نشریه مهندسی مکانیک و ارتعاشات
سال ششم شماره 4 (پیاپی 21، زمستان 1394)

To ensure the safety of structures and their serviceability for the sightly purposes, all structures, especially important structures, needs continuous and regular evaluation and monitoring. For this reason, methods for monitoring and damages detection in structures, has emerged. In this article, using wavelet transform method, damages detection in plates with different supporting conditions, is discussed. For this reason, a squre plate with one meter side is considered and supposes its support conditions as four fixed sides, four bearing sides, three fixed sides and cantilever. Damages modeled by rectangular cracks with thickness reduction method. For each supporting state, cracks with different depth checked. Finally, obtained responses from plate finite element analysis, using two-dimensional discrete wavelet transform, analyze and detectable most shallow crack, at any supporting state, is obtained. It can be seen that, this method shows the crack locations by peak points and abrupt changes in wavelet coefficient graph, and that in four fixed sides state, cracks down to one percent relative depth, in three fixed sides state, cracks down to three percent relative depth, in four bearing sides state, cracks down to six percent relative depth and in cantilever state, cracks down to 30 percent relative depth, are detectable. It can be seen that, by increasing the plate fixity, ability of the proposed method to detect tiny cracks will further. The obtained results are useful for design and evaluation of plate form structures and prevent the formation and progression of tiny cracks.

In this paper, dynamic response of an infinite Timoshenko beam subjected to a harmonic moving load based on the first order shear deformation theory (FSDT) is studied. The beam made of a symmetric laminated composite that is located on a generalized Pasternak viscoelastic foundation. It is assumed that the mechanical properties of the beam change in the direction of the beam thickness but remain constant in the axial direction. By selection of an appropriate displacement field for the composite beam, and using the principle of total minimum potential energy, the governing partial differential equations of motion are obtained and solved through a complex infinite Fourier transformation method. In this study, by using numerical simulation, the effects of stiffness, damping and shear layer viscosity coefficient of foundation, velocity and frequency of the moving load over the beam response are studied. Then, the numerical simulation results for deflection, shear force and bending stress are abtained. The results show that, when the normal stiffness, shear layer viscosity coefficient, velocity and frequency of the moving load increases, the deflection, shear force and bending stress of the composite beam decreases. The results obtained from the FSDT are compared with the results of a finite element and good agreement is found. Therefore, the dynamic responses of the composite beam under moving load can be found with high accuracy by using the finite element method.

The most important part of the Stirling engine that has an important role in improving efficiency, heat recovery. Stirling cycle heat recovery is one of the important parts of that model because of the influence of various parameters is very complex. In terms of physical structure, heat recovery from stainless steel sheet, stainless steel net or stacked bars, are made. Over half of the engine cycle, heat recovery heat like a sponge to absorb the heat of the operating gas. In the other half cycle, recovery of heat after the gas, so less heat to ward off the cold the engine, there will be a way to increase engine efficiency. Therefore, the recovery Stirling engine reduces heat loss and thus increasing the engine's efficiency. The development of an appropriate thermodynamic model for beta type Stirling engine, has been the recovery area. This model, predict and optimize power output and performance parameters based on the physical conditions and geometric Stirling engine regenerator requirements. For this purpose, the numerical solution of beta type Stirling engine uses isothermal and adiabatic model is done. To validate the results, the geometric and functional Stirling engine manufactured by General Motors used and the results were compared with published values.

Modern man is facing two major problems; On the one hand, fossil fuels are running out and the other side, these fuels environmental problems such as air pollution and the greenhouse effect, making them much. Solar cell is the best choice to replace fossil fuels. In this study, using the software scaps Initial simulation for solar cells has been considered. The investigation revealed that for best performance, Should be as thin with a thickness of 4 µm tin And zinc oxide used as window that if we can keep constant temperature of the solar cell at 300 K have the highest efficiency.

The various methods for energy conservation and energy efficiency in industry, and renewable energy as one of the main factors for the formation and development of industrial societies known. Due to the reduction of fossil fuels, their growing need for communities to energy price increases, the phenomenon of thermoelectric waste heat recovery and recycling in various parts of the human body can be used. Different parts of the body have different temperature, an average temperature of the body is mainly about 37.5 ° C is accepted, but an average temperature of about 32° C is the skin. Since the temperature of the skin over the ambient temperature is the temperature difference, the thermal energy contained in the skin can be used to generate electric power using heat recovery can be used. Electric power generation in the absence of the temperature difference between the body and the environment is poor, but through optimization heat sink recycling device can be improved output voltage The advantages of thermoelectric technology can be clean and quiet, the lack of mechanical parts, simple maintenance, low weight and long life that is nearly 100 thousand hours mentioned. The aim of this study was to investigate the feasibility of thermoelectric modules to produce power from heat output is human skin. The results of the modeling show that the temperature difference across the thermoelectric more electrical power will increase.

The aim of the present study is to investigate the applications of nanofluids in various industrial and engineering applications. Nanofluids are new types of fluids produced by dispersing Nano-particles in a base fluid. Nowadays, regarding the fact that the applications of nanofluids in thermal systems, motor oils, lubricants and so forth are flourishing and booming day by day, these fluids have been strongly in the spotlight of researchers. In this study, the applications of nanofluids in heat exchangers, chillers, machining, solar water heating, engine cooling, cooling of electronic components, oscillating heat pipe, and cooling nuclear reactors have been investigated. The results showed that nanofluids possess grater thermal conductivity compared with those of conventional fluids.

Testing activities takes 50% of overall cost of software development process. In order to perform software testing, a set of test cases should be generated. Generating this set is so time consuming and have a direct impact on the cost of software testing. Without automation, this process is slow, expensive and error prone. In this paper, a new approach in order to generate test cases based on random testing by combining static and dynamic information is proposed. The proposed approach generates test cases by utilizing the simple nature of random testing and also using the information which can be gained by the source code that leads to improve in the performance of random testing. The experimental results indicate an increase in the test case generation speed and also quality of test suite.