well as eliminate chaotic behavior. The comparison of the results obtained from the proposed model and those from the vehicle without passengers show the great dierences in the dynamic behaviors of the two models.
Dynamic behavior
Chaotic
Time delay
Vehicle
bifurcation
2017
06
01
1051
1068
http://scientiairanica.sharif.edu/article_4088_711f1351e48d52eb2767468bb317da74.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Effect of wind tunnel wall porosity on the flow around an oscillating airfoil at transonic speeds
A.
Golestani
M.R.
Soltani
M.
Masdari
The effect of porosity in oscillating situations (to the authors' knowledge, for the rst time) on a supercritical airfoil (SC0410) has been experimentally investigated. Tests have been carried out in an open circuit suction-type wind tunnel at a free stream Mach number of M = 0:80. Both static and dynamic (pitching) tests have been carried out on the mentioned airfoil. The oscillation frequency for the unsteady tests has been setto 3 and 6 Hz. The amplitude of frequency is 1 deg. The effect of porosity has been surveyed on the magnitude of pressure uctuations, phase shift, and lift coecient loop. The investigations show that increasing porosity in the test section of transonic regime, contrary to the impression, does not necessarily improve results.
Supercritical
Oscillating
porosity
Transonic
Experimental
2017
06
01
1069
1076
http://scientiairanica.sharif.edu/article_4089_7a9a03c185025d93cf97301c82590880.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
The size-dependent electromechanical instability of double-sided and paddle-type actuators in centrifugal and Casimir force fields
J.
Mokhtari
M.
Farahani
A.
Kanani
R.
Rach
M.
Keivani
M.
Abadyan
The present research is devoted to theoretical study of the pull-in performance of double-sided and paddle-type NEMS actuators fabricated from cylindrical nanowire operating in the Casimir regime and in the presence of the centrifugal force. D'Alembert's principle was used to transform the angular velocity into an equivalent static, centrifugal force. Using the couple stress theory, the constitutive equations of the actuators were derived. The equivalent boundary condition technique was applied to obtain the governing equation of the paddle-type actuator. Three distinct approaches, the Duan-Adomian Method (DAM), Finite Dierence Method (FDM), and Lumped Parameter Model (LPM), were applied to solve the equation of motion of these two actuators. This study demonstrates the influence of various parameters, i.e., the Casimir force, geometriccharacteristics, and the angular speed, on the pull-in performance.
Double-sided nanoactuator
Paddle-type nanoactuator
Angular speed
Cylindrical nanowire
Size henomenon
Casimir regime
2017
06
01
1077
1090
http://scientiairanica.sharif.edu/article_4090_368ac7d3c60fad39a5b29437f2d8a445.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Effects of particle shape and size distribution on particle size-dependent flow strengthening in metal matrix composites
S.
Soleymani Shishvan
A.-H.
Asghari
Effects of particle size on metal matrix composites are studied within the Continuum theory of Mechanism-based Strain Gradient (CMSG) plasticity. This theory has been quite successful in predicting the size-dependent plastic behavior in a wide variety of problems. Two-dimensional (plane-strain) analyses carried out on the composite unit cell models with multi-particles of circular shape show that the flow stress of the composites increases by decreasing particle size with high sensitivity to small particle size. The numerical results are in good agreement with experimental data. Subsequently, the effects of particle shape, orientation, and size distributions on the behavior of composites are investigated. Analyses are carried out on the composites containing squared, rectangular, and elliptical (with aspect ratio of four) particles of various orientations with respect to the loading direction (i.e., vertical, horizontal, and 45 degree inclined directions). The stress inhomogeneity in the matrix, the overall stress-strain curve, and the maximum principle stress in the particles of composites with non-circular particles are investigated and compared with those obtained for the composites containing circular particles. The effects of particle size distribution on the behavior of composites are also addressed.
Particle-reinforced composites
Mechanical properties
Plastic deformation
Modeling
2017
06
01
1091
1099
http://scientiairanica.sharif.edu/article_4091_9561464c249b743d5af11d5ace1981de.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
A reliable implicit difference scheme for treatments of fourth-order fractional sub-diffusion equation
K.
