مجله مهندسی مکانیک
سال چهل و ششم شماره 1 (پیاپی 74، بهار 1395)

In this paper, the free vibration of a two dimensional functionally graded (2D-FG) cylindrical shell is studied. The mechanical properties of the material alter continuously through its both length and thickness of cylindrical shell based on the power law distribution of volume fraction. The governing equations of motion are achieved by using Hamilton’s principal based on the first order shear deformation theory. Since there is no closed form solution, the generalized differential quadrature (GDQ) method is applied for solving equations with assuming simply supported for both end of cylindrical shell. To verify the results, they are compared with the finite element analysis and the results of other literatures. It is shown there is a good agreement between the results. Finally, the effects of shell geometry parameters and the volume fraction exponent on the natural frequencies and the mode shapes of 2D-FG cylindrical shell are investigated. The results show that the natural frequencies of the 2D-FG cylindrical shells are higher than the conventional FG cylindrical shells at the same geometric conditions. In fact, the natural frequency of 2D-FG cylindrical shell can be controlled using more parameters and proper selection of basic material.

The present paper developsa numerical procedure(finite difference) for the calculation of turbulent combustive flows and simulation of production of NOXpollutants in converging and diverging ducts. Also this paper reports the results of a numerical investigation of the effects of the equivalence ratio and diverging angle on NOXemissions. Our results indicate the important influence of the limiting diverging angle of diffuser on the coefficient of pressure recovery. Moreover, due to its intense dependence on the maximum temperature in the domain, the NOXpollutant amount attained also maximum level. By increasing the equivalence ratio, maximum temperature and also NOXpollutant increase.

This article studies the solid propellant rocket motor internal ballistic simulation with multi segmented grain and system engineering approach. Once grain is segmented, the alternative cross-burning Surfaces are added to combustion process. This simulation can estimate all motor performance parameters and satisfy thrust considered by mission. Synthesis and integration of all equations, modeling and relations correction in accordance with the proposed method, feasibility and effectiveness of method along with design, manufacture and test of one engineering prototype motor are the main goals of this study. Motor components are; Combustion chamber, grain, burning surface and nozzle. In this study, two main approaches are included; first is preparing a numerical program in accordance with the proposed method and second is technical requirements of production, static testing with data recording and analyzing. Determining all the inputs and outputs, effective interrelated data communication, correct and improve the calculation accuracy, simplicity and high speed calculation are advantages of the program. Finally, a complete prototype motor was manufactured and productive force was measured using a standard static test stand. Thrust force comparison between numerical and test output are show results matching.

In this paper 3D mixed-mode crack analysis of gas turbine blade is performedby using the finite element method and the path independent J integral.The effect of different parameters like rotation speed ofthe blade, fluid pressure, crack angle, crack position on the blade and crack length on the stress intensity factors of mode I, II, III and effective are investigated.Moreover critical rotational speed and critical crack length, height and angle are estimated too.Results are alsoshow, the edge cracks might grow form surface crack tip, so Surveillance of crack outer surface assurance the safety in the blade.

The paper concerns with the transient response analysis of the nondestructive infrared thermography test to detect thedelaminationsin the laminated composites. A thermal pulse flow is applied to the surface of composite samples and the dimension and position of delamination defects are determined based on the temperature distribution analysis of the heating surface. The transient thermal response is determined by finite element model of laminated composite subjected to heat flux of halogen lamp in a short time period and natural cooling convection flow on the specimen surfaces at long time. The thermography model is implemented for a laminated composite sheet with different size delaminations located at multiple depths. Thin aluminum layers are considered on the composite surfaces to uniform heat transfer. The numerical results show that temperature gradient is observed at specific time range on heating surface due to considerable thermal resistance variation of defects and the temperature distribution can be used to detect the small size delaminating in the laminated composites The temperature distribution and spatial derivation result in the exact size of damage regions and the optimum inspection time leading to appropriate results in impulsive infrared thermography test.

In this study, fluid flow and thermal mixing in a rotating curved rectangular micro-channel have been investigated numerically. The continuity, momentum and energy equations have been solved by finite difference projection method using a program written in FORTRAN programming language. No-slip and adiabatic boundary conditions have been applied for channel walls and the numerical results have been validated by comparison of friction factor with previous results for stationary micro-channels in literature. The effect of flow parameters such as De and Ro numbers on the flow pattern has been studied and shows that these parameters can change the friction factor and mixing index by altering the flow pattern. Furthermore, the effect of aspect ratio of micro-channel cross section on the flow pattern, friction factor and mixing index has been studied and shows that the aspect ratio can affect the friction factor and mixing index. The results show that, there are distinguished optimal aspect ratios for low and high De numbers. Studying the variation of mixing index in the channel demonstrated the improvement of mixing index by increasing the channel length.

