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Showing 3 results for Mojaddam
Volume 1, Issue 1 (Spring and Summer 2024)
Abstract
Edrisid, as the first Alawite state in the second half of the second century A.H, settled down in North-West Africa; in a region surrounded by hostile states from all sides, the Umayyads of Andalusia in the north, the Aghlabid's in the east; and the Banurostam government in the northeast and Banumedarar government in the southwest. Being located in such a geographical position must lead to the inevitable entry into long and erosive wars and endless tensions. However, by studying the history of Edrisid's not only don’t we see any continuous wars but we come across a stable government which carries out the most brilliant period of civilization in the Islamic Maghreb region in the first centuries (A.H.). The current research intends to look into Edrisid's foreign policy management and explaining the strategies of this government in curbing hostilities and turning crises into opportunities in the field of diplomacy. Data analysis in the historical reports related to this government reveals that the Edrisid's were able to succeed in foreign policy by adopting policies such as: religious tolerance, extensive business relations with neighbors, establishment of a balance of power and exploiting tribal differences in the territory of neighbors. Through these measures, they were able to avoid erosive conflicts and continuous wars with neighbors and thus provide the basis for stability and development in their territory.
Seyyed Mohammad Sajad Seifi, Mohammad Mojaddam, Pouyan Hashemi Tari,
Volume 18, Issue 9 (12-2018)
Abstract
Aerodynamic and optimal design of a blade of a horizontal axis wind turbine (HAWT) has been performed in order to extract maximum power output with considering the strength of the blade structure resulted from different loads and moments. A design procedure is developed based on the Blade Element Momentum (BEM) theory and suitable correction factors are implemented to include three-dimensionality effects on the turbine performance. The design process has been modified to achieve the maximum power by searching an optimal chord distribution along the blade. Based on the aerodynamic design, the blade loads have been extracted and the blade mechanical strength has been investigated by analyzing the thickness of the blade surface and the blade material. The developed numerical model can be considered as a suitable tool for aerodynamically and mechanically design of a turbine blade. The results for a 500 W turbine show that the turbine performance improves by 5% approximately, by modifying chord radial distribution. Yield stress analysis shows the effect of introduced chord distribution on the blade strength, in different blade thicknesses and different blade materials. In addition, optimum tip speed ratio for having favorable mechanical safety factor is derived. Three different airfoil are examined for this investigation and comparing their mechanical safety factor.
Seyed Morteza Sajadmanesh, Mohammad Mojaddam, Arman Mohseni,
Volume 19, Issue 10 (October 2019)
Abstract
Turbofan engines are widely used in modern aircraft. Low-pressure turbines are the heaviest components of turbofan engines, and reduction of their weights is very effective in improving the specific fuel consumption and overall efficiency of these engines. One of the methods of decreasing the engine weight is to decrease the number of blades which is accompanied by an increase of the blade loading. For this purpose, high-lift airfoils can be used. As the occurrence of flow separation is very probable in high-lift blades, the recognition of the location and size of the separation bubble is important to assess the energy loss of flow. In this research, T106D-EIZ high-lift cascade is simulated by two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with Shear Stress Transport (SST) turbulence model and γ-Re_θ transition model in two Reynolds numbers 200,000 and 60,000 at a constant isentropic exit Mach number of 0.4, which represent a typical flow condition in low-pressure turbine. The results show that when Reynolds number is high, the separation bubble remains small on the suction side and the separated shear layer returns to the blade surface, and the energy loss of flow decreases. On the other hand, at a low Reynolds number, the separation bubble grows and energy loss increases. Separation bubble is not directly detectable in an evaluation of pressure distribution. However, proper orthogonal decomposition of the pressure field provides the capability to identify flow structures including vortex stretching, the onset of flow separation, and flow reattachment. When the separation bubble is long, large vortical structures are formed on the suction surface. Release of these large vortices can increase the profile loss by more than 50 percent.