Sayevand
F.
Arjang
In this paper, a reliable implicit dierence scheme is proposed to analyze the fractional fourth-order subdiusion equation on a bounded domain. The time-fractional derivative operator is characterized in the Ji Huan He's sense, and the space derivative is approximated by the ve-point centered formula. The numerical parameters, i.e. consistency, stability, and convergence analyses of the considered scheme, are proven.
Ji Huan He'sn fractional derivative
Convergence
Finite difference approximation
fractional differential equations
stability
2017
06
01
1100
1107
http://scientiairanica.sharif.edu/article_4092_c32973e9f2b7053ec2b6eacd29a69d1c.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Effect of alternating magnetic field on unsteady MHD mixed convection and entropy generation of ferro fluid in a linearly heated two-sided cavity
O.
Ghaffarpasand
This work considers the numerical study of unsteady MHD convection of cobalt-kerosene ferro fluid in a linearly heated two-sided cavity and in the presence of constant and alternating magnetic elds. An accurate nite volume method is adapted to solve the governing equations for this problem. The fluid flow and heat transfercharacteristics are studied for a wide range of Richardson numbers (0:01 Ri 10) and Hartmann numbers (0 Ha 100). The volumetric fraction of nanoscale ferromagnetic particles in ferro fluid also varies between 0:0 0:2, while the size of those nanoparticles is fixed at 45 nm. In addition, different alternating magnetic fields with various periods and phase deviations are utilized to study the effect of time-periodic magnetic field on the flow characteristics and heat transfer. The entropy generation and Bejan number are also evaluated to study the eect of key parameters and temporal variation of magnetic field on various fluid irreversibilities. The results show that applying time-periodic magnetic field has remarkably influenced the fluid characteristics, the fluid irreversibilities, and heat transfer within the cavity. Meanwhile, the influence of phase deviation on heat transfer seems to be insignicant.
MHD mixed convection
Ferro fluid
Two-sided cavity
Linearly heating
Time-periodic magnetic field
2017
06
01
1108
1125
http://scientiairanica.sharif.edu/article_4093_a6b5d9bd363897e6e2838136fe628de1.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Experimental and numerical study on the effect of aluminum foil wrapping on penetration resistance of ceramic tiles
H.
Mazaheri
R.
Naghdabadi
J.
Arghavani
In this work, energy absorption of ceramic tiles wrapped by aluminum foil on its impact face is experimentally and numerically studied. Penetration tests as well as numerical simulations are employed to obtain Ballistic Limit Velocity (BLV) of the tiles. Experimental and numerical results yield BLV of bare tiles as 145 2 and 141.5 m/s, respectively. For the wrapped tiles, these values are increased to 168 2 and 162 m/s, respectively. Therefore, 13% increase in BLV of the ceramic tiles is obtained by just 2.4% increase in its weight. Moreover, it is shown that energy absorption of the wrapped tiles is at least 11% greater than that of the bare ones. Based on the results, the increase in BLV and energy absorption is due to the increase in the fracture conoid angle which postpones crack propagation to the back plate.
Penetration test
Wrapped ceramic tile
Aluminum foil
Ballistic limit velocity
Energy absorption
2017
06
01
1126
1135
http://scientiairanica.sharif.edu/article_4094_9823b7e7ff59ee62c45fece5027da9f9.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Various types of ceramics used in radome: A review
M.
Saeedi Heydari
J.
Ghezavati
M.
Abbasgholipour
B.
Mohammadi Alasti
Advanced tactical missiles need radomes of higher strength capable of withstanding higher velocities and temperatures and longer flight durations. Radomes must be stable at temperature above 1400C and must have a low and steady thermal dielectric constant, low thermal expansion coecient, high resistance to thermal shock, high stiness and strength, high chemical stability, and high resistance against moisture. Silicon nitride, in comparison with other materials used in the fabrication of radomes (e.g., fused Silica, pyroceramics, etc.), enjoys superior properties, and it can also be used at flight speeds higher than Mach 7. In this paper, various types of raw materials used in the fabrication of radomes have been investigated.
