مجله مهندسی مکانیک
سال چهل و پنجم شماره 1 (پیاپی 70، بهار 1394)

Wind tunnels generate controlled air flow which passes through the model. Thus، a series of useful data related to air flow quality are obtained. The final goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. One of the methods for decreasing the turbulence intensity is to install honeycomb and screens in the settling chamber of the wind tunnel. In this research، the effects of honeycomb and screens with specified geometric parameters on velocity distribution، turbulence intensity، skewness and flatness are investigated. A set of hot-wire anemometer is used to measure turbulence intensities. It measures flow instantaneous velocity with high frequency. The results show that the installation of honeycomb and screens، and isolation of the test section from the fan decreases the turbulence intensity of the test section about 75% and، optimizes the skewness and flatness values. Moreover، normal probability distribution of instantaneous velocity approaches the normal distribution.

In the present research، the effects of the shape and size nugget variations in the AISI 1008 resistance spot weldment were showed by the parametric study using the finite element method. The verification of some of the finite element results was done by comparison with the experimental study results and other was compared with the published researchs. The results show that the electrical current is the most important parameter in the formation of the nugget. The heat affected zone was grown by increasing the electrode diameter and the sheet thickness; as a result the time and the electrical current should be increased for welding. In addition، the nugget size was reduced and the temperature gradiant in the heat affected zone was raised by decreasing the electrical current and the welding time، as a result the tension residual stresses in the heat affected zone were increased.

In this study، the method of measuring the viscoelastic and hyper-elastic property of rubbers is explained. After that a sandwich cantilever with core of rubber is simulated and the simulated results are compared with experimental results. The main parameters like loss factor and storage module for simulating rubber behavior are explained. Next، the ways for measuring of these parameters is described. Finally، this property is used for ABAQUS and results is compared with experimental test.

In this research، a thixoforging process is studied as one of the semi-solid forming processes that include aluminum alloy forging in two-phase temperature range (between solidus and liquidus). For this purpose and in order to achieve favorable conditions in the two-phase zone، the influence of reheating temperature and holding time on thixoforging process is investigated. Semi-solid temperature and holding time are considered 580، 590، 600 °C and 5، 10، 15 minutes respectively. Attained results show that the finest microstructure (73 micrometer) is obtained in semi-solid temperature of 600°C and holding time of 5 minutes. Also، the hardness and the compressive test are performed in order to find the best mechanical properties. As it is expected، the best mechanical properties (yield stress of 149 MPa، ultimate compressive stress of 433 MPa and hardness of 79 VHN) are achieved in sample with the finest structure.

In this research، a thixoforging process is studied as one of the semi-solid forming processes that include aluminum alloy forging in two-phase temperature range (between solidus and liquidus). For this purpose and in order to achieve favorable conditions in the two-phase zone، the influence of reheating temperature and holding time on thixoforging process is investigated. Semi-solid temperature and holding time are considered 580، 590، 600 °C and 5، 10، 15 minutes respectively. Attained results show that the finest microstructure (73 micrometer) is obtained in semi-solid temperature of 600°C and holding time of 5 minutes. Also، the hardness and the compressive test are performed in order to find the best mechanical properties. As it is expected، the best mechanical properties (yield stress of 149 MPa، ultimate compressive stress of 433 MPa and hardness of 79 VHN) are achieved in sample with the finest structure.

The present study investigates the flow through the actual stenosed artery due to the Atherosclerosis، both numerically and experimentally. The governing differential equations of blood flow are solved by controlvolume techniques in the generalized body-fitted coordinates because of the complex geometry. The aim of this study is isolate the effect of actual stenosed geometry on the flow characteristics such as، velocity and pressure profiles، velocity vectors and mean and local wall shear stress in the post-stenotic. It is shown that the oscillation and sudden increase of wall shear stress is found to relate to the increasing Reynolds number at the neck of stenosis، which is an important factor in progress of arterial disease.

This paper the presents modeling and monitoring of Shiraz solar power plant oil cycle. The different parts of the process which influence the control performance are modeled and validated with the real data from Shiraz solar power plant in MATLAB software environment. The developed model structure is based on the process flow diagram (PFD) of Shiraz solar power plant was performed. To create an environment with better user interface and more flexibility for real-time connections، the developed model is transferred to Labview software environment. It provides proper GUI software to monitor different performance trends of the plant.

In this paper، optimization of heat exchangers of a geothermal power plant، based on genetic algorithm، has been studied. At first، the optimized inner to outer diameter ratio is calculated based on one-objective optimization function، for the pressure drop per unit length as well as the power plant thermal efficiency. Then، the multi-objective optimization is performed based on the geothermal power plant thermal efficiency and the cost of the geothermal components cost as two-objective functions. In this study، the cost of geothermal well piping installation and well depth estimation are considered. One-objective optimization results lead to optimized inner to outer diameter ratio of 0. 675 and 0. 353 for the least pressure drop and the maximum thermal efficiency respectively. The two-objective optimization parameters were identified in order to increase efficiency and reduce costs.