نشریه مهندسی مکانیک و ارتعاشات
سال نهم شماره 4 (پیاپی 33، زمستان 1397)

In this thesis, using the Euler-Bernoulli beam model and Eringen nonlocal elasticity theory, also taking into account the effects of Coriolis acceleration, the equations of the vibration of the rotating nanotubes are governed. Moreover the forces imposing on the rotating nanotubes under the influence of vibrations from the internal flow side using the theory of slender body theorem is simulated and calculated. By combining the governing equations on the axial axis of nanotube, the equations of internal forces from the internal flow of the system are extracted. Then, using eigenvalue analysis methods, the natural frequencies of the vibration is governed and its stability at Different rotation speeds and axiality are studied. Also, the effects of parameters such as rotational speed, axial flow velocity, mass ratio of internal flow to mass axis, slip coefficient, and ... on the study boundary of stability will be investigated

The main aim of this study is the investigation of the mechanical vibration parameters using Taguchi method in the semi-solid casting of AL-A380. This research has been done to improve the mechanical properties and the development of this alloy for the construction of the powertrains vehicle’s Shell pinion and gearbox. Grain diameter, hardness and porosity of samples were examined as important features of this research outputs. The results showed that the vibration of melt with suitable intensity and enough the period of time caused to decrease of the particle diameter and increase of the hardness. But with increasing of vibration intensity the porosity was increased especially at the high temperatures of vibration. In this research, the primary hardness that was measured around 80 BHN had increased to 100 BHN in condition of 595°C the melt temperature, vibration intensity of 90 Hz at the 30 seconds of the period of time. It was also observed in microstructure study that using this method, the microstructure was broken from the dendritic form to the spherical ones with the grain diameter of 32 micrometers.

Porous materials are encountered literally everywhere in everyday life, in technology, and in nature. With the exception of metals, some dense rocks, and some plastics, virtually all solid and semisolid materials are "porous" to varying degrees. There are many examples of porous materials in everyday life and the environment. Textiles and leathers are highly porous; they owe their thermal insulating properties, as well as the property that they "breath ," to their pore structure. Paper towels and tissue paper are also highly porous; these owe their absorbency partly to their porous structure and partly to the property that they are strongly wetted by water. In this study, mathematical model and formula based on porous media will be discuses.

In the present study, the effects of defects in the honeycomb structure on the capability of the energy absorption are investigated using the finite element method in ABAQUS software. By simulation using quasi-static analysis, the effects of the geometric dimensions of the defect and different geometries of honeycomb cells on the energy absorption of the structure have been investigated. In the analysis, for each case three percent of defects, including 0, 10 and 30% were studied. The results show that the honeycomb structure with A-type cell geometry is completely destroyed, which can be due to the asymmetry of the structural cells. In the other two models, the structure retains its overall shape and by systematic modification of the cells, they have the ability to absorb energy during the collision. Also, the results show that the defects in these structures have a significant effect on their energy absorption capacity in which by increasing the defects, the energy absorption capacity decreases.

This paper deals with transverse crack identification in rotating shafts. In this research, after presenting the equations governing the problem, different depths and positions of crack in a rotating axis of an industrial compressor unit is investigated using a breathing crack model. Crack is modeled based on the principles of fracture mechanics and the system's motion equations are extracted. Stress intensity coefficients are implemented to model the actual crack behavior in gradual opening and closeing situations. The results showed that in the points where the cracks are closed, the stiffness has its maximum value. Also, with increasing crack depth, the total stiffness of the shaft decreases. The first harmonic in the frequency corresponds to imnbalance and the second harmonic associated with the crack effect. By changing the position of the crack from the ends to the center of the shaft, the frequency of the second harmonic decreases while its amplitude decreases. Inverse analysis can be carried out based on the second frequency along with its amplitude in order to crack identification.

Energy consumption is high for building comfort; since windows in warm seasons can bring a lot of radiant energy into the building, which leads to an increase in cooling energy, creating a shadow on this window to prevent sunlight from entering the building along The year is important. In this article, we have been using horizontal awnings for the windows of the Amphitheater Building of Semnan Azad University and we have been using the design of the Designer Bilder and we have investigated the effect of the canopy on the thermal load of the building and the magnitude of the brightness of the amphitheater building of the Semnan Azad University. Shows a horizontal awning with a 50cm

Due to the importance of water hammer in pipe network and pipe containing liquids in this paper, the diameter of pipe and the velocity of fluid were considered experimentally in laboratory and simulated the problem in HAMMER software. In this study, the tests were carried out with six different types of materials (Brass, Carbon Steel, Copper, Five layer and PVC). It was assumed that valve which causes water hammer was closed fast. Also, how valve closing, is another important issue for this phenomenon. The tests in two modes slow and fast closing valve results showed if it takes more time to close, water hammer is less and the waves would fade faster. Also by examining the results indicate that the diameter of the pipes increasing pipe's diameter, increases the mess flow and fluid's velocity therefore effect of water hammer increases. This phenomenon shows that effect of increasing fluid velocity is more powerful than increasing pipe diameter.