Radome
Silicon nitride
dielectric constant
Strength
2017
06
01
1136
1147
http://scientiairanica.sharif.edu/article_4095_858927e7b92549901dceabfb656b5389.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Application of Petrov-Galerkin finite element method to shallow water waves model: Modified Korteweg-de Vries equation
T.
Ak
S.B.G.
Karakoc
A.
Biswas
In this article, modied Korteweg-de Vries (mKdV) equation is solved numerically by using lumped Petrov-Galerkin approach, where weight functions are quadratic and the element shape functions are cubic B-splines. The proposed numerical scheme is tested by applying four test problems including single solitary wave, interaction of two and three solitary waves, and evolution of solitons with the Gaussian initial condition.In order to show the performance of the algorithm, the error norms, L2, L1, and a couple of conserved quantities are computed. For the linear stability analysis of numerical algorithm, Fourier method is also investigated. As a result, the computed results show that the presented numerical scheme is a successful numerical technique for solving the mKdV equation. Therefore, the presented method is preferable to some recent numerical methods.
Modified KdV equation
Petrov-Galerkin method
Shallow Water
Solitary waves
soliton
2017
06
01
1148
1159
http://scientiairanica.sharif.edu/article_4096_e293bc8a63cb5af18bda0924b3a66ea1.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
Numerical simulation of the effect of visitor's movement on bacteria-carrying particles distribution in hospital isolation room
J.
Eslami
A.
Abbassi
M.H.
Saidi
The aim of this paper is to simulate numerically the air flow induced by a walking visitor and its effects on the contaminant transport and ventilation system effectiveness. To this end, the following models will be used in this study: the Lagrangian Discrete Random Walk (DRW) model to trace the motion of BCPs, the dynamic mesh method to simulate the visitor movement, and the Reynolds Averaged Navier-Stokes (RANS) model to solve the air flow. The validation results of the numerical method are in full agreement with the available experimental data in the literature. The findings of the present study indicate that the visitor's movement has remarkable eect on the basic air flow, and the increase of the visitor moving speed can decrease the risk of infection in the AIIR. It is also found that the concentration of BCPs in the back of visitor exceeds10 cfu/m3, and the small distance between the patient and visitor has a negative impact on increasing the BCPs infection of the patient in AIIR. At the same time, it is observed that the effect of walking speed on the ventilation effectiveness index is not remarkable.
Isolation room
Visitor walking
Bacteria transport
Dynamic mesh
Ventilation effectiveness
2017
06
01
1160
1170
http://scientiairanica.sharif.edu/article_4097_28083fb82566825d5ed3279891b604cf.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
3
A new technique of the first and second limits" for wagon maintenance in railway tracks consisting of sharp curves based on the empirical study of wheel wear
S.M.
Salehi
G.H.
Farrahi
S.
Sohrabpour
Wheel wear is one of the major costs in railway tracks consisting of sharp curves. In this paper, wear behavior of S1002 proles of wheels in the Southern Line" of Iran's railway, which consists of a large number of distinct and/or consecutive sharp curves, is studied using the field data measuring technique. Based on wear behavior analysis of all wheels, an optimal wagon maintenance technique called the first and second limits" is suggested to minimize the wagon's cost per traveled distance. The results show that:1) A severe wheel flange wear occurs for all wheels in comparison to the wheel tread wear in normal tracks; 2) A wagon's detachment for repair of critical wheels on its four axles occurs at the traveled distances of 40,000 km, 54000 km, 71000 km, and 75000 km, respectively (much less than the normal traveled distance of 500,000 km); 3) A fifth order polynomial function can be appropriated to represent the wear behavior of the wheels;4) By implementing the suggested technique, the cost per traveled distance decreases by 38.64%, and the travelled distance increases by 45%.
Wheel wear
Maintenance technique
sharp curves
Empirical study
Wheel longevity enhancement
Wheel flange wear behavior
Wagon's maintenance cost enhancement
2017
06
01
1171
1180
http://scientiairanica.sharif.edu/article_4098_61cb7727b18e1f818b02572664293f3a.pdf