نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و چهارم شماره 3 (پاییز 1401)

This paper studied the oxygen flow distribution in a PEM fuel cell stack numerically. At first, the flow in the stack was simulated as a single phase, and the effect of gradual reduction of manifold height (tapered manifold) on improving the flow distribution between fuel cells was investigated. Standard deviation and non-uniformity coefficient have been used to measure the flow maldistribution. Gradual reduction of manifold height up to 70% in the tapered manifold improved standard deviation and non-uniformity coefficient by 6.9% and 8.4%, respectively. The results of the two-phase simulation showed that the condensation of water vapor in the saturated oxygen could cause the accumulation of liquid water at the end of the manifold. As the smaller droplets merged, the droplet radius formed at the end of the manifold increased until it detached from the manifold wall and entered the last cells. Less liquid water entered the last cell at shorter intervals in the tapered manifold. It was suggested that by creating a water chamber at the end of the manifold, condensed water be collected from the manifold and discharged from the stack. Increasing the mass flow at the manifold inlet and discharging the excess gas through the water collection chamber can push the liquid water into the chamber without causing significant changes in pressure drop.

Composite Lattice structures are one of the most widely used structures in the aerospace industry in recent years. These structures are composed of a large number of oblique and circumferential ribs with specific distances from each other and in addition to strength, they are very light in terms of weight. The present study includes an analytical expression and a solution to the problem of free vibrations of a composite lattice cylindrical shell. The continuous formula for calculating the natural frequency of a cylindrical lattice structure was obtained by considering the Winkler-Pasternak elastic foundation from the governing equations of the shell based on Galerkin methods. This formula, in addition to being used to estimate the frequency in the initial design phase, is also a tool for evaluating the vibration analysis of composite lattice shells in mechanical analysis. The results have been calculated analytically in two cases with and without elastic foundation and the accuracy of the results has been confirmed by finite element modeling. For finite element method simulations, Winkler and Pasternak coefficients have been replaced by shear and radial springs, respectively. The natural base frequency of the system depends on the properties of the elastic substrate, so changing the stiffness of the radial and shear springs causes a change in the natural frequencies.

In the present work the amount of entropy produced due to the conjugate heat transfer of power-law fluids during natural convection within the inclined chamber under magnetic field and heat absorption/production is investigated. Outcomes:1-The flow power,the amount of heat transfer and the entropy produced decrease with increasing Hartmann number, decreasing Rayleigh number and increasing the fluid power-law index.2-As the power-law index decreases,the influence of the magnetic field becomes more pronounced.The mean Nusselt number decreases by about 52% for shear thinning fluid and by about 18% for dilatant fluid by increasing the Hartmann number to the highest value.3-To achieve a current with higher power and higher average Nusselt number,the magnetic field can be used non-uniformly,especially TMF1. The larger the Hartmann number, the more pronounced the change in the type of magnetic field applied.The influence of the change in the type of magnetic field applied to the shear thickening fluid is minimal.4-As the thermal conductivity ratio increases, the maximum mean Nusselt number is obtained, in which case the impact of increasing the Hartmann number and the Rayleigh number becomes more pronounced.5-The minimum amount of heat transfer, current strength and magnetic field influence is obtained when the chamber is at an angle of +90 degrees,in which case the average Nusselt number is up to about 82% less than the zero angle.6-The Bejan number increases with increment of heat absorption/production coefficient,increasing Hartmann number, decreasing Rayleigh number and decrement of thermal conductivity ratio,and maximum the Bejan number is obtained at an angle of +90 degrees.

In this paper, the effect of geometry and addition of aluminum foam adsorbents on the energy absorption of nested thin-walled profiles under compressive axial load is investigated. ABAQUS commercial finite element software has been used for numerical analysis. The nested profiles are made of 6060-T5 aluminum material and the outer and inner profiles are considered with circular, square, hexagonal and octagonal cross sections. Force and displacement diagrams have been used to study the energy absorption rate of different nested geometries along with the calculation of total energy absorption and specific energy absorption. Finally, in order to investigate the effect of adding metal foam, three modes of adding aluminum foam to the nested profile under axial load were investigated. Nested thin-walled profiles absorb more energy when the foam is added than when hollow. In addition, the interaction between the foam walls and the pipe causes an additional increase in energy dissipation.

The comfort of car passengers is one of the most important issues while driving, therefore the suspension system plays a significant role in this matter. To investigate this issue, in this research, the design of a fault-tolerant control system for the active suspension system of the one half- car model has been considered. In this article, the goal is to design a robust-adaptive sliding mode controller to stabilize the vehicle suspension system and converge the output response to the desired response. For this purpose, firstly, the model of the suspension system of the one half of the car is considered in the presence of actuator, sensor, modeling uncertainties and limited external disturbances. Then, with the assumption of not knowing the upper band of the term, including system faults and disturbances, the error tolerant control law has been designed so that the output response of the system in front of any sudden fault converges to the desired(stable) value and also the output of a desired path.

In this study, the effect of replacing the elastic wall in a two-dimensional channel for forced convection flow around a circular cylinder surrounded by an incompressible flow has been studied numerically. As the current passes around the hot cylinder and the elastic wall oscillates, the rate of heat transfer changes at any time, which is a function of the vibration conditions of the elastic oscillator. Amplitude, frequency and vibration mode are the main parameters affecting the current passing through the channel. The2refore, in this study, the effect of oscillator vibration in the first, second and third modes has been investigated and in each mode, three different amplitudes and in each amplitude three different frequencies have been investigated and the calculations for two Reynolds numbers 100 and 200 have been solved. Rigid channels are compared. The results show that in the first mode, unlike the second and third modes, the elastic wall oscillation has a great effect on the average Nusselt number, average output temperature and cylinder drag coefficient. in all modes, with increasing amplitude and frequency, the average Nusselt number, the average output temperature and the drag coefficient of the cylinder increase.