Point-based models have been analyzed for different applications and depending on the demand, features are extracted by various algorithms. Surfacerecognition from point clouds is most applicable problem in machine vision and reverse engineering. In this research for estimating design parameters, planes and cylinders in point clouds are investigated and new algorithm for detecting these surfaces and calculate their parameters is proposed. According to proposed method, at first surface normal vector by using nearest neighbors must be estimated. By using surface normal vector homogeneous neighborhood is selected. Umbrella curvature is then calculated using homogeneous neighbors. The points are grouping by umbrella curvature as a criterion. Planes and Cylinders are detected by analyzing umbrella curvature values and pattern of homogeneous neighbors. A new method for calculation of planes and cylinders parameters is proposed. This method used fordetermining parameters of eachgroup of points. For evaluation that the proposed algorithm, the calculated parameters are compared with parameters are measured by coordinate measuring machine (CMM). Analyzing results shows that the proposed algorithm performs well and has appropriate abilities on automatic detection of cylinders and planes and calculation their parameters.

CO2 is the main greenhouse gas due to the very high overall amount emitted by human activities, and about one third of the overall human CO2 emissions are produced by the power generation sector. Oxy-fuel cycles are a promising technology. From the other side because of the fuel consumption in the power generation sections, thermodynamic analysis has an important role. In this study we are going to analyze the cycle and all the units thermodynamically and propose some information about the energy and exergy efficiency of them. Energy and exergy efficiency are 53.25% and 46.45% respectively and as it was predictable the main part of exergy destruction occurs in the combustion chamber. Solving simultaneous equations has been done by the EES software.

Experimental study of convective heat transfer in nano-fluid, containing Fe3O4powder nano-particles without stabilizer and nano-fluid containing colloidal nanoparticles of Fe3O4, with stabilizer, is the main aim of this work. For this purpose, the Nytro Libra oil, as a conventional oil in power transformers has been considered as the base oil. Results show thatthe use of nanoparticles, improves the base fluid heat transfer characteristics. Alsobased on the experimental observations, the use of nanoparticles in the powder form, decreases and in the colloidal form increases the dielectric properties of transformer oil. Hence, the thermal behavior of the two types of nano-oils would be important. The results in present study showed that the convective heat transfer coefficient of nanofluid, containing nano-particles in the powder form in a tube with constant heat flux, and volume concentration of 0.1% and 0.3%, is 7% and 9.5% mare than nano-oil containing colloidal particles and also 6.5% and 2.4% higher than the base oil, respectively. Finally, thermal behavior of different nano-oils samples are discussed, and other researcher’s arguments are also taken into consideration.

Operational assessment of Electronic Wave Measurement sensors and calibration of accelerometer, gyro sensors were considered. The designation and implementation of accelerometer, gyro and compass was done due to Micro Electro Mechanical systems (MEMS) technology and with regards to diversity method to promote the performance. The investigations were done by ... and ... due to experimental aspects. Besides, operational assessment of Electronic Wave Measurement sensors was invoked by analytic results in time and frequency domain and by field results generated from a referenced Wave Measurement Sensor.

This paper identifies the inefficiencies of a proposed energy conversion system to improve its performance. The conventional exergy analysis is unable to identify these inefficiencies because it does not consider the interactions among the system components. The advanced exergy analysis does this however. The main role of advanced exergy analysis is to provide engineers with additional useful information for improving the design and operation of energy conversion systems. The information is achieved by splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts. In the present paper both the conventional and advanced exergy analyses are employed. The splitting raises the accuracy of exergy analysis and facilitates the system improvement. The used method in this paper for splitting is thermodynamic cyclemethod which considers hybrid cycles in each of which only one of the component operates on the real condition and the rest operate under ideal condition. Advanced exergy analysis of ejector-expansion trans-critical CO2 cascade refrigeration system consisting of two refrigeration systems, is discussed. The results indicate that although the conventional exergy analysis shows the highest exergy destruction for the ejector, the advanced exergy analysis suggests improving the gas cooler performance first. The compressor, ejector and evaporator are in the next stages for improvement because of their maximum value of endogenous avoidable exergy destructions.