فهرست مطالب جاماسب پیرکندی

In present research the combustion process of solid fuel ramjet(SFRJ) was modeled in numerical state. Different five geometrical cases were employed for parametric study of back step height and aft-combustor length effects on propulsion properties in this numerical model. Results showed less than 10 percentage error in compare with reference data. Extracted numerical data from this research show decreasing burning rate, increasing combustion efficiency and thrust force due to increasing the step height also decreasing combustion efficiency and thrust force as results of decreasing the aft-combustor length. The results demonstrate that variation of the aft-combustor length hasn’t sensible effect on burning rate also optimum value for specific impulse occur when dimensionless aft-combustor length is equal to 0.95.

In this paper, the effect of negative Poisson's ratio on the mechanical response and improving the damage behavior of carbon/epoxy composite laminates under low-velocity impact is studied. For this purpose, a MATLAB code is developed to determine the range of sequence angles to achieve both negative Poisson's ratio in-plane and through-thickness based on CLT. Also, the progressive damage model is written and implemented using the user-material subroutine-VUMAT consisting of Hashin and Puck failure criteria and the damage evolution model based on the equivalent-strain method to predict the initiation and evolution of damage for matrix and fiber. In the research process, the impact resistance performance of auxetic laminates is evaluated in comparison with composite laminates with positive Poisson's ratio with cross-ply and angle-ply sequences. The results showed that in some damage modes, auxetic behavior can lead to the improvement of composite laminate damage. Based on the analysis of the results, the highest damage amount of delamination, matrix tension, matrix compression, and fiber tension damage is observed in angle-ply, through-thickness auxetic, cross-ply, and through-thickness auxetic laminates, respectively. Meanwhile, cross-ply, angle-ply, and through-thickness auxetic laminates with characteristics such as high impact force, low impact time, low maximum displacement, and less dissipated energy than in-plane auxetic laminate are suitable for use in structures with hardwall design approach. Also, the in-plane auxetic laminate with features such as low impact force, high impact time, high displacement, and more dissipated energy than other composite laminates, is practical and operational for use in sacrificial structures.

This study conducts a parametric analysis as well as performance evaluation of a multiuple effect distillation system equipped with a thermocompressor. Equations for mass, salt concentration, energy, and exergy for each component of the desalination system are established. The study proceeds with an investigation and analysis of this system using the EES (Engineering Equation Solver) software. This research examines the effects of Top Brine Temperature (TBT), water concentration, and the number of effects on the flow rate of the cooling water in the condenser, the flow rate of produced fresh water, the performance ratio, specific area, the rate of exergy destruction, and the efficiency of exergy. The findings show that the eight-stage desalination system achieves the highest performance ratio under specific system input conditions. Additionally, the exergy analysis reveals that the exergy destruction rates for the evaporators (effects), the condenser, the thermocompressor, and the pumps are 5146, 3266, 1568 and 366 kW respectively, with the highest to the lowest exergy destruction correspondingly attributed to the evaporators and the pumps.

The abstract should be written with 100 to 200 words (Times New Roman 9). The most complete method to calculate aerothermodynamics and radiation heating applied to the walls of the hypersonic destructible is simultaneous solution of flow equations, chemical reaction kinetics, combustion model in the destructible layer, radiation models and flow turbulence. Using this algorithm over time requires a high amount of computing memory. Due to the high solution time, the users of this code do not consider it reasonable to use it for preliminary design purposes. Therefore, the aim of this research is to compile the dimensionless number RN by using the results of CTCA code and Buckingham's method to determine the boundary between aerothermodynamics and radiation heating in order to reduce the solution time related to CTCA code, so that in RN smaller than 1.0, it is possible to calculate the heating ignore radiation versus aerothermodynamics heating and disable the subroutine related to radiation heating, and also in RN greater than 2.0, you can ignore aerothermodynamics heating versus radiation heating and disable the subroutine related to aerothermodynamics heating. By considering these changes on CTCA code, its solution time for a nose with a typical flight envelope was reduced by 15%, the maximum amount of error in the total heat flux compared to CTCA code was less than 2%. It should be noted that in the1≤RN≤2, the effects of aerothermodynamics and radiation heating should be considered simultaneously and the relevant subroutines in CTCA code should be activated.

Providing electrical, thermal and cooling energy in greenhouses is a very important issue. Due to the low efficiency of most of the conventional systems in greenhouses, the use of simultaneous production of electricity, heat and cooling (CCHP) systems has been highly considered in recent years. The main purpose of this article is the technical and economic feasibility of CCHP technology for use in a greenhouse in Tehran. In this research, a cucumber greenhouse with an area of 1 hectare, which consists of two structures of 0.5 hectare, has been analyzed and investigated. In order to analyze the technical-economic system used, calculations for four scenarios including the basic and conventional system, CCHP with absorption chiller and selling electricity to the grid, CCHP with absorption chiller and self-supply and CCHP with compression chiller and self-supply accepted. According to the results obtained for each scenario as well as the comparison of the selected scenarios, the greenhouse considered for the implementation of the CCHP system is not economical. The results of the research show that in case of using the CCHP system with absorption chiller and selling electricity to the grid, in order to make the system economical, the minimum rate of buying electricity from these units should be 3223 Rials per kilowatt hour. In the CCHP system with absorption chiller and self-supply, if the location of the greenhouse is such that 176 kilometers of transmission line is needed, this scenario becomes economical.

Studies show that the analysis of the first law in air propulsion systems alone is not sufficient, and for a complete study of a system, the second law and exergy analysis should also be considered. Thermodynamic analysis of air-breathing engines, especially Turbojet, Turbofan and Turboprop engines, with the aim of studying their performance has attracted the attention of many researchers in the last decade. The main purpose of this study is to review and present the latest research findings in this field focusing on Turbojet, Turbofan and Turboprop engines. The results of further research show that the combustion chamber and afterburner are the two most important parts of air engines in which the most exergy destruction occurs. On the other hand, the study and analysis of engine exergy off design point is also an important issue that has been considered in recent years.

In this paper, the flow field is investigated by solving the fluid dynamics and acoustics of the launch vehicle for a specific sample model with Fluent software. The model used in this research has been studied acoustically in one of the essays previously in the laboratory. The components that constitute the launch vehicle affect the level of noise exerted to the rocket as it rises. In the present study, an attempt is made to numerically examine the contribution of a component of the main launch structure, namely the launch pad, to the acoustics and the flow field around the known launch vehicle whose experimental information is available on a jet output current deflector. For this purpose, in order to ensure the numerical solution, the flow field of the fluid exiting the projectile jet was investigated in terms of pressure and flow velocity parameters as well as Mach number, which was in accordance with the experimental conditions presented in the experimental work. Then the acoustic power values were obtained as a contour on the current field symmetry plane by software. The size of the acoustic pressure level at the location of the sensors identified in the experimental work was determined in the present study and calculated according to the results of acoustic information. Comparison of acoustic results from numerical solution at near field sensors showed very close agreement in less than 3.3%. the difference is close to 8.9%, which is more than the near field results.