Scientia Iranica
Volume:24 Issue: 3, 2017

In this study, numerical simulations are employed to study the orientational bahevior of a dilute suspension of Brownian rigid disklike particles in a simple shear flow. Also, the viscoelasticity of such suspension is analyzed by looking at the stress budget of the two-phase material. A direct Monte-Carlo simulator as well as the moment approximation approaches with two different closure models are used to produce the data. The results are compared by available experimental and analytical data and a very good agreement is established. After the validation of the simulators, the different results are discussed. Different P''eclet numbers and shape factors of particles are considered and various results are presented, e.g. particle orientations in space, viscous and elastic contributions to the non-Newtonian stress tensor, etc.

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 office 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 effect 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 configuration to the system. According to the simulation findings, 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.

Abstract 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 degrees of freedom with an additional degree of freedom for each passenger. Roughness of the road surface is considered as sinusoidal waveforms with a time delay for the tires. The governing differential equations are extracted under Newton-Euler laws and are solved 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, Poincaré section, and maximum Lyapunov exponents. The time delays between the tiresare used as a control parameter.First, the vehicle behavior is investigated and the chaotic regions are detected. Then, the damping and stiffness coefficients are used to return to the regular behavior.Results show that by changing the system parameters and selecting the appropriate values one can minimize vibrations, as well as eliminating chaotic behavior. The comparison of the results obtained from the proposed model and those from the vehicle without passengers show the great differences in the dynamic behaviors of two models.

The effect of porosity in oscillating situations (to the authors’ knowledge, for the first 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=0.801. Both static and dynamic (pitching) tests have been carried out on the mentioned airfoil. The oscillation frequency for the unsteady tests has been set to 3 and 6 Hz. The amplitude of frequency is 1 deg. The effect of porosity has been surveyed on the magnitude of pressure fluctuations, phase shift and lift coefficient ring. The investigations show that increasing porosity in the test section of transonic regime, contrary to the impression does not improve results necessarily.

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 Di erence Method (FDM), and Lumped Parameter Model (LPM), were applied to solve the equation of motion of these two actuators. This study demonstrates the in uence of various parameters, i.e., the Casimir force, geometric characteristics, and the angular speed, on the pull-in performance.

Particle size effects in 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 which are 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 a 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 distribution 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.

In this paper, a reliable implicit difference scheme is proposed for analyzing the fractional fourth order sub-diffusion 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 means of the five points centered formula. The numerical parameters, i.e., consistency, stability and convergence analysis of the considered scheme is proven.

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 BLVof 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.

Advanced tactical missiles need radomes of higher strength capable of withstanding higher velocities and temperatures and longer ight 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 sti ness 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.

In this article a Petrov-Galerkin method in which the element shape functions are cubic and weight functions are quadratic B-splines, is introduced to solve the modified Korteweg-de Vries (mKdV) equation. Solitary wave motion, interaction of two and three solitary waves and the development of the Gaussian initial condition into solitary waves are studied using the proposed method. Accuracy and efficiency of the method are demonstrated by computing the numerical conserved laws and $L_{2}$, $L_{infty }$ error norms. The computed results show that the present scheme is a successful numerical technique for solving the mKdV equation. A linear stability analysis based on the Fourier method is also investigated.

Visitors’ movement and shedding bacteria-carrying particles (BCPs) from their bodies are both the most important parameters which may influence the airflow field and the induced contaminant dispersion in airborne infection isolation room (AIIR). The aim of this paper is to simulate numerically the airflow induced by a visitor walking and its effects on the contaminant transport and ventilation system effectiveness. To this end, the following will be used in this numerical simulation: the Lagrangian discrete method to trace the motion of BCPs, the dynamic mesh method to simulate the visitor movement, the Eulerian RANS model to solve the airflow. The validation results of the numerical method were in full agreement with the available experimental data in the literature. The findings of the present study indicate that the visitor’s movement has a remarkable effect on the basic airflow,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 exceeds 10 CFU/m3 and the small distance between the patient and visitor has a negative impact on increasing the BCPs infection of patient in AIIR. At the same time, it is observed that the effect of walking speed on the ventilation effectiveness index is not remarkable. Finally, the results of the present study demonstrate that the visitor’s movement plays a decisive role to increase the infection risk around the patient therefore more in-depth investigations needs to be carried out in the future.

Wheel wear is one of the major costs in railway tracks consisting of sharp curves. In this paper wear behavior of the S1002 profiles 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 “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 decreased by 38. 64%, and the travelled distance increased by 45%.

This work concerns with the numerical study of unsteady MHD convection of cobalt-kerosene ferrouid in a linearly heated two-sided cavity and in the presence of constant and alternating magnetic field. An accurate finite volume method is adapted to solve the governing equations for this problem. The fluid flow and heat transfer characteristics are studied for a wide range of Richardson number (0.01