Iranian Journal of Mechanical Engineering Transactions of ISME
Volume:23 Issue: 1, Mar 2022

In this study, residual stresses in a finite sample separated from the seam-weld of an API pipe with a large diameter were studied for the first time. A finite element simulation of the welding process was conducted to achieve a safe dimension for this sample. After validation of the results, residual stresses were obtained in different directions in this way. Residual stress distribution in the thickness direction represented for the first time is important; firstly, based on standards the accuracy of central-hole-drilling results depends on it. Secondly, this distribution sheds light on the 3D equilibrium of residual stresses. The results show that a finite sample with the size of 320×440 mm separated from the main pipe is appropriate for doing the central-hole-drilling test which is a significant achievement. It is also proved that the maximum value of residual stresses takes place on surfaces of the sample, while the minimum of this figure was reported in the middle of the thickness. This achievement ensures that the maximum and critical values of residual stresses are obtained by the CHD technique.

New alloys of aluminum piston alloy made by adding more nickel to their usual composition. Bulk-forming of new alloys at ambient temperature by conventional methods is not possible. Therefore, the hot-compression deformation behavior of these alloys has been studied in this study. Based on the true stress-strain graphs obtained from the experiments, the constitutive model proposed for these alloys based on the Johnson-Cook model. Then this model is improved by considering the coupled effects of the parameters. The accuracy of the proposed models has been investigated using appropriate statistical analysis, and as a result, the accuracy of the presented models has been confirmed. The modified model, compared to original model, in addition to the higher accuracy, can predict the trend of changes in flow stress. The study of variations of the model coefficients shows that with an increasing nickel content in the alloy composition, the strength and the flow stress of the alloys increased intensely at all temperatures and strain rates. Also, by increasing the amount of nickel, the effect of the strain rate on flow stress is reduced.

In this work, finite difference method is applied to two-dimensional transient heat and mass transfer of Casson nanofluid past an isothermal vertical conical plate embedded in a porous media under the influences of thermal radiation and magnetic field. The results of the numerical computations and simulations show that the temperature and concentration of the fluid increase as the Casson fluid and radiation parameters as well as Prandtl and Schmidt numbers increase. As the Grashof number, radiation, buoyancy ratio and flow medium porosity parameters increase, the velocity of the Casson fluid increases. However, it was recorded that the Casson fluid parameter, buoyancy ratio parameter, the Hartmann, Schmidt and Prandtl numbers decrease as the velocity of the flow increases. Also, the time to reach the steady state concentration, the transient velocity, Nusselt number and the local skin-friction decrease as the buoyancy ratio parameter and Schmidt number increase. Further investigations depict that the steady-state temperature and velocity decrease as the buoyancy ratio parameter and Schmidt number increase. Additionally, the results depict the local skin friction, Nusselt and Sherwood numbers decrease as the Schmidt number increases. Though, the local Nusselt number increases as the buoyancy ratio parameter increases. It was established that near the leading edge of the plate, the local Nusselt number is not affected by both buoyancy ratio parameter and Schmidt number.

This study aims to achieve effective analysis and fast modeling in free vibration and flutter analyses of low aspect ratio composite wings in subsonic flow for the preliminary design stage instead of using the computationally expensive finite element method. It uses an equivalent plate method for structural modeling. Also, it uses the doublet point and the U-g methods for calculation of unsteady aerodynamic loads and carrying out flutter analysis, respectively. We investigate the effects of different parameters on the flutter behavior. The present results confirm that the structural tailoring can make a harmonious balance to the wing sweep angle effect upon the flutter behavior of composite wings, and a considerable improvement upon flutter performance is achieved by using composite materials.

The modeling of solar stills using CFD is a quick and low-cost way of designing and optimizing these systems. So far, only basin-type solar stills have been numerically analyzed; and it is the first time that a 3-D stepped solar still model has been numerically analyzed in the present work. A 3-D and 3-phase numerical model of a stepped solar still is presented in this research. The exterior of this solar still is exposed to ambient temperature and pressure. The initial conditions and temperatures of the system have been determined by an experimental test. The validation results of the present numerical model have a good agreement with former empirical results. The amount of error between numerical and empirical results varies at different times of the day. At early hours, the difference between the water temperatures obtained by modeling and by experimentation is only 1.6%, which rises to 11.7% at later hours of the day. This amount of discrepancy is due to the change that occurs in the behavior of solar still under ambient conditions.

In the current study, an operational method for feasibility study of aphotovoltaic powerplant connected to the grid with total capacity of 1MWprovide. This method first uses the geographical conditions of thepowerplant’s location to determine the arrangement for photovoltaicarrays with the conditions of minimized space use and suitable distancebetween photovoltaic strings to facilitate maintenance and repair andpreventing modules from casting shadows on each other. The innovationof the current article is using the empirical data to compare the simulatedpowerplant and an actual powerplant from economic, performance andenvironmental pollutant aspects. The error analysis between the actualpowerplant and simulated model is used to determine the accuracy of thesimulation results. Furthermore, the amount of CO2 emission reductiondue to the construction of this powerplant is investigated. The resultsindicated the importance of the geographical location and indicated whichlocations in Iran provide the highest efficiency for construction ofphotovoltaic powerplants. Furthermore, the other innovation is todetermine the number of residential apartment units whose electricity wasprovided by this powerplant.

Environmental pollutants such as soot, nitrogen oxides, and carbon monoxide are the main demerits of fossil fuels. Therefore, it is imperative to control the air pollutants in order to provide a clean and pleasant environment. In the present study, the effects of temperature, mass flow rate of the injected fuel, pore diameter, porosity and ambient pressure on the amount of pollutants are investigated in the combustion chamber. The combustion process is numerically simulated by employing Species Model at species transport mode of operation. Discrete Phase Model is used to predict flow field behavior by considering the interaction between liquid and gas phases. Also, the flow is simulated under turbulent regime with the diffusive flame in the combustion process. Results show that increasing the heat transfer in porous medium leads to the decrease in the gas temperature and NOX formation. The production of unburnt hydrocarbon species like carbon monoxide decreases due to a better pre-heating process in the porous medium. Increasing the diameter of pores slightly reduces the amount of carbon monoxide, while the amount of nitrogen monoxide surges up.